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[J 1] Energy Efficiency and Spectral Efficiency Tradeoff in RIS-Aided Multiuser MIMO Uplink Transmission

L. You, J. Xiong, Derrick Wing Kwan Ng, C. Yuen, W. Wang, and X. Gao,
Journal Paper accepted for publication, IEEE Trans. Signal Process., Dec. 2020.

[J 2] Location-aware Predictive Beamforming for UAV Communications: A Deep Learning Approach

C. Liu, W. Yuan, Z. Wei, X. Liu, and Derrick Wing Kwan Ng,
Journal Paper accepted for publication, IEEE Wireless Commun. Letters, Dec. 2020

[J 3] Sum-Rate Maximization for IRS-Assisted UAV OFDMA Communication Systems

Z. Wei, Y. Cai, Z. Sun, Derrick Wing Kwan Ng, J. Yuan, M. Zhou, and L. Sun,
Journal Paper accepted for publication, IEEE IEEE Trans. Commun., Dec., 2020.

[J 4] Intelligent Reflecting Surface-Aided Joint Processing Coordinated Multipoint Transmission

M. Hua, Q. Wu, Derrick Wing Kwan Ng, J. Zhao, and L. Yang,
Journal Paper accepted for publication, IEEE IEEE Trans. Commun., Nov., 2020.

[J 5] Cooperative Activity Detection: Sourced and Unsourced Massive Random Access Paradigms

X. Shao, X. Chen, Derrick Wing Kwan Ng, C. Zhong, and Z. Zhang
Journal Paper accepted for publication, IEEE Trans. Signal Process., Nov., 2020.

[J 6] Deep Transfer Learning for Signal Detection in Ambient Backscatter Communications

C. Liu, Z. Wei, Derrick Wing Kwan Ng, J. Yuan, and Y.-C. Liang,
Journal Paper accepted for publication, IEEE Trans. Commun., Oct. 2020

[J 7] Bayesian Predictive Beamforming for Vehicular Networks: A Low-overhead Joint Radar-Communication Approach

W. Yuan, F. Liu, C. Masouros, J. Yuan, Derrick Wing Kwan Ng, and N. González-Prelcic
Journal Paper accepted for publication, IEEE Trans. Commun., Oct. 2020

[J 8] Resource Allocation for MIMO Full-Duplex Backscatter Assisted Wireless-Powered Communication Network with Finite Alphabet Inputs

F. Ke, Y. Peng, Y. Peng, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Trans. Commun., Oct. 2020

[J 9] Beamforming Optimization for IRS-Aided Communications with Transceiver Hardware Impairments

H. Shen, W. Xu, S. Gong, C. Zhao, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Trans. Commun., Oct. 2020.

[J 10] Joint Radio Resource Allocation and Cooperative Caching in PD-NOMA-Based HetNets

M. Moghimi, A. Zakeri, M. R. Javan, N. Mokari, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Trans. Mobile Computing, Oct. 2020.

[J 11] Deep Residual Learning- Assisted Channel Estimation in Ambient Backscatter Communications

X. Liu, C. Liu, Y. Li, B. Vucetic, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Wireless Commun. Letters, Oct. 2020.

[J 12] Cascaded Channel Estimation for IRS-assisted Mmwave Multi-antenna with Quantized Beamforming

W. Zhang, J. Xu, W. Xu, Derrick Wing Kwan Ng, and H. Sun
Journal Paper Accepted for publication, IEEE Trans. Wireless Commun., Sep. 2020

[J 13] Distritbuted IRS with Statistical Passive Beamforming for MISO Communications

Y. Gao, J. Xu, W. Xu, Derrick Wing Kwan Ng, and M.-S. Alouini
Journal Paper Accepted for publication, IEEE Trans. Wireless Commun., Sep. 2020

[J 14] Cycle-Slip Detection and Correction for Carrier Phase Synchronization in Coded Systems

D. Shi, W.Yuan, S. Li, N. Wu, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Commun. Letters, Sep. 2020.

[J 15] Robust secure beamforming design for two-user downlink MISO rate-splitting systems

D. Xu, X. Yu, Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Journal Paper Accepted for publication, IEEE Trans. Wireless Commun., Aug. 2020.

[J 16] Resource Allocation for IRS-assisted Full-Duplex Cognitive Radio Systems

D. Xu, X. Yu, Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Journal Paper Accepted for publication, IEEE Trans. Commun., Aug. 2020.

[J 17] Beamforming design for secure MISO visible light communication networks with SLIPT

X. Liu, Y. Wang, F. Zhou, S. Ma, R. Q. Hu, and Derrick Wing Kwan Ng,
Journal Paper Accepted for publication, IEEE Trans. Commun., Aug. 2020.

[J 18] Massive access for 5G and beyond

X. Chen, Derrick Wing Kwan Ng, W. Yu, E. G. Larsson, N. Al-Dhahir, and R. Schober
Journal Paper Accepted for publication, IEEE JSAC, Jul. 2020

[J 19] Learning-based Predictive Beamforming for UAV Communications with Jittering

W. Yuan, C. Liu, F. Liu, S. Li, andDerrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Wireless Commun. Letters

[J 20] On the Performance of LTE/Wi-Fi Dual-Mode Uplink Transmission: Connection Probability versus Energy Efficiency

J. Zhang, J. Han, L. Xiang, Derrick Wing Kwan Ng, M. Chen, and M. Jo
Journal Paper Accepted for publication, IEEE Trans. on Veh. Technol., Jul. 2020.

[J 21] Max-Min Energy Balance in Wireless-Powered Hierarchical Fog-Cloud Computing Networks

J. Liu, K. Xiong, Derrick Wing Kwan Ng, P. Fan, Z. Zhong, and K. B. Letaief
Journal Paper Accepted for publication, IEEE Trans. Wireless Commun., Jul. 2020.

[J 22] Energy Efficiency in Secure IRS-Aided SWIPT

J. Liu, K. Xiong, Y. Lu, Derrick Wing Kwan Ng, Z. Zhong, and Z. Han,
Journal Paper Accepted for publication, IEEE Wireless Commun. Letters, Jun. 2020.

[J 23] Joint Channel Estimation and Equalization for Index-Modulated Spectrally Efficient Frequency Division Multiplexing Systems

Y. Ma, N. Wu, W. Yuan, Derrick Wing Kwan Ng, and L. Hanzo
Journal Paper Accepted for publication, IEEE Trans. Commun., Jun. 2020

[J 24] Tradeoff Between Ergodic Energy Efficiency and Spectral Efficiency in D2D Communications Under Rician Fading Channel

M. R. Mili, Ata Khalili, N. Mokari, S. Wittevrongel, Derrick Wing Kwan Ng, and H. Steendam
Journal Paper Accepted for publication, IEEE Trans. on Veh. Technol., Jun. 2020

[J 25] Jamming-Resilient Frequency Hopping-Aided Secure Communication for Internet-of-Things in the Presence of an Untrusted Relay

M. Letafati, A. Kuhestani, H. Behroozi, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Trans. Wireless Commun., Jun. 2020.

[J 26] Time-Domain vs. Frequency-Domain Equalization for FTN Signaling

S. Li, W. Yuan, J. Yuan, B. Bai, Derrick Wing Kwan Ng, and L. Hanzo
Journal Paper Accepted for publication, IEEE Trans. on Veh. Technol., Jun. 2020.

[J 27] Secrecy Performance for Finite-Alphabet Inputs Over Fluctuating Two-Ray Channels

C. Ouyang, S. Wu, C. Jiang, Derrick Wing Kwan Ng, and H.Yang,
Journal Paper Accepted for publication, IEEE Wireless Commun. Letters, Jan. 2020.

[J 28] Design, Analysis and Optimization of a Large Intelligent Reflecting Surface Aided B5G Cellular Internet of Things

G.Yu, X. Chen, C.Zhong, Derrick Wing Kwan Ng, and Z. Zhang,
Journal Paper Accepted for publication, IEEE Trans. IoT, May 2020.

[J 29] Robust and Secure Wireless Communications via Intelligent Reflecting Surfaces

X. Yu, D. Xu, Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Journal Paper Accepted for publication, IEEE JSAC, May 2020.

Abstract: In this paper, intelligent reflecting surfaces (IRSs)are employed to enhance the physical layer security in a challenging radio environment. In particular, a multi-antenna access point(AP) has to serve multiple single-antenna legitimate users, which do not have line-of-sight communication links, in the presence of multiple multi-antenna potential eavesdroppers whose channel state information (CSI) is not perfectly known. Artificial noise(AN) is transmitted from the AP to deliberately impair the eavesdropping channels for security provisioning. We investigate the joint design of the beamformers and AN covariance matrix at the AP and the phase shifters at the IRSs for maximization of the system sum-rate while limiting the maximum informationleakage to the potential eavesdroppers. To this end, we formulate a robust non-convex optimization problem taking into account the impact of the imperfect CSI of the eavesdropping channels.To address the non-convexity of the optimization problem, an efficient algorithm is developed by capitalizing on alternating optimization, a penalty-based approach, successive convex approximation, and semidefinite relaxation. Simulation results show that IRSs can significantly improve the system secrecyperformance compared to conventional architectures withoutIRS. Furthermore, our results unveil that, for physical layersecurity, uniformly distributing the reflecting elements among multiple IRSs is preferable over deploying them at a single IRS

[J 30] A Simple Variational Bayes Detector for Orthogonal Time Frequency Space (OTFS) Modulation

W. Yuan, Z. Wei, J. Yuan, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Trans. Veh. Technol., Apr. 2020

Abstract:

[J 31] Distributed Estimation Framework for Beyond 5G Intelligent Vehicular Networks

W. Yuan, S. Li, and and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Open Journal of Vehicular Technology, Apr. 2020.

Abstract:

[J 32] Energy-Constrained UAV-Assisted Secure Communications with Position Optimization and Cooperative Jamming

W. Wang, X. Li, M. Zhang, K. Cumanan, Derrick Wing Kwan Ng, G. Zhang, J. Tang, and O. A. Dobre
Journal Paper Accepted for publication, IEEE Trans. Commun., Apr. 2020.

Abstract:

[J 33] Energy-Efficient Buffer-Aided Relaying Systems with Opportunistic Spectrum Access

K. Wang, Q. Wu, W. Chen, Y. Yang, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Trans. Green Commun. and Networking, Mar. 2020.

Abstract: In this paper, an energy-efficient cross-layer design framework is proposed for cooperative relaying networks, which takes into account the influence of spectrum utilization probability. Specifically, random arrival traffic is considered and an adaptive modulation and coding (AMC) scheme is adopted in the cooperative transmission system to improve the system performance. The average packet dropping rate of the relaybuffer is studied at first. With the packet dropping rate and stationary distribution of the system state, the closed-form expression of the delay is derived. Then the energy efficiency for relayassisted transmission is investigated, which takes into account the queueing process of the relay and the source. In this context, an energy efficiency optimization problem is formulated to determine the optimum strategy of power and time allocation for the relay-assisted cooperative system. Finally, the energy efficient switching strategy between the relay assisted transmission and the direct transmission is obtained, where packet transmissions have different delay requirements. In addition, energy efficient transmission policy with AMC is obtained. Numerical results demonstrate the effectiveness of the proposed design improving the energy efficiency.

[J 34] Resource Allocation for Secure Multi-UAV Communication Systems with Multi-Eavesdropper

R. Li, Z. Wei, L. Yang, Derrick Wing Kwan Ng, J. Yuan, and J. An
Journal Paper Accepted for publication, IEEE Trans. Commun., Mar. 2020.

Abstract: In this paper, we study the resource allocation and trajectory design for secure unmanned aerial vehicle (UAV)-enabled communication systems, where multiple multi-purpose UAV base stations are dispatched to provide secure communications to multiple legitimate ground users (GUs) in the existence of multiple eavesdroppers (Eves). Specifically, by leveraging orthogonal frequency division multiple access (OFDMA), active UAV base stations can communicate to their desired ground users via the assigned subcarriers while idle UAV base stations can serve as jammer simultaneously for communication security provisioning. To achieve fairness in secure communication, we maximize the average minimum secrecy rate per user by jointly optimizing the communication/jamming subcarrier allocation policy and the trajectory of UAVs, while taking into account the constraints on the minimum safety distance among multiple UAVs, the maximum cruising speed, the initial/final locations, and the existence of cylindrical no-fly zones (NFZs). The design is formulated as a mixed integer non-convex optimization problem which is generally intractable. Subsequently, a computationally-efficient iterative algorithm is proposed to obtain a suboptimal solution. Simulation results illustrate that the performance of the proposed iterative algorithm can significantly improve the average minimum secrecy rate compared to various baseline schemes.

[J 35] Joint Trajectory and Resource Allocation Design for Energy-Efficient Secure UAV Communication Systems

Y. Cai, Z. Wei, R. Li, Derrick Wing Kwan Ng, and J. Yuan
Journal Paper Accepted for publication, IEEE Trans. Commun., Mar. 2020.

Abstract: In this paper, we study the trajectory and resource allocation design for downlink energy-efficient secure unmanned aerial vehicle (UAV) communication systems, where an information UAV assisted by a multi-antenna jammer UAV serves multiple ground users in the existence of multiple ground eavesdroppers. The resource allocation strategy and the trajectory of the information UAV, and the jamming policy of the jammer UAV are jointly optimized for maximizing the system energy efficiency. The joint design is formulated as a non-convex optimization problem taking into account the quality of service (QoS) requirement, the security constraint, and the imperfect channel state information (CSI) of the eavesdroppers. The formulated problem is generally intractable. As a compromise approach, the problem is divided into two subproblems which facilitates the design of a low-complexity suboptimal algorithm based on alternating optimization approach. Simulation results illustrate that the proposed algorithm converges within a small number of iterations and demonstrate some interesting insights: (1) the introduction of a jammer UAV facilitates a highly flexible trajectory design of the information UAV which is critical to improving the system energy efficiency; (2) by exploiting the spatial degrees of freedom brought by the multi-antenna jammer UAV, our proposed design can focus the artificial noise on eavesdroppers offering a strong security mean to the system.

[J 36] Prospective Multiple Antenna Technologies for Beyond 5G

J. Zhang. E. Bjornson, M. Matthaious, Derrick Wing Kwan Ng, and D. J. Love
Journal Paper Accepted for publication, IEEE Trans. Commun., Mar. 2020.

Abstract: Multiple antenna technologies have attracted large research interest for several decades and have gradually made their way into mainstream communication systems. Two main benefits are adaptive beamforming gains and spatial multiplexing, leading to high data rates per user and per cell, especially when large antenna arrays are used. Now that multiple antenna technology has become a key component of the fifth-generation (5G) networks, it is time for the research community to look for new multiple antenna applications to meet the immensely higher data rate, reliability, and traffic demands in the beyond 5G era. We need radically new approaches to achieve orders-of-magnitude improvements in these metrics and this will be connected to large technical challenges, many of which are yet to be identified. In this survey paper, we present a survey of three new multiple antenna related research directions that might play a key role in beyond 5G networks: Cell-free massive multiple-input multiple-output (MIMO), beamspace massive MIMO, and intelligent reflecting surfaces. More specifically, the fundamental motivation and key characteristics of these new technologies are introduced. Recent technical progress is also presented. Finally, we provide a list of other prospective future research directions.

[J 37] Robust Trajectory and Transmit Power Optimization for Secure UAV-Enabled Cognitive Radio Networks

Y. Zhou, H. Zhou, F. Zhou, R. Q. Hu, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Trans. Commun., Mar. 2020.

Abstract: Cognitive radio is a promising technology to improve spectral efficiency. However, the secure performance of a secondary network achieved by using physical layer security techniques is limited by its transmit power and channel fading. In order to tackle this issue, a cognitive unmanned aerial vehicle (UAV) communication network is studied by exploiting the high flexibility of a UAV and the possibility of establishing line-of-sight links. The average secrecy rate of the secondary network is maximized by robustly optimizing the UAV’s trajectory and transmit power. Our problem formulation takes into account two practical inaccurate location estimation cases, namely, the worst case and the outage-constrained case. In order to solve those challenging non-convex problems, an iterative algorithm based on S-Procedure is proposed for the worst case while an iterative algorithm based on Bernstein-type inequalities is proposed for the outage-constrained case. The proposed algorithms can obtain effective suboptimal solutions of the corresponding problems. Our simulation results demonstrate that the algorithm under the outage-constrained case can achieve a higher average secrecy rate with a low computational complexity compared to that of the algorithm under the worst case. Moreover, the proposed schemes can improve the secure communication performance significantly compared to other benchmark schemes.

[J 38] Iterative Joint Channel Estimation, User Activity Tracking and Data Detection for FTN- NOMA Systems Supporting Random Access

W. Yuan, N. Wu, Q. Guo, Derrick Wing Kwan Ng, J. Yuan, and L. Hanzo
Journal Paper Accepted for publication, IEEE Trans. Commun., Feb. 2020.

Abtract: Given the requirements of increased data rate and massive connectivity in the Internet-of-things (IoT) applications of the fifth-generation communication systems (5G), nonorthogonal multiple access (NOMA) was shown to be capable of supporting more users than OMA. As a further potential enhancement, the faster-than-Nyquist (FTN) signaling is also capable of increasing the symbol rate. Since NOMA and FTN signaling impose non-orthogonalities from different perspectives, it is possible to achieve further increased spectral efficiency by exploiting both. Hence we investigate the FTN-NOMA uplink in the context of random access. Although random access schemes reduce the signaling overheads as well as latency, they require the base station to identify active users before performing data detection. As both inter-symbol and inter-user interferences exist, performing optimal detection requires a prohibitively high complexity. Moreover, in typical mobile communication environments, the channel envelope of users fluctuates violently, which imposes challenges on the receiver design. To tackle this problem, we propose a joint user activity tracking and data detection algorithm based on the factor graph framework, which relies on a sophisticated amalgam of expectation maximization (EM) and hybrid message passing algorithms. The complexity of the algorithm advocated only increases linearly with the number of active users. Our simulation results show that the proposed algorithm is effective in tracking user activity and detecting data symbols in dynamic random access systems.

[J 39] Dual-hop Relaying Communications Over Fisher-Snedecor F Fading Channels

P. Zhang, J. Zhang, K. P. Peppas, Derrick Wing Kwan Ng, and B. Ai
Journal Paper Accepted for publication, IEEE Trans. Commun., Feb. 2020.

[J 40] Joint User Association and Resource Allocation in the Uplink of Heterogeneous Network

A. Khalili, S. Akhlaghi, H. Tabassum, and Derrick Wing Kwan Ng
Journal Paper Accepted for publication, IEEE Wireless Commun. Letters, Jan. 2020.

[J 41] Receive Antenna Selection under Discrete Inputs: Approximation and Applications

C. Ouyang, S. Wu, C. Jiang, Derrick Wing Kwan Ng, and H. Yang
Journal Paper Accepted for publication, IEEE Trans. Commun., Jan. 2020.

[J 42] Multiuser MISO UAV Communications in Uncertain Environments with No-fly Zones: Robust Trajectory and Resource Allocation Design

D. Xu, Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Journal Paper Accepted for publication, IEEE Trans. Commun., Jan. 2020.

Abstract: In this paper, we investigate robust resource allocation algorithm design for multiuser downlink multiple-input single-output (MISO) unmanned aerial vehicle (UAV) communication systems, where we account for the various uncertainties that are unavoidable in such systems and, if left unattended, may severely degrade system performance. We jointly optimize the two-dimensional (2-D) trajectory and the transmit beamforming vector of the UAV for minimization of the total power consumption. The algorithm design is formulated as a nonconvex optimization problem taking into account the imperfect knowledge of the angle of departure (AoD) caused by UAV jittering, user location uncertainty, wind speed uncertainty, and polygonal no-fly zones (NFZs). Despite the non-convexity of the optimization problem, we solve it optimally by employing monotonic optimization theory and semidefinite programming relaxation which yields the optimal 2-D trajectory and beamforming policy. Since the developed optimal resource allocation algorithm entails a high computational complexity, we also propose a suboptimal iterative low-complexity scheme based on successive convex approximation to strike a balance between optimality and computational complexity. Our simulation results reveal not only the significant power savings enabled by the proposed algorithms compared to two baseline schemes, but also confirm their robustness with respect to UAV jittering, wind speed uncertainty, and user location uncertainty. Moreover, our results unveil that the joint presence of wind speed uncertainty and NFZs has a considerable impact on the UAV trajectory. Nevertheless, by counteracting the wind speed uncertainty with the proposed robust design, we can simultaneously minimize the total UAV power consumption and ensure a secure trajectory that does not trespass any NFZ.

[J 43] Physical-Layer Security in the Finite Blocklength Regime over Fading Channels

T.-X. Zheng, H.-M. Wang, Derrick Wing Kwan Ng, and J. Yuan
Journal Paper IEEE Trans. Wireless Commun., Jan. 2020.

[J 44] Secure Communication for Spatially Sparse Millimeter-Wave Massive MIMO Channel

J. Xu, W. Xu, Derrick Wing Kwan Ng, and A. L.Swindlehurst
Journal Paper IEEE Trans. Commun., vol. 68, no. 2, pp. 887-901, Feb. 2020.

[J 45] Conditional Capacity and Transmit Signal Design for SWIPT Systems with Multiple Nonlinear Energy Harvesting Receivers

R. Morsi, V. Jamali, A. Hagelauer, Derrick Wing Kwan Ng, and R. Schober
Journal Paper IEEE Trans. Commun., vol. 68, no. 1, pp. 582- 601, Jan. 2020.

[J 46] Robust Beamforming for Cellular Massive Internet-of-Things with SWIPT

Q. Qi, X. Chen, and Derrick Wing Kwan Ng
Journal Paper IEEE Trans. Signal Process., vol. 68, pp. 211- 224, 2020.

[J 47] Resource Allocation for Wireless-Powered Full-Duplex Relaying Systems with Non-Linear Energy Harvesting Efficiency

Z. Wei, S. Sun, X. Zhu, D. I. Kim, and Derrick Wing Kwan Ng
Journal Paper IEEE Trans. Veh. Technol., Oct. 2019

[J 48] On the Performance Gain of NOMA over OMA in Uplink Communication Systems

Z. Wei, Y. Lei, Derrick Wing Kwan Ng, J. Yuan, and L. Hanzo,
Journal Paper invited paper, accepted, IEEE Trans. Commun., Oct. 2019.

[J 49] Antenna Selection Strategy for Energy Efficiency Maximization in Uplink OFDMA Networks: A Multi-objective Approach,

A. Khalili, M. R. Mili, S. Parsaeefard, M. Rasti, and Derrick Wing Kwan Ng
Journal Paper IEEE Trans. Wireless Commun., Oct. 2019.

[J 50] Physical Layer Security in UAV Systems: Challenges and Opportunities

X. Sun, Derrick Wing Kwan Ng, Z. Ding, Y. Xu, and Z. Zhong
Journal Paper IEEE Wireless Communication Magazine, Sep. 2019.

Unmanned aerial vehicle (UAV) wireless communications has experienced an upsurge of interest in both military and civilian applications, due to its high mobility, low cost, on-demand deployment, and inherent line-of-sight air-to-ground channels. However, these benefits also make UAV wireless communication systems vulnerable to malicious eavesdropping attacks. In this article, we aim to examine the physical layer security issues in UAV systems. In particular, passive and active eavesdropping are two primary types of attack in UAV systems. We provide an overview on emerging techniques, such as trajectory design, resource allocation, and cooperative UAVs, to fight against both types of eavesdropping in UAV wireless communication systems. Moreover, the applications of non-orthogonal multiple access, multiple-input multiple-output, and millimeter-wave in UAV systems are also proposed to improve the system spectral efficiency and to guarantee security simultaneously. Finally, we discuss some potential research directions and challenges in terms of physical layer security in UAV systems

[J 51] C-RAN with Hybrid RF/FSO Fronthaul Links: Joint Optimization of Fronthaul Compression and RF Time Allocation

M. Najafi, V. Jamali, Derrick Wing Kwan Ng, and R. Schober
Journal Paper IEEE Trans. on Commun., Sep. 2019.

This paper considers the uplink of a cloud radio access network (C-RAN) comprised of several multi-antenna remote radio units (RUs) which compress the signals that they receive from multiple mobile users (MUs) and forward them to a CU via wireless fronthaul links. To enable reliable high rate fronthaul links, we employ a hybrid radio frequency (RF)/free space optical (FSO) system for fronthauling. Moreover, to strike a balance between complexity and performance, we consider three different quantization schemes at the RUs, namely perantenna vector quantization (AVQ), per-RU vector quantization (RVQ), and distributed source coding (DSC), two different RF fronthaul transmission modes, namely orthogonal transmission and non-orthogonal transmission, and two different detectors at the CU, namely the linear minimum mean square error detector and the optimal successive interference cancellation detector. For this network architecture, we investigate the joint optimization of the quantization noise covariance matrices at the RUs and the RF time allocation to the multiple-access and fronthaul links for rate region maximization. To this end, we formulate a unified weighted sum rate maximization problem valid for each possible combination of the considered quantization, RF fronthaul transmission, and detection schemes. To handle the non-convexity of the unified problem, we transform it into a bi-convex problem which facilitates the derivation of an efficient suboptimal solution using alternating convex optimization and golden section search. Moreover, by introducing a backoff parameter to reduce the probability of infeasibility, we generalize the proposed optimization framework to account for imperfect channel estimation. Our simulation results show that for each combination of the considered quantization, RF fronthaul transmission, and detection schemes, C-RAN with hybrid RF/FSO fronthauling can achieve a considerable sum rate gain compared to conventional systems employing pure FSO fronthauling, especially under unfavorable atmospheric conditions. In addition, employing a more sophisticated quantization scheme can significantly improve the system performance under adverse atmospheric conditions. In contrast, in clear weather conditions, when the FSO link capacity is high, the simple AVQ scheme performs close to the optimal DSC scheme. Furthermore, our simulation results suggest that the proposed algorithm can be adapted to the quality of the channel estimates by tuning the backoff parameter.

[J 52] Low-Cost Design of Massive Access for Cellular Internet of Things

G. Yu, X. Chen, and Derrick Wing Kwan Ng
Journal Paper IEEE Trans. on Commun., Jul. 2019.

In this paper, we investigate the issue of low-cost design of massive access for cellular internet of things (IoT) over spatially correlated Rician fading channels. Specifically, by exploiting a low-overhead transmission protocol, a base station (BS) equipped with a large-scale antenna array and low-resolution analog-to-digital converters (ADCs) is deployed to serve a massive number of IoT devices with low-complexity successive interference cancellation (SIC) receivers. We first analyze the impacts of the low-cost design on the system performance and derive closed-form expressions for uplink and downlink spectral efficiencies of the cellular IoT. Then, for alleviating the negative impacts of the low-cost design, we propose an algorithm allocating the time for channel estimation, uplink data transmission, and downlink data transmission in a data frame. Finally, extensive simulation results confirm the effectiveness of the proposed low-cost design for the cellular IoT.

[J 53] On the Power Leakage Problem in Millimeter-Wave massive MIMO with Lens Antenna Arrays

T. Xie, L. Dai, Derrick Wing Kwan Ng, and C.-B. Chae,
Journal Paper IEEE Trans. on Signal Processing, Jun. 2019.

The emerging millimeter-wave massive multiple-input multiple-output (MIMO) with lens antenna arrays, which is also known as “beamspace MIMO,” can effectively reduce the required number of power-hungry radio frequency (RF) chains. Therefore, it has been considered as a promising technique for the upcoming 5G communications and beyond. However, most current studies on beamspace MIMO have not taken into account the important power leakage problem in beamspace channels, which possibly leads to a significant degradation in the signal-to-noise ratio (SNR) and the system sum-rate. To this end, in this paper, we propose a beam-aligning precoding method to handle the power leakage problem. First, a phase shifter network (PSN) structure is proposed, which enables each RF chain in beamspace MIMO to select multiple beams to collect the leakage power. Then, a rotation-based precoding algorithm is designed based on the proposed PSN structure, which aligns the channel gains of the selected beams toward the same direction for maximizing the received SNR at each user. Furthermore, we reveal some system design insights by analyzing the sum-rate and energy efficiency (EE) of the proposed beam-aligning precoding method. In simulations, the proposed approach is found to achieve the near-optimal sum-rate performance compared with that of the ideal case of no power leakage, and obtains a higher EE than those of the existing schemes with either a linear or planar array.

[J 54] Generalized Wireless-Powered Communications: When to Activate Wireless Power Transfer?

Q. Wu, G. Zhang, Derrick Wing Kwan Ng, W. Chen, and R. Schober,
Journal Paper IEEE Trans. on Veh. Techn., Jun. 2019.

[J 55] A Novel Performance Tradeoff in Heterogeneous Networks: A Multi-objective Approach

M. R. Mili, A. Khalili, Derrick Wing Kwan Ng, and H. Steendam
Journal Paper IEEE WCL, May, 2019.

[J 56] Two-Way Hybrid Terrestrial-Satellite Relaying Systems: Performance Analysis and Relay Selection

W. Zeng, J. Zhang, Derrick Wing Kwan Ng, B. Ai, and Z. Zhong,
Journal Paper IEEE Trans. on Veh. Techn., May 2019.

[J 57] Enhanced Energy- Efficient Downlink Resource Allocation in Green Non-Orthogonal Multiple Access Systems

R Ruby, S Zhong, Derrick Wing Kwan Ng, K. Wu, V. C. M. Leung
Journal Paper Computer Communications, Elsevier, Apr. 2019.

[J 58] Cache-Aided Non-Orthogonal Multiple Access

L. Xiang, Derrick Wing Kwan Ng, X. Ge, Z. Ding, V. W.S. Wong, and R. Schober
Journal Paper accepted for publication, IEEE Journal of Selected Topics in Signal Processing-NOMA, Mar. 2019.

In this paper, we propose a cache-aided non-orthogonal multiple access (NOMA) scheme for spectrally efficient downlink transmission in the fifth-generation (5G) cellular networks. The proposed scheme not only reaps the benefits associated with NOMA and caching, but also exploits the data cached at the users for interference cancellation. As a consequence, caching can help to reduce the residual interference power, making multiple decoding orders at the users feasible. The resulting flexibility in decoding can be exploited for improved NOMA detection. We characterize the achievable rate region of cache-aided NOMA and derive the Pareto optimal rate tuples forming the boundary of the rate region. Moreover, we optimize cache-aided NOMA for minimization of the time required for completing file delivery. The optimal decoding order and the optimal transmit power and rate allocation are derived as functions of the cache status, the file sizes, and the channel conditions. Simulation results confirm that, compared to several baseline schemes, the proposed cache-aided NOMA scheme significantly expands the achievable rate region and increases the sum rate for downlink transmission, which translates into substantially reduced file delivery times

[J 59] NOMA for Hybrid MmWave Communication Systems with Beamwidth Control

Z. Wei, Derrick Wing Kwan Ng, and J. Yuan,
Journal Paper accepted for publication, IEEE Journal of Selected Topics in Signal Processing-NOMA, Feb. 2019.

In this paper, we propose a novel non-orthogonal multiple access (NOMA) scheme with beamwidth control for hybrid millimeter wave (mmWave) communication systems and study the resource allocation design to maximize the system energy efficiency. In particular, NOMA transmission allows more than one user to share a single radio frequency chain, which is beneficial to enhance the system energy efficiency. More importantly, the proposed beamwidth control can increase the number of served NOMA groups by widening the beamwidth which can further exploit the energy efficiency gain brought by NOMA. To this end, two beamwidth control methods, based on the conventional beamforming and the Dolph-Chebyshev beamforming, respectively, are proposed. We firstly characterize the main lobe power losses due to the two beamwidth control methods and propose an effective analog beamformer design to minimize the power loss. Then, we formulate the energy-efficient resource allocation design as a non-convex optimization problem which takes into account the minimum required user data rate. A NOMA user grouping algorithm based on the coalition formation game theory is developed and a low-complexity iterative digital precoder design is proposed to achieve a locally optimal solution utilizing the quadratic transformation. Simulation results verify the fast convergence and effectiveness of our proposed algorithms. In addition, our results demonstrate the superior energy efficiency achieved by our proposed beamwidth controlling NOMA scheme compared to the conventional orthogonal multiple access and NOMA schemes without beamwidth control.

[J 60] Multi-Antenna Covert Communications in Random Wireless Networks

T.-X. Zheng, H.-M. Wang, Derrick Wing Kwan Ng, and J. Yuan,
Journal Paper accepted for publication, IEEE Trans. Wireless Commun., Feb. 2019.

[J 61] Optimal 3D-Trajectory Design and Resource Allocation for Solar-Powered UAV Communication Systems

Y. Sun, D. Xu, Derrick Wing Kwan Ng, L. Dai, and R. Schober,
Journal Paper accepted for publication, IEEE Trans. Commun., Feb. 2019.

[J 62] Design of Non- Orthogonal Beamspace Multiple Access for Cellular Internet-of-Things

R. Jia, X. Chen, C. Zhong, Derrick Wing Kwan Ng, H. Lin, and Z. Zhang
Journal Paper accepted for publication, IEEE Journal of Selected Topics in Signal Processing-NOMA, Feb. 2019

In this paper, we study the problem of massive connections over limited radio spectrum for the cellular Internet-of-Things (IoT) in the fifth-generation (5G) wireless network. To address the challenging issues associated with channel state information (CSI) acquisition and beam design in the context of massive connections, we propose a new non-orthogonal beamspace multiple access framework. In particular, the user equipments (UEs) are non-orthogonal not only in the temporal-frequency domain, but also in the beam domain. We analyze the performance of the proposed non-orthogonal beamspace multiple access scheme, and derive an upper bound on the weighted sum rate in terms of channel conditions and system parameters. For further improving the performance, we propose three non-orthogonal transmit beam construction algorithms with different beamspace resolutions. Finally, extensive simulation results show that substantial performance gain can be obtained by the proposed non-orthogonal beamspace multiple access scheme over the baseline ones.

[J 63] Physical-Layer Network Coding Based Decoding Scheme for Random Access

Z. Sun, L. Yang, J. Yuan, andDerrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Trans. Veh. Techno., Jan. 2019.

[J 64] Secure Massive MIMO Communication with Low-resolution DACs

J. Xu, W. Xu, J. Zhu, Derrick Wing Kwan Ng, and A. L. Swindlehurst,
Journal Paper accepted for publication, IEEE Trans. Commun., Jan. 2019.

[J 65] Joint Channel Parameter Estimation in Multi-cell Massive MIMO System

X. Wei, W. Peng, D. Chen, Derrick Wing Kwan Ng, and T. Jiang
Journal Paper accepted for publication, IEEE Trans. Commun., Jan. 2019.

[J 66] Online Polices for Throughput Maximization of Energy-Constrained Wireless-Powered Communication Systems

X. Li, X. Zhou, C. Sun, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Trans. Wireless Commun., Dec. 2018.

[J 67] On the Design of Massive Non-Orthogonal Multiple Access with Imperfect Successive Interference Cancellation

X. Chen, R. Jia, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Trans. Commun., Nov. 2018.

[J 68] Delay Minimization for NOMA-MEC Offloadings

Z. Ding, Derrick Wing Kwan Ng, R. Schober, and H. V. Poor,
Journal Paper accepted for publication, IEEE Signal Processing Letters, Oct. 2018.

[J 69] Multi-Beam NOMA for Hybrid mmWave Systems

Z. Wei, L. Zhao, J. Guo, Derrick Wing Kwan Ng, and J. Yuan
Journal Paper accepted for publication, IEEE Trans. Commun., Oct. 2018

[J 70] Fundamentals of Wireless Information and Power Transfer: From RF Energy Harvester Models to Signal and System Designs

B. Clerckx, R. Zhang, R. Schober, Derrick Wing Kwan Ng, D. I. Kim, and H. V. Poor,
Journal Paper IEEE JSAC, vol. 37, no. 1, pp. 4-33, Jan. 2019.

[J 71] The Application of Relay to Massive Non-Orthogonal Multiple Access

X. Chen, R. Jia, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Trans. Commun., Jun. 2018.

Abstract: — This paper considers the application of relay to enhance the performance of massive non-orthogonal multiple access (NOMA) systems and solve the challenge of channel state information (CSI) acquisition in the case of a massive number of users. Firstly, we design a general framework for a multiple-relay aided massive NOMA system. Then, we analyze the performance of the multiple-relay aided massive NOMA system, and derive a closed-form expression for a lower bound on the spectral efficiency. In particular, we reveal the impact of system parameters on the spectral efficiency via asymptotic analysis in three important scenarios, e.g., a large number of antennas at the base station (BS), a high transmit power at the BS or the relays, and a large number of relays. To further improve the spectral efficiency in the context of massive access, we propose two effective schemes to optimize the transmit power at the BS and relays, respectively. Finally, extensive simulation results validate the effectiveness of the proposed multiple-relay aided massive NOMA scheme

[J 72] Robust Trajectory and Transmit Power Design for Secure UAV Communications

M. Cui, G. Zhang, Q. Wu, Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Trans. Veh. Tech., Jun. 2018.

Abstract: — In this paper, we investigate the system performance of a multi-cell multi-user (MU) hybrid mil- limeter wave (mmWave) communications in a multiple-input multiple-output (MIMO) network. Due to the reuse of pilot symbols among different cells, the performance of channel estimation is expected to be degraded by pilot contamination, which is considered as a fundamental performance bottleneck of conventional multi-cell MU massive MIMO networks. To analyze the impact of pilot contamination to the system performance, we first derive the closed-form approximation of the normalized mean squared error (MSE) of the channel estimation algorithm proposed in [1] over Rician fading channels. Our analytical and simulation results show that the channel estimation error incurred by the impact of pilot contamination and noise vanishes asymptotically with an increasing number of antennas equipped at each radio frequency (RF) chain at the desired BS. Furthermore, by adopting zero-forcing (ZF) precoding in each cell for downlink transmission, we derive a tight closed-form approximation of the average achievable rate per user. Our results unveil that the intra-cell interference and inter-cell interference caused by pilot contamination over Rician fading channels can be mitigated effectively by simply increasing the number of antennas equipped at the desired BS.

[J 73] Multi-Quality Multicast Beamforming with Scalable Video Coding

C. Guo, Y. Cui, Derrick Wing Kwan Ng, and Z. Liu
Journal Paper accepted for publication, IEEE Trans. Commun., May 2018.

Abstract: — In this paper, we consider multi-quality multicast beamforming of a video stream from a multi- antenna base station (BS) to multiple single-antenna users receiving different qualities of the same video stream, via scalable video coding (SVC). Leveraging the layered structure of SVC and exploiting superposition coding (SC) as well as successive interference cancelation (SIC), we propose a layer-based multi-quality multicast beamforming scheme. To reduce the computational complexity, we also propose a quality-based multi-quality multicast beamforming scheme, which further utilizes the layered structure of SVC and quality information of all users. Under each scheme, for given quality requirements of all users, we formulate the corresponding optimal beamforming design as a non-convex power minimization problem, and obtain a globally optimal solution for a class of special cases as well as a locally optimal solution for the general case. Then, we show that the minimum total transmission power of the layer- based power minimization problem is the same as that of the quality-based power minimization problem, although the latter incurs a lower computational complexity. Next, we consider the optimal joint layer selection and quality-based multi-quality multicast beamforming design to maximize the total utility representing the satisfaction with the received video quality for all users under a given maximum transmission power budget, which is NP-hard in general. Based on the optimal solution of the quality- based power minimization problem, we develop a greedy algorithm to obtain a near optimal solution. Finally, numerical results show that the proposed solutions achieve better performance than existing solutions

[J 74] Joint Beamforming and Power Allocation in Downlink NOMA Multiuser MIMO Networks

X. Sun, N. Yang, S. Yan, Z. Ding, Derrick Wing Kwan Ng, C. Shen, and Z. Zhong,
Journal Paper accepted for publication, IEEE Trans. Wireless Commun., May 2018.

Abstract: —

[J 75] Multi-cell Hybrid Millimeter Wave Systems: Pilot Contamination and Interference Mitigation

L. Zhao, Derrick Wing Kwan Ng, Z. Wei, J. Yuan, and M. Reed
Journal Paper accepted for publication, IEEE Trans. Commun., May 2018.

Abstract: —

[J 76] Resource Allocation in NOMA Virtualized Wireless Networks under Statistical Delay Constraints

M. Sinaie, Derrick Wing Kwan Ng, and E. A. Jorswieck,
Journal Paper accepted for publication, IEEE Wireless Commun. Letter, May 2018.

Abstract: —

[J 77] Secure Routing with Power Optimization for Ad-hoc Networks

H.-M. Wang, Y. Zhang, Derrick Wing Kwan Ng, and M. H. Lee,
Journal Paper accepted for publication, IEEE Trans. Commun., Apr. 2018.

Abstract: —

[J 78] Robust and Secure Resource Allocation for Full-Duplex MISO Multicarrier NOMA Systems

Y. Sun, Derrick Wing Kwan Ng, J. Zhu, and R. Schober,
Journal Paper accepted for publication, IEEE Trans. Commun., Apr. 2018.

Abstract: —

[J 79] Secure Video Streaming in Heterogeneous Small Cell Networks with Untrusted Cache Helpers

L. Xiang, Derrick Wing Kwan Ng, R. Schober, and V. W.S. Wong
Journal Paper accepted for publication, IEEE Trans. Wireless Commun., Jan. 2018.

Abstract: — This paper studies secure video streaming in cache-enabled small cell networks, where some of the cache-enabled small cell base stations (BSs) helping in video delivery are untrusted. Unfavorably, caching improves the eavesdropping capability of these untrusted helpers as they may intercept both the cached and the delivered video files. To address this issue, we propose joint caching and scalable video coding (SVC) of video files to enable secure cooperative multiple-input multiple-output (MIMO) transmission and, at the same time, exploit the cache memory of both the trusted and untrusted BSs for improving the system performance. Considering imperfect channel state information (CSI) at the transmitters, we formulate a two- timescale non-convex mixed-integer robust optimization problem to minimize the total transmit power required for guaranteeing the quality of service (QoS) and secrecy during video streaming. We develop an iterative algorithm based on a modified generalized Benders decomposition (GBD) to solve the problem optimally, where the caching and the cooperative transmission policies are determined via offline (long-timescale) and online (short-timescale) optimization, respectively. Furthermore, inspired by the optimal algorithm, a low- complexity suboptimal algorithm based on a greedy heuristic is proposed. Simulation results show that the proposed schemes achieve significant gains in power efficiency and secrecy performance compared to several baseline schemes

[J 80] Joint Pilot and Payload Power Control for Uplink MIMO-NOMA with MRC-SIC Receivers

Z. Wei, Derrick Wing Kwan Ng, and J. Yuan
Journal Paper accepted for publication, IEEE Commun. Lett., Jan. 2018.

Abstract: — This letter proposes a joint pilot and payload power allocation (JPA) scheme to mitigate the error propagation prob- lem for uplink multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) systems. A base station equipped with a maximum ratio combining and successive interference can- cellation (MRC-SIC) receiver is adopted for multiuser detection. The average signal-to-interference-plus-noise ratio (ASINR) of each user during the MRC-SIC decoding is analyzed by taking into account the error propagation due to the channel estimation error. Furthermore, the JPA design is formulated as a non- convex optimization problem to maximize the minimum weighted ASINR and is solved optimally with geometric programming. Simulation results confirm the developed performance analysis and show that our proposed scheme can effectively alleviate the error propagation of MRC-SIC and enhance the detection performance, especially for users with moderate energy budgets

[J 81] Spatial Modulation Assisted Multi-Antenna Non-Orthogonal Multiple Access

C. Zhong, X. Hu, X. Chen, Derrick Wing Kwan Ng, and Z. Zhang
Journal Paper accepted for publication, IEEE Commun. Mag., Special Issue on Non-Orthogonal Multiple Access for 5G, Dec. 2017

Abstract: —

[J 82] Power-Efficient and Secure WPCNs with Hardware Impairments and Non-Linear EH Circuit

E. Boshkovska, Derrick Wing Kwan Ng, L. Dai, and R. Schober
Journal Paper accepted for publication, IEEE Trans. Commun., Dec. 2017

Abstract: — In this paper, we design a robust resource allocation algorithm for a wireless-powered communication network (WPCN) taking into account residual hardware impairments (HWIs) at the transceivers, the imperfectness of the channel state information, and the non-linearity of practical radio frequency energy harvesting circuits. In order to ensure power-efficient secure communication, physical layer security techniques are exploited to deliberately degrade the channel quality of a multipleantenna eavesdropper. The resource allocation algorithm design is formulated as a non-convex optimization problem for minimization of the total power consumption in the network, while guaranteeing the quality of service of the information receivers in terms of secrecy rate. The globally optimal solution of the optimization problem is obtained via a two-dimensional search and semidefinite programming relaxation. To strike a balance between computational complexity and system performance, a low-complexity iterative suboptimal resource allocation algorithm is also proposed. Numerical results demonstrate that both the proposed optimal and suboptimal schemes can significantly reduce the total system power consumption required for guaranteeing secure communication, and unveil the impact of HWIs on the system performance: (1) Residual HWIs create a system performance bottleneck in WPCN in the high transmit/receive power regimes; (2) increasing the number of transmit antennas can effectively reduce the power consumption of wireless power transfer and alleviate the performance degradation due to residual HWIs; (3) imperfect CSI exacerbates the impact of residual HWIs which increases the power consumption of both wireless power and wireless information transfer.

[J 83] Fully Non-Orthogonal Communication for Massive Access

X. Chen, Z. Zhang, C. Zhong, R. Jia, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Trans. Commun., Nov. 2017

Abstract: — To achieve spectral-efficient massive access in future wireless networks, this paper proposes a com- prehensive fully non-orthogonal communication framework. Firstly, we design a fully non-orthogonal communication scheme which consists of non-orthogonal channel estimation and non-orthogonal mul- tiple access. Then, we analyze the performance of the proposed fully non-orthogonal communication, and derive a tight lower bound on the spectral efficiency in terms of key system parameters and channel conditions. Meanwhile, several novel insights for spectral efficiency are studied via asymptotic analysis in three important cases, i.e., a large number of base station (BS) antennas, a high BS transmit power, and perfect channel state information (CSI) at the BS. Finally, we optimize the performance of the proposed fully non-orthogonal communication and present two simple but efficient optimization algorithms for maximizing the weighted sum of spectral efficiency. Extensive simulation results validate the effectiveness of the proposed schemes

[J 84] Optimal Energy Efficiency Fairness of Nodes in Wireless Powered Communication Networks

J. Zhang, Q. Zhou, Derrick Wing Kwan Ng, and M. Jo,
Journal Paper accepted for publication, Sensors, MPDI, Sep. 2017.

Abstract: —

[J 85] Cache-Enabled Physical Layer Security for Video Streaming in Backhaul-Limited Cellular Networks

L. Xiang, Derrick Wing Kwan Ng, R. Schober, and V. W.S. Wong
Journal Paper accepted for publication, IEEE Trans. on Wireless Commun., Oct. 2017.

Abstract: —

[J 86] A Tone-based AoA Estimation and Multiuser Precoding for Millimeter Wave Massive MIMO

L. Zhao, G. Geraci, T. Yang, Derrick Wing Kwan Ng, and J. Yuan
Journal Paper accepted for publication, IEEE Trans. on Commun., Aug. 2017.

Abstract: — In this paper, we investigate channel estimation and multiuser (MU) downlink transmission of a time division duplex (TDD) massive multiple-input multiple-output (MIMO) system in millimeter wave (mmWave) channels. \color{black}We propose a tone-based linear search algorithm to facilitate the estimation of angle-of-arrivals (AoAs) of the strongest line-of-sight (SLOS) channel component as well as scattering components of the users at the base station (BS). Based on the estimated AoAs, we reconstruct the SLOS component and scattering components of the users for downlink transmission. We then derive the achievable rates of maximum-ratio transmission (MRT) and zero-forcing (ZF) precoding based on the SLOS component and the SLOS-plus-scattering components (SLPS), respectively. Taking into account the impact of pilot contamination, our analysis and simulation results show that the SLOS-based MRT can achieve higher data rate than that of the traditional pilot-aided-CSI-based (PAC-based) MRT, under the same mean square errors (MSE) of channel estimation. As for ZF precoding, the achievable rates of the SLPS-based and the PAC-based are identical. Furthermore, we quantify the achievable rate degradation of the SLOS-based MRT precoding caused by phase quantization errors in the large number of antennas regime. We show that the impact of phase quantization errors on the considered systems cannot be mitigated by increasing the number of antennas and therefore the resolutions of radio frequency phase shifters is critical for the design of efficient mmWave massive MIMO systems.

[J 87] Comment on “Optimal Precoding for a QoS Optimization Problem in Two-user MISO-NOMA Downlink

Z. Chen, Z. Ding, P. Xu, X. Dai, J. Xu, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Comm. Lett., May 2017.

Abstract: —

[J 88] Exploiting Multiple- Antenna Techniques for Non-Orthogonal Multiple Access

Q. Yang, H.-M. Wang, Derrick Wing Kwan Ng, and M. H. Lee
Journal Paper accepted for publication, IEEE JSAC SI in Non-Orthogonal Multiple Access for 5G Systems, Apr. 2017.

Abstract: —

[J 89] NOMA in Downlink SDMA with Limited Feedback: Performance Analysis and Optimization

X. Chen, Z. Zhang, C. Zhong, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE JSAC SI in Non-Orthogonal Multiple Access for 5G Systems, Apr. 2017.

Abstract: —

[J 90] Low-Complexity MIMO Precoding for Finite-Alphabet Signals

Y. Wu, C.-K. Wen, Derrick Wing Kwan Ng, R. Schober, and A. Lozan,
Journal Paper IEEE Trans. Wireless Commun.IEEE Trans. Wireless Commun., vol. 16, no. 7, pp. 4571-4584, Jul. 2017.

Abstract: —

[J 91] Robust Beamforming Design in C-RAN with Sigmoidal Utility and Capacity-Limited Backhaul

Z. Wang, Derrick Wing Kwan Ng, V. W.S. Wong, and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol. 16, no. 9, pp. 5583-5598, Sep. 2017.

Abstract: —

[J 92] Capacity of the Two-Hop Relay Channel with Wireless Power Transfer from Relay to Source and Processing Cost

N. Zlatanov, Derrick Wing Kwan Ng, and R. Schober
Journal Paper accepted, IEEE Trans. Wireless Commn., vol. 65, no. 3, pp. 1077-1091, Mar. 2017.

Abstract: —

[J 93] Joint Optimization of Analog Beam and User Scheduling for Millimeter Wave Communications

S. He, Y. Wu, Derrick Wing Kwan Ng , and Y. Huang
Journal Paper accepted, IEEE Communications Letters, Aug. 2017.

Abstract: — Millimeter wave (mmWave) technology is one of the promising candidates for future wireless communication systems to provide gigabit data rates to meet the stringent quality of service requirements of multimedia applications. Analog beam selection and user scheduling are two key problems for realizing multiuser mmWave communication in practical systems. In this letter, we focus on the joint optimization of analog beam selection and user scheduling based on limited effective channel state information. Two codebook based effective methods are developed to address the problem of interest. Numerical results show that the developed suboptimal methods achieve a considerable achievable sum rate performance of the optimal exhaustive search method, but with a fairly low computational complexity.

[J 94] Cross-Layer Optimization of Fast Video Delivery in Cache- and Buffer-Enabled Relaying Networks

L. Xiang, Derrick Wing Kwan Ng, T. Islam, R. Schober, V. W.S. Wong, and J. Wang,
Journal Paper accepted, IEEE Trans. Veh. Tech., Jul. 2017.

Abstract: —

[J 95] Energy Efficiency Evaluation of Multi-tier Cellular Uplink Transmission under Maximum Power Constraint

J. Zhang, L. Xiang, Derrick Wing Kwan Ng, M. Jo, and M. Chen
Journal Paper accepted, IEEE Trans. Wireless Commun. Aug. 2017.

Abstract: —

[J 96]
Spectral and Energy Efficient Wireless Powered IoT Networks: NOMA or TDMA?

Q. Wu, Wen Chen, Derrick Wing Kwan Ng, and R. Schober
Journal Paper accepted for publication, TVT, Jan. 2018.

Abstract: —

[J 97] Energy-Efficient Resource Allocation in Buffer-Aided Wireless Relay Networks

J. Hajipour, J. M. Niya, and Derrick Wing Kwan Ng
Journal Paper accepted, IEEE Trans. Wireless Commun. Jun. 2017.

Abstract: —

[J 98] Optimal Resource Allocation for Power-Efficient MC-NOMA with Imperfect Channel State Information

Z. Wei, Derrick Wing Kwan Ng, and J. Yuan, and H.-M. Wang
Journal Paper accepted, IEEE Trans. Commun. May. 2017.

Abstract: —In this paper, we study power-efficient resource allocation for multicarrier non-orthogonal multiple access (MC-NOMA) systems. The resource allocation algorithm design is formulated as a non-convex optimization problem which jointly designs the power allocation, rate allocation, user scheduling, and successive interference cancellation (SIC) decoding policy for minimizing the total transmit power. The proposed framework takes into account the imperfection of channel state information at transmitter (CSIT) and quality of service (QoS) requirements of users. To facilitate the design of optimal SIC decoding policy on each subcarrier, we define a channel-to-noise ratio outage threshold. Subsequently, the considered non-convex optimization problem is recast as a generalized linear multiplicative programming problem, for which a globally optimal solution is obtained via employing the branch-and-bound approach. The optimal resource allocation policy serves as a system performance benchmark due to its high computational complexity. To strike a balance between system performance and computational complexity, we propose a suboptimal iterative resource allocation algorithm based on difference of convex programming. Simulation results demonstrate that the suboptimal scheme achieves a close-tooptimal performance. Also, both proposed schemes provide significant transmit power savings than that of conventional orthogonal multiple access (OMA) schemes.

[J 99] Robust Chance-Constrained Optimization for Power-Efficient and Secure SWIPT Systems

T. A. Le, Q.-T. Vien, H. X. Nguyen, Derrick Wing Kwan Ng, and R. Schober
Journal Paper accepted, IEEE Trans. Green Commun. and Netw. , May. 2017.

Abstract: — In this paper, we propose beamforming schemes to simultaneously transmit data securely to multiple information receivers (IRs) while transferring power wirelessly to multiple energy-harvesting receivers (ERs). Taking into account the imperfection of the instantaneous channel state information, we introduce a chance-constrained optimization problem to minimize the total transmit power while guaranteeing data transmission reliability, data transmission security, and power transfer reliability. As the proposed optimization problem is non-convex due to the chance constraints, we propose two robust reformulations of the original problem based on safe-convex-approximation techniques. Subsequently, applying semidefinite programming relaxation, the derived robust reformulations can be effectively solved by standard convex optimization packages. We show that the adopted relaxation is tight and thus the globally optimal solutions of the reformulated problems can be recovered. Simulation results confirm the superiority of the proposed approaches in guaranteeing transmission security compared to a baseline scheme.

[J 100] Energy-Efficient D2D Overlaying Communications with Spectrum-Power Trading

Q. Wu, G. Y. Li, W. Chen, and Derrick Wing Kwan Ng
Journal Paper accepted, IEEE Trans. Wireless Comm., Apr. 2017.

Abstract: — In this paper, we investigate device-to-device (D2D) overlaying communications with spectrum- power trading where D2D users (DUs) consume transmit power to relay cell-edge cellular users (CUs) for uplink transmission in exchange for bandwidth from CUs for D2D communications. The proposed spectrum-power trading aims at exploiting individual disparities from both the spectrum and the power perspectives. Our goal is to maximize the weighted sum EE (WSEE) of DUs via a joint D2D relay selection, bandwidth allocation, and power allocation while guaranteeing the quality of service (QoS) of each CU. Specifically, we study WSEE maximization problems for two different cases, i.e., public- interest DUs and self-interest DUs, depending on whether the DUs are willing to share their obtained bandwidth with each other or not. For the case of public-interest DUs, we show that for a given D2D relay selection, the objective function of the WSEE maximization problem in a fractional form can be transformed into a subtractive-form that is more tractable based on the fractional programming theory. To perform D2D relay selection, we first reveal an important property, which connects the WSEE with both the system-centric EE and the fairness-centric EE . Based on this insight, the D2D relay selection problem can be cast into a minimum weighted bipartite matching problem. For the case of self-interest DUs, we show that the corresponding problem can be also solved with optimality by the algorithm proposed for the previous case. Simulation results demonstrate the effectiveness of the proposed algorithm.

[J 101] An Overview of Sustainable Green 5G Networks

Q. Wu, G. Y. Li, W. Chen, Derrick Wing Kwan Ng, and R. Schober
Journal Paper accepted, IEEE Comm. Mag. , Mar. 2017.

Abstract: — The stringent requirements of a 1,000 times increase in data traffic and one millisecond round trip latency have made limiting the potentially tremendous ensuing energy consumption one of the most challenging problems for the design of the upcoming fifth-generation (5G) networks. To enable sustainable 5G networks, new technologies have been proposed to improve the system energy efficiency and alternative energy sources are introduced to reduce our dependence on traditional fossil fuels. In particular, various 5G techniques target the reduction of the energy consumption without sacrificing the quality-of-service. Meanwhile, energy harvesting technologies, which enable communication transceivers to harvest energy from various renewable resources and ambient radio frequency signals for communi- cation, have drawn significant interest from both academia and industry. In this article, we provide an overview of the latest research on both green 5G techniques and energy harvesting for communication. In addition, some technical challenges and potential research topics for realizing sustainable green 5G networks are also identified.

[J 102] Multi-user Precoding and Channel Estimation for Hybrid Millimeter Wave Systems

L. Zhao, Derrick Wing Kwan Ng, and J. Yuan
Journal Paper accepted, IEEE JSAC 2017, Mar. 2017.

Abstract: — In this paper, we develop a low-complexity channel estimation for hybrid millimeter wave (mmWave) systems, where the number of radio frequency (RF) chains is much less than the number of antennas equipped at each transceiver. The proposed mmWave channel estimation algorithm first exploits multiple frequency tones to estimate the strongest angle-of-arrivals (AoAs) at both base station (BS) and user sides for the design of analog beamforming matrices. Then all the users transmit orthogonal pilot symbols to the BS along the directions of the estimated strongest AoAs in order to estimate the channel. The estimated channel will be adopted to design the digital zero-forcing (ZF) precoder at the BS for the multi-user downlink transmission. The proposed channel estimation algorithm is applicable to both nonsparse and sparse mmWave channel environments. Furthermore, we derive a tight achievable rate upper bound of the digital ZF precoding with the proposed channel estimation algorithm scheme. Our analytical and simulation results show that the proposed scheme obtains a considerable achievable rate of fully digital systems, where the number of RF chains equipped at each transceiver is equal to the number of antennas. Besides, by taking into account the effect of various types of errors, i.e., random phase errors, transceiver analog beamforming errors, and equivalent channel estimation errors, we derive a closed-form approximation for the achievable rate of the considered scheme. We illustrate the robustness of the proposed channel estimation and multi-user downlink precoding scheme against the system imperfection.

[J 103] Outage Performance for Cooperative NOMA Transmission with an AF Relay

X. Liang, Y. Wu Derrick Wing Kwan Ng, Y. Zuo, S. Jin, and H. Zhu
Journal Paper accepted, IEEE Com. Lett., Mar. 2017.

Abstract: — This letter studies the outage performance of cooperative non-orthogonal multiple access (NOMA) network with the help of an amplify-and-forward relay. An accurate closed-form approximation for the exact outage probability is derived. Based on this, the asymptotic outage probability is investigated, which shows that cooperative NOMA achieves the same diversity order and the superior coding gain compared to cooperative orthogonal multiple access. It is also revealed that when the transmit power of relay is smaller than that of the base station, the outage performance improves as the distance between the relay and indirect link user decreases.

[J 104] Analysis and Design of Secure Massive MIMO Systems in the Presence of Hardware Impairments

J. Zhu, Derrick Wing Kwan Ng, N. Wang, R. Schober, and V. K. Bhargava
Journal Paper accepted, IEEE Trans. Wireless Commun., Jan. 2017.

Abstract: — To keep the hardware costs of future communications systems manageable, the use of low-cost hardware components is desirable. This is particularly true for the emerging massive multiple-input multiple-output (MIMO) systems which equip base stations (BSs) with a large number of antenna elements. However, low-cost transceiver designs will further accentuate the hardware impairments which are present in any practical communication system. In this paper, we investigate the impact of hardware impairments on the secrecy performance of downlink massive MIMO systems in the presence of a passive multiple-antenna eavesdropper. Thereby, for the BS and the legitimate users, the joint effects of multiplicative phase noise, additive distortion noise, and amplified receiver noise are taken into account, whereas the eavesdropper is assumed to employ ideal hardware. We derive a lower bound for the ergodic secrecy rate of a given user when matched filter (MF) data precoding and artificial noise (AN) transmission are employed at the BS. Based on the derived analytical expression, we investigate the impact of the various system parameters on the secrecy rate and optimize both the pilot sets used for uplink training and the AN precoding. Our analytical and simulation results reveal that 1) the additive distortion noise at the BS may be beneficial for the secrecy performance, especially if the power assigned for AN emission is not sufficient; 2) all other hardware impairments have a negative impact on the secrecy performance; 3) {\textcolor{blue}{despite their susceptibility to pilot interference in the presence of phase noise}}, so-called spatially orthogonal pilot sequences are preferable unless the phase noise is very strong; 4) the proposed generalized null-space (NS) AN precoding method can efficiently mitigate the negative effects of phase noise.

[J 105] Rate-Power-Interference Optimization in Underlay OFDMA CRNs with Imperfect CSI

M. R. Mili, L. Musavian, and Derrick Wing Kwan Ng
Journal Paper accepted, IEEE Communications Letters, Jan. 2017.

Abstract: —Achieving higher transmission rate while reducing transmission power and induced interference on neighboring receivers is deemed necessary for the advancement of future generation networks and is particularly challenging since these directions could be conflicting in nature. This letter adopts a multiobjective optimization (MOOP) approach to settle the tradeoffs between these three conflicting objectives in orthogonal frequency-division multiple access (OFDMA)-based cognitive radio networks (CRNs). Besides, unlike most of the work in the literature that studied the imperfect channel side information (CSI) of only the link between secondary transmitter and primary receiver, the problem formulation takes into account the imperfect CSI of cross links between secondary and primary which makes the formulated MOOP difficult to solve since traditional water-filling-in-time solution does not directly apply to this problem. Hence, to solve this MOOP, a dummy power allocation is first used and then obtained MOOP is solved by using a weighted Tchebycheff method

[J 106] Robust Resource Allocation for MIMO Wireless Powered Communication Networks Based on a Non-linear EH Model

E. Boshkovska, Derrick Wing Kwan Ng, N. Zlatanov, A. Koelpin, and R. Schober
Journal Paper accepted for publication, IEEE Transactions on Communications, Jan. 2017.

Abstract: In this paper, we consider a multiple-input multiple-output wireless powered communication network (MIMO-WPCN), where multiple users harvest energy from a dedicated power station in order to be able to transmit their information signals to an information receiving station. Employing a practical non-linear energy harvesting (EH) model, we propose a joint time allocation and power control scheme, which takes into account the uncertainty regarding the channel state information (CSI) and provides robustness against imperfect CSI knowledge. In particular, we formulate two non-convex optimization problems for different objectives, namely system sum throughput maximization and maximization of the minimum individual throughput across all wireless powered users. To overcome the non-convexity, we apply several transformations along with a one-dimensional search to obtain an efficient resource allocation algorithm. Numerical results reveal that a significant performance gain can be achieved when the resource allocation is designed based on the adopted non-linear EH model instead of the conventional linear EH model. Besides, unlike a non-robust baseline scheme designed for perfect CSI, the proposed resource allocation schemes are shown to be robust against imperfect CSI knowledge.

[J 107] Optimal Joint Power and Subcarrier Allocation for Full-Duplex Multicarrier Non-Orthogonal Multiple Access Systems

Y. Sun, Derrick Wing Kwan Ng, Z. Ding, and R. Schober
Journal Paper accepted for publication, IEEE Transactions on Communications, Jan. 2017.

Abstract: In this paper, we investigate resource allocation algorithm design for multicarrier non-orthogonal multiple access (MC-NOMA) systems employing a full-duplex (FD) base station (BS) for serving multiple half-duplex (HD) downlink (DL) and uplink (UL) users simultaneously. The proposed algorithm is obtained from the solution of a non-convex optimization problem for the maximization of the weighted sum system throughput. We apply monotonic optimization to develop an optimal joint power and subcarrier allocation policy. The optimal resource allocation policy serves as a system performance benchmark due to its high computational complexity. Furthermore, a suboptimal iterative scheme based on successive convex approximation is proposed to strike a balance between computational complexity and optimality. Our simulation results reveal that the proposed suboptimal algorithm achieves a close-to-optimal performance. In addition, FD MC-NOMA systems employing the proposed resource allocation algorithms provide a substantial system throughput improvement compared to conventional HD multicarrier orthogonal multiple access (MC-OMA) systems and other baseline schemes. Also, our results unveil that FD MC-NOMA systems enable a fairer resource allocation compared to traditional HD MC-OMA systems

[J 108] A Survey of Downlink Non-orthogonal Multiple Access for 5G Wireless Communication Networks

Z. Wei, J. Yuan, Derrick Wing Kwan Ng, M. Elkashlan, and Z. Ding
Journal Paper accepted for publication, ZTE Communications, Sep. 2016.

Abstract: Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for the next generation cellular communication networks. In this paper, we first discuss a simple NOMA model with two users served by a single-carrier simultaneously to illustrate its basic principles. Then, a more general model with multicarrier serving an arbitrary number of users on each subcarrier is also discussed. An overview of existing works on performance analysis, resource allocation, and multiple-input multiple-output NOMA are summarized and discussed. Furthermore, we discuss the key features of NOMA and its potential research challenges.

[J 109] A Survey on Multiple Antenna Techniques for Physical Layer Security

X. Chen, Derrick Wing Kwan Ng, W. Gerstacker, and H.-H. Chen
Journal Paper accepted for publication, IEEE IEEE Communications Surveys and Tutorials, Sep. 2016.

Abstract: As a complement to high-layer encryption techniques, physical layer security has been widely recognised as a promising way to enhance wireless security by exploiting the characteristics of wireless channels, including fading, noise, and interference. In order to enhance the received signal power at legitimate receivers and impair the received signal quality at eavesdroppers simultaneously, multiple-antenna techniques have been proposed for physical layer security to improve secrecy performance via exploiting spatial degrees of freedom. This article provides a comprehensive survey on various multipleantenna techniques in physical layer security, with an emphasis on transmit beamforming designs for multiple-antenna nodes. Specifically, we provide a detailed investigation on multipleantenna techniques for guaranteeing secure communications in point-to-point systems, dual-hop relaying systems, multiuser systems, and heterogeneous networks. Finally, future research directions and challenges are identified.

[J 110] Energy-Efficient Small Cell with Spectrum-Power Trading

Q. Wu, G. Li, W. Chen, and Derrick Wing Kwan Ng
Journal Paper accepted for publication, IEEE Journal on Selected Areas in Communications - Series on Green Communications and Networking (Issue 3), Aug. 2016.

Abstract: In this paper, we investigate spectrum-power trading between a small cell (SC) and a macro cell (MC), where the SC consumes power to serve the macro cell users (MUs) in exchange for some bandwidth from the MC. Our goal is to maximize the system energy efficiency (EE) of the SC while guaranteeing the quality of service of each MU as well as small cell users (SUs). Specifically, given the minimum data rate requirement and the bandwidth provided by the MC, the SC jointly optimizes MU selection, bandwidth allocation, and power allocation while guaranteeing its own minimum required system data rate. The problem is challenging due to the binary MU selection variables and the fractional- form objective function. We first show that the bandwidth of an MU is shared with at most one SU in the SC. Then, for a given MU selection, the optimal bandwidth and power allocation is obtained by exploiting the fractional programming. To perform MU selection, we first introduce the concept of the trading EE to characterize the data rate obtained as well as the power consumed for serving an MU. We then reveal a sufficient and necessary condition for serving an MU without considering the total power constraint and the minimum data rate constraint: the trading EE of the MU should be higher than the system EE of the SC. Based on this insight, we propose a low complexity MU selection method and also investigate the optimality condition. Simulation results verify our theoretical findings and demonstrate that the proposed resource allocation achieves near-optimal performance.

[J 111] Distributed User-Centric Scheduling for Visible Light Communication Networks

L. Chen, J. Wang, J. Zhou, Derrick Wing Kwan Ng, R. Schober, and C. Zhao
Journal Paper Opt. Express 24(14), 15570-15589 (2016), Jul. 2016.

Abstract:

i

[J 112] Resource Allocation for a Massive MIMO Relay Aided Secure Communication

J. Chen, X. Chen, W. Gerstacker, and Derrick Wing Kwan Ng
Journal Paper IEEE Transactions on Information Forensics and Security, vol. 11, no. 8, pp. 1700-1711, Aug. 2016.

Abstract: In this paper, we address the problem of joint power and time allocation for secure communications in a decode-and-forward massive multiple-input multiple-output (M-MIMO) relaying system in the presence of a passive eavesdropper. We apply the M-MIMO relaying technique to enhance the secrecy performance under very practical and adverse conditions, i.e., no availability of instantaneous eavesdropper channel state information (CSI) and only imperfect instantaneous legitimate CSI. We first provide a performance analysis of secrecy outage capacity, which reveals the minimum required number of relay antennas for achieving a positive secrecy outage capacity. Then, we propose an optimization framework to jointly optimize source transmit power, relay transmit power, and transmission time in each hop, with the goal of maximizing the secrecy outage capacity. Although the secrecy outage capacity is not a concave function with respect to the optimization variables, we show that it can be maximized by first maximizing over some of the variables, and then maximizing over the rest. To this end, we first derive a closed-form solution of optimal relay transmit power, afterward obtain that of optimal source transmit power, and then derive the optimal ratio of the first-hop duration to a complete transmission time. Moreover, several important system design insights are provided through asymptotic performance analysis. Finally, simulation results validate the effectiveness of the proposed joint resource allocation scheme.

[J 113] Practical Non-linear Energy Harvesting Model and Resource Allocation for SWIPT Systems

E. Boshkovska, Derrick Wing Kwan Ng, N. Zlatanov, and R. Schober
Journal Paper IEEE Communications Letters, vol.19, no.12, pp.2082-2085, Dec. 2015.

Listed as one of the top most downloaded articles of the IEEE Communications Letters in Oct. 2015, Nov. 2015, Dec. 2015, Jan. 2016, Feb. 2016, Apr. 2016, and May 2016.

Abstract: In this letter, we propose a practical non-linear energy harvesting model and design a resource allocation algorithm for simultaneous wireless information and power transfer (SWIPT) systems. The algorithm design is formulated as a non-convex optimization problem for the maximization of the total harvested power at energy harvesting receivers subject to minimum required signal-to-interference-plus-noise ratios (SINRs) at multiple information receivers. We transform the considered non-convex objective function from sum-of-ratios form into an equivalent objective function in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. In each iteration, a rank-constrained semidefinite program (SDP) is solved optimally by SDP relaxation. Numerical results unveil a substantial performance gain that can be achieved if the resource allocation design is based on the proposed non-linear energy harvesting model instead of the traditional linear model.

image

A comparison between the harvested power for the proposed non-linear energy harvesting model in the letter and the measurement data from two different practical EH circuits with different dynamic ranges from [7] and [8] in the letter.

image

Average total harvested power (dBm) versus the minimum required SINR (dB). The baseline scheme is a resource allocation algorithm which is optimized for maximization of the total system harvested power according to the conventional linear energy harvesting model.

[J 114] Secrecy Wireless Information and Power Transfer: Challenges and Opportunities

X. Chen, Derrick Wing Kwan Ng, and H.-H. Chen
Journal Paper in IEEE Wireless Communications, vol. 23, no. 2, pp. 54-61, Apr. 2016.

Abstract: Wireless information and power transfer (WIPT) enables more sustainable and resilient communications owing to the fact that it avoids frequent battery charging and replacement. However, it also suffers from possible information interception due to the open nature of wireless channels. Compared to traditional secure communications, secrecy wireless information and power transfer (SWIPT) carries several distinct characteristics. On one hand, wireless power transfer may increase the vulnerability of eavesdropping, since a power receiver, as a potential eavesdropper, usually has a shorter access distance than an information receiver. On the other hand, wireless power transfer can be exploited to enhance wireless security. This article reviews the security issues in various SWIPT scenarios, with an emphasis on revealing the corresponding challenges and opportunities for implementing SWIPT. Furthermore, we provide a survey on a variety of physical layer security techniques to improve secrecy performance. In particular, we propose to use massive multiple-input multiple-output (MIMO) techniques to enhance power transfer efficiency and secure information transmission simultaneously. Finally, we discuss several potential research directions to further enhance the security in SWIPT systems.

[J 115] User-Centric Energy Efficiency Maximization for Wireless Powered Communications

Q. Wu, W. Chen, Derrick Wing Kwan Ng, and R. Schober
Journal Paper accepted for publication, IEEE Trans. Wireless Commun., Jul. 2016.

Abstract: In this paper, we consider wireless powered communication networks (WPCNs) where multiple users harvest energy from a dedicated power station and then communicate with an information receiving station in a time-division manner. Our goal is to maximize the weighted sum of the user energy efficiencies (WSUEE). In contrast to the existing system-centric approaches, the choice of the weights provides flexibility for balancing the individual user energy efficiencies (EEs) via joint time allocation and power control. We first investigate the WSUEE maximization problem without quality of service constraints. Closed-form expressions for the WSUEE as well as the optimal time allocation and power control are derived. Based on this result, we characterize the EE tradeoff between the users in the WPCN. Subsequently, we study the WSUEE maximization problem in a generalized WPCN where each user is equipped with an initial amount of energy and also has a minimum throughput requirement. By exploiting the sum-of-ratios structure of the objective function, we transform the resulting non-convex optimization problem into a two-layer subtractive-form optimization problem, which leads to an efficient approach for obtaining the optimal solution. Simulation results verify our theoretical findings and demonstrate the effectiveness of the proposed approach

[J 116] Multi-Objective Optimization for Robust Power Efficient and Secure Full-Duplex Wireless Communication Systems

Y. Sun, Derrick Wing Kwan Ng, V. Zhu, and R. Schober
Journal Paper accepted for publication, IEEE Trans. Wireless Commun., Apr. 2016.

Abstract: In this paper, we investigate the power efficient resource allocation algorithm design for secure multiuser wireless communication systems employing a full-duplex (FD) base station (BS) for serving multiple half-duplex (HD) downlink (DL) and uplink (UL) users simultaneously. We propose a multi-objective optimization framework to study two conflicting yet desirable design objectives, i.e., total DL transmit power minimization and total UL transmit power minimization. To this end, the weighed Tchebycheff method is adopted to formulate the resource allocation algorithm design as a multi-objective optimization problem (MOOP). The considered MOOP takes into account the quality-of-service (QoS) requirements of all legitimate users for guaranteeing secure DL and UL transmission in the presence of potential eavesdroppers. Thereby, secure UL transmission is enabled by the FD BS and would not be possible with an HD BS. The imperfectness of the channel state information of the eavesdropping channels and the inter-user interference channels is incorporated for robust resource allocation algorithm design. Although the considered MOOP is non-convex, we solve it optimally by semidefinite programming (SDP) relaxation. Simulation results not only unveil the trade-off between the total DL transmit power and the total UL transmit power, but also confirm the robustness of the proposed algorithm against potential eavesdroppers.

[J 117] Robust Layered Transmission in Secure MISO Multiuser Unicast Cognitive Radio Systems

Derrick Wing Kwan Ng, M. Shaqfeh, R. Schober, and H. Alnuweiri
Journal Paper accepted for publication, IEEE Trans. on Veh. Technol., Nov. 2015.

Abstract: This paper studies robust resource allocation algorithm design for a multiuser multiple-input single-output (MISO) cognitive radio (CR) downlink communication network. We focus on a secondary system which provides wireless unicast secure layered video information to multiple single-antenna secondary receivers. The resource allocation algorithm design is formulated as a non-convex optimization problem for the minimization of the total transmit power at the secondary transmitter. The proposed framework takes into account a quality of service (QoS) requirement regarding video communication secrecy in the secondary system, the imperfection of the channel state information (CSI) of potential eavesdroppers (primary receivers) at the secondary transmitter, and a limit for the maximum tolerable received interference power at the primary receivers. Thereby, the proposed problem formulation exploits the self-protecting architecture of layered transmission and artificial noise generation to ensure communication secrecy. {The considered non-convex optimization problem is recast as a convex optimization problem via semidefinite programming (SDP) relaxation. It is shown that the global optimal solution of the original problem can be constructed by exploiting both the primal and the dual optimal solutions of the SDP relaxed problem. Besides, two suboptimal resource allocation schemes are proposed for the case when the solution of the dual problem is unavailable for constructing the optimal solution.} Simulation results demonstrate significant transmit power savings and robustness against CSI imperfection for the proposed optimal and suboptimal resource allocation algorithms employing layered transmission compared to baseline schemes employing traditional single-layer transmission.

[J 118] Artificial Noise Assisted Secure Transmission for Distributed Antenna Systems

H.-M. Wang, C. Wang, and Derrick Wing Kwan Ng, M. H. Lee, and J. Xiao
Journal Paper accepted for publication, IEEE Trans. Signal Process., Apr. 2016.

Abstract:This paper studies the artificial noise (AN) assisted secure transmission for a distributed antenna systems (DAS). To avoid a significant overhead caused by full legitimate channel state information (CSI) acquisition, tracking and collection in the central processor, we propose a distributed AN scheme utilizing the large-scale CSI of the legitimate receiver and eavesdropper. Our objective is to maximize the ergodic secrecy rate (ESR) via optimizing the power allocation between the confidential signal and AN for each remote antenna (RA) under the per-antenna power constraint. Specifically, exploiting random matrix theory, we first establish an analytical expression of the achievable ESR, which leads to a non-convex optimization problem with multiple non-convex constraints in the form of high-order fixed-point equations. To handle the intractable constraints, we recast the problem into a max-min optimization problem, and propose an iterative block coordinate descent (BCD) algorithm to provide a local optimum solution of the problem. The BCD algorithm is composed of three subproblems, where the first two subproblems are convex with closed-form solutions, and the last one is a convex-concave game whose saddle-point is located by a tailored barrier algorithm. Simulation results validate the effectiveness of the proposed iterative algorithm and show that our scheme not only reduces the system overhead greatly but also maintains a good secrecy performance

[J 119] Energy-Efficient 5G Outdoor-to-Indoor Communication: SUDAS Over Licensed and Unlicensed Spectrum

Derrick Wing Kwan Ng, M. Breiling, C. Rohde, F. Burkhardt and R. Schober
Journal Paper accepted for publication, IEEE Trans. on Wireless Commun., Dec. 2015

Abstract: In this paper, we study the design of the user selection, the time allocation to uplink and downlink, and the transceiver processing matrix for uplink and downlink multicarrier transmission employing a shared user equipment (UE)-side distributed antenna system (SUDAS). The proposed SUDAS simultaneously utilizes licensed frequency bands and unlicensed frequency bands (e.g. millimeter wave bands) to enable a spatial multiplexing gain for single-antenna UEs to improve the energy efficiency and throughput of 5-th generation (5G) outdoor-to-indoor communication. The resource allocation algorithm design is formulated as a non-convex optimization problem for the maximization of the end-to-end system energy efficiency (bits/Joule). The non-convex matrix optimization problem is converted to an equivalent non-convex scalar optimization problem for multiple parallel channels, which is solved by an asymptotically globally optimal iterative algorithm. Besides, we propose a suboptimal algorithm which finds a locally optimal solution of the non-convex optimization problem. Simulation results illustrate that the proposed resource allocation algorithms for SUDAS achieve a significant performance gain in terms of system energy efficiency and spectral efficiency compared to conventional baseline systems by offering multiple parallel data streams for single-antenna UEs.

[J 120] Energy-Efficient Resource Allocation for Wireless Powered Communication Networks

Q. Wu, M. Tao, Derrick Wing Kwan Ng, W. Chen, and R. Schober
Journal Paper accepted, IEEE Trans. Wireless Commun., Nov. 2015.

Listed as one of the top most downloaded articles of the IEEE Trans. Wireless Commun. in Mar. 2016, Apr. 2016, May 2016, and Jun. 2016.

Abstract: This paper considers a wireless powered communication network (WPCN), where multiple users harvest energy from a dedicated power station and then communicate with an information receiving station. Our goal is to investigate the maximum achievable energy efficiency (EE) of the network via joint time allocation and power control while taking into account the initial battery energy of each user. We first study the EE maximization problem in the WPCN without any system throughput requirement. We show that the EE maximization problem for the WPCN can be cast into EE maximization problems for two simplified networks via exploiting its special structure. For each problem, we derive the optimal solution and provide the corresponding physical interpretation, despite the non-convexity of the problems. Subsequently, we study the EE maximization problem under a minimum system throughput constraint. Exploiting fractional programming theory, we transform the resulting non-convex problem into a standard convex optimization problem. This allows us to characterize the optimal solution structure of joint time allocation and power control and to derive an efficient iterative algorithm for obtaining the optimal solution. Simulation results verify our theoretical findings and demonstrate the effectiveness of the proposed joint time and power optimization.

[J 121] Power Efficient Resource Allocation for Full-Duplex Radio Distributed Antenna Networks

Derrick Wing Kwan Ng Y. Wu, and R. Schober
Journal Paper accepted for publication, IEEE Trans. on Wireless Comm., Dec. 2015.

Abstract

In this paper, we study the resource allocation algorithm design for distributed antenna multiuser networks with full-duplex (FD) radio base stations (BSs) which enable simultaneous uplink and downlink communications. The considered resource allocation algorithm design is formulated as an optimization problem taking into account the antenna circuit power consumption of the BSs and the quality of service (QoS) requirements of both uplink and downlink users. We minimize the total network power consumption by jointly optimizing the downlink beamformer, the uplink transmit power, and the antenna selection. To overcome the intractability of the resulting problem, we reformulate it as an optimization problem with decoupled binary selection variables and non-convex constraints. The reformulated problem facilitates the design of an iterative resource allocation algorithm which obtains an optimal solution based on the generalized Bender's decomposition (GBD) and serves as a benchmark scheme. Furthermore, to strike a balance between computational complexity and system performance, a suboptimal algorithm with polynomial time complexity is proposed. Simulation results illustrate that the proposed GBD based iterative algorithm converges to the global optimal solution and the suboptimal algorithm achieves a close-to-optimal performance. Our results also demonstrate the trade-off between power efficiency and the number of active transmit antennas when the circuit power consumption is taken into account. In particular, activating an exceedingly large number of antennas may not be a power efficient solution for reducing the total system power consumption. In addition, our results reveal that FD systems facilitate significant power savings compared to traditional half-duplex systems, despite the non-negligible self-interference.

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[J 122] Artificial Noise Assisted Secure Transmission under Training and Feedback

H.-M. Wang, C. Wang, and Derrick Wing Kwan Ng
Journal Paper IEEE Trans. Signal Process., vol.63, no.23, pp.6285-6298, Dec.1, 2015.

Abstract: This paper proposes a framework for the artificial noise assisted secure transmission in multiple-input, multiple-output, multiple antenna eavesdropper (MIMOME) wiretap channels in frequency-division duplexed (FDD) systems. We focus on a practical scenario that only the eavesdroppers' channel distribution information (CDI) is available and the imperfect channel state information (CSI) of the legitimate receiver is acquired through training and analog feedback. By taking explicitly into account the signaling overhead and training power overhead incurred by channel estimation and feedback, we define the achievable effective ergodic secrecy rate (ESR), and investigate a joint power allocation and training overhead optimization problem for the maximization of effective ESR. We first derive a deterministic approximation for the achievable effective ESR which facilitates the joint optimization. Then, efficient iterative algorithms are proposed to solve the considered nonconvex optimization problem. In particular, in the high-SNR regime, a block coordinate descent method (BCDM) is proposed to handle the joint optimization. In the low-SNR regime, we transform the problem into a sequence of geometric programmings (GPs) and locate its Karush-Kuhn-Tucker (KKT) solution using the successive convex approximation (SCA) method. For the general case of SNR, we maximize the lower bound of the achievable effective ESR. Simulation results corroborate the theoretical analysis and illustrate the secrecy performance of the proposed secure transmission scheme..

[J 123] Secure Massive MIMO Transmission with an Active Eavesdropper

Y. Wu, R. Schober, Derrick Wing Kwan Ng, C. Xiao, and G. Caire
Journal Paper IEEE Transactions on Information Theory, vol. 62, no. 7, pp. 3880-3900, July 2016.

Abstract: In this paper, we investigate secure and reliable transmission strategies for multi-cell multi-user massive multipleinput multiple-output (MIMO) systems with a multi-antenna active eavesdropper. We consider a time-division duplex system where uplink training is required and an active eavesdropper can attack the training phase to cause pilot contamination at the transmitter. This forces the precoder used in the subsequent downlink transmission phase to implicitly beamform towards the eavesdropper, thus increasing its received signal power. Assuming matched filter precoding and artificial noise (AN) generation at the transmitter, we derive an asymptotic achievable secrecy rate when the number of transmit antennas approaches infinity. For the case of a single-antenna active eavesdropper, we obtain a closed-form expression for the optimal power allocation policy for the transmit signal and the AN, and find the minimum transmit power required to ensure reliable secure communication. Furthermore, we show that the transmit antenna correlation diversity of the intended users and the eavesdropper can be exploited in order to improve the secrecy rate. In fact, under certain orthogonality conditions of the channel covariance matrices, the secrecy rate loss introduced by the eavesdropper can be completely mitigated.

[J 124] Multi-Objective Resource Allocation for Secure Communication in Cognitive Radio Networks with Wireless Information and Power Transfer

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper accepted for publication, IEEE Trans. on Veh. Technol., May 2015.

Listed as one of the top most downloaded articles of the IEEE Trans. on Veh. Technol. in Jun. 2015, Sep. 2015, Oct. 2015, Nov. 2015, Dec. 2015, Jan. 2016, Feb. 2016, Apr. 2016, May 2016, and Jun. 2016.

Abstract

In this paper, we study resource allocation for multiuser multiple-input single-output (MISO) secondary com- munication systems with multiple system design objectives. We consider cognitive radio (CR) networks where the secondary receivers are able to harvest energy from the radio frequency when they are idle. The secondary system provides simultaneous wireless power and secure information transfer to the secondary receivers. We propose a multi-objective optimization framework for the design of a Pareto optimal resource allocation algorithm based on the weighted Tchebycheff approach. In particular, the algorithm design incorporates three important system design objectives: total transmit power minimization, energy harvest- ing efficiency maximization, and interference power leakage-to- transmit power ratio minimization. The proposed framework takes into account a quality of service (QoS) requirement regarding communication secrecy in the secondary system and the imperfection of the channel state information (CSI) of potential eavesdroppers (idle secondary receivers and primary receivers) at the secondary transmitter. The proposed framework includes total harvested power maximization and interference power leakage minimization as special cases. The adopted multi- objective optimization problem is non-convex and is recast as a convex optimization problem via semidefinite programming (SDP) relaxation. It is shown that the global optimal solution of the original problem can be constructed by exploiting both the primal and the dual optimal solutions of the SDP relaxed problem. Besides, two suboptimal resource allocation schemes for the case when the solution of the dual problem is unavailable for constructing the optimal solution are proposed. Numerical results not only demonstrate the close-to-optimal performance of the proposed suboptimal schemes, but also unveil an inter- esting trade-off between the considered conflicting system design objectives

belterralizard1 belterralizard2

The left hand side is the considered CR communication system model for SWIPT. The right hand side depicts the three-dimensional system objective trade-off regions achieved by the proposed optimal resource allocation scheme. Asterisk markers denote the trade-off region achieved by the resource allocation scheme and colored circles represent the Pareto frontier.

[J 125] Secure and Green SWIPT in Distributed Antenna Networks with Limited Backhaul Capacity

Derrick Wing Kwan Ng and R. Schober
Journal Paper accepted for publicaiton, IEEE Trans. Wireless Commun., May 2015.

Listed as one of the top most downloaded articles of the IEEE Trans. Wireless Commun. in Sep. 2015 and Oct. 2015.

Abstract

This paper studies the resource allocation algorithm design for secure information and renewable green energy transfer to mobile receivers in distributed antenna communication systems. In particular, distributed remote radio heads (RRHs/antennas) are connected to a central processor (CP) via capacity-limited backhaul links to facilitate joint transmission. The RRHs and the CP are equipped with renewable energy harvesters and share their energies via a lossy micropower grid for improving the efficiency in conveying information and green energy to mobile receivers via radio frequency (RF) signals. The considered resource allocation algorithm design is formulated as a mixed non-convex and combinatorial optimization problem taking into account the limited backhaul capacity and the quality of service requirements for simultaneous wireless information and power transfer (SWIPT). We aim at minimizing the total network transmit power when only imperfect channel state information of the wireless energy harvesting receivers, which have to be powered by the wireless network, is available at the CP. In light of the intractability of the problem, we reformulate it as an optimization problem with binary selection, which facilitates the design of an iterative resource allocation algorithm to solve the problem optimally using the generalized Bender's decomposition (GBD). Furthermore, a suboptimal algorithm is proposed to strike a balance between computational complexity and system performance. Simulation results illustrate that the proposed GBD based algorithm obtains the global optimal solution and the suboptimal algorithm achieves a close-to-optimal performance. Besides, the distributed antenna network for SWIPT with renewable energy sharing is shown to require a lower transmit power compared to a traditional system with multiple co-located antennas.

belterralizard1 belterralizard2

The left hand side is a distributed antenna multiuser downlink communication system model with a central processor (CP), L=4 remote radio heads (RRHs), K=2 information receivers (IRs), and M=2 energy harvesting receivers (ERs). The blue solid ellipsoids represent the information signals included for the different IRs. The red dotted ellipsoids illustrate the dual functionality of artificial noise in providing security and facilitating efficient energy transfer to the ERs.

The right hand side is a simplified micro-power grid model with a point of common coupling connecting a central processor (CP) and L=4 remote radio heads (RRHs). The black solid and blue dashed lines indicate the power line and backhaul connections, respectively.

belterralizard2

Simulation model.

[J 126] Joint Beamforming and Power Allocation for Secrecy in Peer-to-Peer Relay Networks

C. Wang, H.-M. Wang, Derrick Wing Kwan Ng, X.-G. Xia, and C. Liu
Journal Paper accepted for publication, IEEE Trans. Wireless Commun., Jan. 2015.

Abstract: This paper investigates the physical-layer security of a multiuser peer-to-peer (MUP2P) relay network for amplify-and- forward (AF) protocol, where a secure user and other unclassified users coexist with a multi-antenna eavesdropper and the eavesdropper can wiretap the confidential information in both two cooperative phases. Our goal is to optimize the transmit power of the source and the beamforming weights of the relays jointly for secrecy rate maximization subject to the minimum signal-to-interference-noise-ratio (SINR) constraint at each user, and the individual and total power constraints. Mathematically, the optimization problem is non-linear and non-convex, which does not facilitate an efficient resource allocation algorithm design. As an alternative, a null space beamforming scheme is adopted at the relays for simplifying the joint optimization and eliminating the confidential information leakage in the second cooperative phase, where the relay beamforming vector lies in the null space of the equivalent channel of the relay to eavesdropper links. Although the null space beamforming scheme simplifies the design of resource allocation algorithm, the considered problem is still non-convex and obtaining the global optimum is very difficult, if not impossible. Employing a sequential parametric convex approximation (SPCA) method, we propose an iterative algorithm to obtain an efficient solution of the non-convex problem. Besides, the proposed joint design algorithm requires a feasible starting point, we also propose a low complexity feasible initial points searching algorithm. Simulations demonstrate the validity of the proposed strategy.

[J 127] Application of Smart Antenna Technologies in Simultaneous Wireless Information and Power Transfer

Z. Ding, C. Zhong, Derrick Wing Kwan Ng, M. Peng, H. A. Suraweera, R. Schober, and H. Vincent Poor
Journal PaperIEEE Communications Magazine, vol.53, pp. 86--93, Apr. 2015.

Listed as one of the top most downloaded articles of the IEEE Communications Magazine in Apr. 2015.

Abstract

Simultaneous wireless information and power transfer (SWIPT) is a promising solution to increase the lifetime of wireless nodes and hence alleviate the energy bottleneck of energy constrained wireless networks. As an alternative to conventional energy harvesting techniques, SWIPT relies on the use of radio frequency signals, and is expected to bring some fundamental changes to the design of wireless communication networks. This article focuses on the application of advanced smart antenna technologies, including multiple-input multiple-output and relaying techniques, to SWIPT. These smart antenna tech- nologies have the potential to significantly improve the energy efficiency and also the spectral efficiency of SWIPT. Different network topologies with single and multiple users are investigated, along with some promising solutions to achieve a favorable trade-off between system performance and complexity. A detailed discussion of future research challenges for the design of SWIPT systems is also provided.

image The trade-off region of the average total harvested energy (mJ/s) and the average system achievable rate (bit/s/Hz) for the different receivers. The carrier frequency is 915 MHz and the receiver is located 10 meters from the transmitter. The total transmit power, noise power, transceiver antenna gain, and RF-to-electrical energy conversion loss are set to 10 Watt, ??23 dBm, 10 dBi, and 3 dB, respectively. The multipath fading coefficients are modelled as independent and identically distributed Rician random variables with a Rician K -factor of 6 dB.

[J 128] Simultaneous Wireless Information and Power Transfer in Modern Communication Systems

I. Krikidis, S. Timotheou, S. Nikolaou, G. Zheng, Derrick Wing Kwan Ng and R. Schober
Journal Paper accepted for publication at the IEEE Communications Magazine, Aug. 2014.

Listed as one of the top most downloaded articles of the IEEE Communications Magazine in Dec. 2014.

Abstract

Energy harvesting for wireless communication networks is a new paradigm that allows terminals to recharge their batteries from external energy sources in the surrounding environment. A promising energy harvesting technology is wireless power transfer where terminals harvest energy from electromagnetic radiation. Thereby, the energy may be harvested opportunistically from ambient electromagnetic sources or from sources that intentionally transmit electromagnetic energy for energy harvesting purposes. A particularly interesting and challenging scenario arises when sources perform simultaneous wireless information and power transfer (SWIPT), as strong signals not only increase power transfer but also interference. This paper provides an overview of SWIPT systems with a particular focus on the hardware realization of rectenna circuits and practical techniques that achieve SWIPT in the domains of time, power, antennas, and space. The paper also discusses the benefits of a potential integration of SWIPT technologies in modern communication networks in the context of resource allocation and cooperative cognitive radio networks.

image The trade-off region of the average system capacity (b/s/Hz) and the average total harvested energy (mJ/s) for different numbers of transmit antennas N_T and receivers, K. The carrier frequency is 915 MHz, and the information receiver and energy harvesting receivers are located at 30 m and 10 m from the transmitter, respectively. The total transmit power, noise power, transceiv- er antenna gain, and RF-to-DC conversion loss are set to 10 W, ??3 dBm, 10 dBi, and 3 dB, respectively.

[J 129] Robust Beamforming for Secure Communication in Systems with Wireless Information and Power Transfer

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol. 13, pp. 4599-4615, Aug. 2014.

Listed as one of the top most downloaded articles of the IEEE Trans. Wireless Commun. in Aug. 2014, Sep. 2014, Oct. 2014, Nov. 2014, Dec. 2014, Apr. 2015, Jan. 2016 and May 2016.

Abstract

This paper considers a multiuser multiple-input single-output (MISO) downlink system with simultaneous wireless information and power transfer. In particular, we focus on secure communication in the presence of passive eavesdroppers and potential eavesdroppers (idle legitimate receivers). We study the design of a resource allocation algorithm minimizing the total transmit power for the case when the legitimate receivers are able to harvest energy from radio frequency signals. Our design advocates the dual use of both artificial noise and energy signals in providing secure communication and facilitating efficient wireless energy transfer. The algorithm design is formulated as a non-convex optimization problem. The problem formulation takes into account artificial noise and energy signal generation for protecting the transmitted information against both considered types of eavesdroppers when imperfect channel state information (CSI) of the potential eavesdroppers and no CSI of the passive eavesdroppers are available at the transmitter. Besides, the problem formulation also takes into account different quality of service (QoS) requirements: a minimum required signal-to-interference-plus-noise ratio (SINR) at the desired receiver; maximum tolerable SINRs at the potential eavesdroppers; a minimum required outage probability at the passive eavesdroppers; and minimum required heterogeneous amounts of power transferred to the idle legitimate receivers. In light of the intractability of the problem, we reformulate the considered problem by replacing a non-convex probabilistic constraint with a convex deterministic constraint. Then, a semi-definite programming (SDP) relaxation approach is adopted to obtain the optimal solution for the reformulated problem. Furthermore, we propose a suboptimal resource allocation scheme with low computational complexity for providing communication secrecy and facilitating efficient energy transfer. Simulation results demonstrate the close-to-optimal performance of the proposed schemes and significant transmit power savings by optimization of the artificial noise and energy signal generation. image

[J 130] Wireless Information and Power Transfer: Energy Efficiency Optimization in OFDMA Systems

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol. 12, pp. 6352 -6370, Dec. 2013.

Listed as one of the top most downloaded articles of the IEEE Trans. Wireless Commun. in Dec. 2013, Jan. 2014, Feb. 2014, Mar. 2014, Apr. 2014, May 2014, Jun 2014, Jul. 2014, Aug. 2014, Sep. 2014, Oct. 2014, Nov. 2014, Dec. 2014, Jan. 2015, Feb. 2015, Mar. 2015, Apr. 2015, May 2015, Jun. 2015, Jul. 2015, Sep. 2015, Oct. 2015, Nov. 2015, Dec. 2015, Jan. 2016, Feb. 2016, Mar. 2016, Apr. 2016, May 2016, and Jun. 2016.

Abstract

This paper considers orthogonal frequency division multiple access (OFDMA) systems with simultaneous wireless information and power transfer. We study the resource allocation algorithm design for maximization of the energy efficiency of data transmission (bits/Joule delivered to the receivers). In particular, we focus on power splitting hybrid receivers which are able to split the received signals into two power streams for concurrent information decoding and energy harvesting. Two scenarios are investigated considering different power splitting abilities of the receivers. In the first scenario, we assume receivers which can split the received power into a continuous set of power streams with arbitrary power splitting ratios. In the second scenario, we examine receivers which can split the received power only into a discrete set of power streams with fixed power splitting ratios. For both scenarios, we formulate the corresponding algorithm design as a non-convex optimization problem which takes into account the circuit power consumption, the minimum data rate requirements of delay constrained services, the minimum required system data rate, and the minimum amount of power that has to be delivered to the receivers. By exploiting fractional programming and dual decomposition, suboptimal iterative resource allocation algorithms are developed to solve the non-convex problems. Simulation results illustrate that the proposed iterative resource allocation algorithms approach the optimal solution within a small number of iterations and unveil the trade-off between energy efficiency, system capacity, and wireless power transfer: (1) wireless power transfer enhances the system energy efficiency by harvesting energy in the radio frequency, especially in the interference limited regime; (2) the presence of multiple receivers is beneficial for the system capacity, but not necessarily for the system energy efficiency.image

[J 131] Power Allocation for an Energy Harvesting Transmitter with Hybrid Energy Sources

I. Ahmed, A. Ikhlef, Derrick Wing Kwan Ng, and R. Schober,
Journal Paper IEEE Trans. Wireless Commun., vol. 12, pp. 6255 - 6267, Dec. 2013.

Abstract

In this work, we consider a point-to-point communication link where the transmitter has a hybrid supply of energy. Specifically, the hybrid energy is supplied by a constant energy source and an energy harvester, which harvests energy from its surrounding environment and stores it in a battery which suffers from energy leakage. Our goal is to minimize the power consumed by the constant energy source for transmission of a given amount of data in a given number of time intervals. Two scenarios are considered for packet arrival. In the first scenario, we assume that all data packets have arrived before transmission begins, whereas in the second scenario, we assume that data packets are arriving during the course of data transmission. For both scenarios, we propose an optimal offline transmit power allocation scheme which provides insight into how to efficiently consume the energy supplied by the constant energy source and the energy harvester. For offline power allocation, we assume that causal and non-causal information regarding the channel and the amount of harvested energy is available a priori. For optimal online power allocation, we adopt a stochastic dynamic programming (DP) approach for both considered scenarios. For online power allocation, only causal information regarding the channel and the amount of harvested energy is assumed available. Due to the inherent high complexity of DP, we propose suboptimal online algorithms which are appealing because of their low complexity. Simulation results reveal that the offline scheme performs best among all considered schemes and the suboptimal online scheme provides a good performance-complexity tradeoff.

[J 132] Energy-Efficient Resource Allocation in OFDMA Systems with Hybrid Energy Harvesting Base Station

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol 12, pp. 3412-3427, Jul. 2013.

Abstract

We study resource allocation algorithm design for energy-efficient communication in an orthogonal frequency division multiple access (OFDMA) downlink network with hybrid energy harvesting base station (BS). Specifically, an energy harvester and a constant energy source driven by a non-renewable resource are used for supplying the energy required for system operation. We first consider a deterministic offline system setting. In particular, assuming availability of non-causal knowledge about energy arrivals and channel gains, an offline resource allocation problem is formulated as a non-convex optimization problem over a finite horizon taking into account the circuit energy consumption, a finite energy storage capacity, and a minimum required data rate. We transform this non-convex optimization problem into a convex optimization problem by applying time-sharing and exploiting the properties of non-linear fractional programming which results in an efficient asymptotically optimal offline iterative resource allocation algorithm for a sufficiently large number of subcarriers. In each iteration, the transformed problem is solved by using Lagrange dual decomposition. The obtained resource allocation policy maximizes the weighted energy efficiency of data transmission (weighted bit/Joule delivered to the receiver). Subsequently, we focus on online algorithm design. A conventional stochastic dynamic programming approach is employed to obtain the optimal online resource allocation algorithm which entails a prohibitively high complexity. To strike a balance between system performance and computational complexity, we propose a low complexity suboptimal online iterative algorithm which is motivated by the offline algorithm. Simulation results illustrate that the proposed suboptimal online iterative resource allocation algorithm does not only converge in a small number of iterations, but also achieves a close-to-optimal system energy efficiency by utilizing only causal channel s- ate and energy arrival information. image

[J 133] Energy-Efficient Resource Allocation in Multi-Cell OFDMA Systems with Limited Backhaul Capacity

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol 11, pp. 3618 -3631, Oct. 2012.

Abstract

We study resource allocation for energy-efficient communication in multi-cell orthogonal frequency division multiple access (OFDMA) downlink networks with cooperative base stations (BSs). We formulate the resource allocation problem for joint BS zero-forcing beamforming (ZFBF) transmission as a non-convex optimization problem which takes into account the circuit power consumption, the limited backhaul capacity, and the minimum required data rate. We transform the considered problem in fractional form into an equivalent optimization problem in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. In each iteration, a low-complexity suboptimal semi-orthogonal user selection policy is computed. Besides, by using the concept of perturbation function, we show that in the considered systems under some general conditions, the duality gap with respect to the power optimization variables is zero despite the non-convexity of the primal problem. Thus, dual decomposition can be used in each iteration to derive an efficient closed-form power allocation solution for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations, and unveil the trade-off between energy efficiency, network capacity, and backhaul capacity: (1) In the low transmit power regime, an algorithm which achieves the maximum spectral efficiency may also achieve the maximum energy efficiency; (2) a high spectral efficiency does not necessarily result in a high energy efficiency; (3) spectral efficiency is always limited by the backhaul capacity; (4) energy efficiency increases with the backhaul capacity only until the maximum energy efficiency is achieved. image

[J 134] Energy-Efficient Resource Allocation in OFDMA Systems with Large Numbers of Base Station Antennas

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol 11, pp. 3292-3304, Sep. 2012.

Abstract

In this paper, resource allocation for energy-efficient communication in an orthogonal frequency division multiple access (OFDMA) downlink network with a large number of transmit antennas is studied. The considered problem is modeled as a non-convex optimization problem which takes into account the circuit power consumption, imperfect channel state information at the transmitter (CSIT), and different quality of service (QoS) requirements including a minimum required data rate and a maximum tolerable channel outage probability. The power allocation, data rate adaptation, antenna allocation, and subcarrier allocation policies are optimized for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). By exploiting the properties of fractional programming, the resulting non-convex optimization problem in fractional form is transformed into an equivalent optimization problem in subtractive form, which leads to an efficient iterative resource allocation algorithm. In each iteration, the objective function is lower bounded by a concave function which can be maximized by using dual decomposition. Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations and demonstrate the trade-off between energy efficiency and the number of transmit antennas.

[J 135] Energy-Efficient Resource Allocation for Secure OFDMA Systems

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. on Veh. Technol., vol. 61, pp.2572-2585, Jul. 2012.

Abstract

In this paper, resource allocation for energy-efficient secure communication in an orthogonal frequency-division multiple-access (OFDMA) downlink network is studied. The considered problem is modeled as a nonconvex optimization problem that takes into account the sum-rate-dependent circuit power consumption, multiple-antenna eavesdropper, artificial noise generation, and different quality-of-service (QoS) requirements, including a minimum required secrecy sum rate and a maximum tolerable secrecy outage probability. The power, secrecy data rate, and subcarrier allocation policies are optimized for maximization of the energy efficiency of secure data transmission (bit/joule securely delivered to the users). The considered nonconvex optimization problem is transformed into a convex optimization problem by exploiting the properties of fractional programming, which results in an efficient iterative resource allocation algorithm. In each iteration, the transformed problem is solved by using dual decomposition. Simulation results illustrate that the proposed iterative resource allocation algorithm not only converges in a small number of iterations but maximizes the system energy efficiency and guarantees a nonzero secrecy data rate for the desired users as well. In addition, the obtained results unveil a tradeoff between energy efficiency and secure communication.

[J 136] Dynamic Resource Allocation in MIMO-OFDMA System with Full-Duplex and Hybrid Relaying

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. Commun, vol. 60, pp. 1291-1304, May 2012.

Abstract

In this paper, we formulate a joint optimization problem for resource allocation and scheduling in full-duplex multiple-input multiple-output orthogonal frequency division multiple access (MIMO-OFDMA) relaying systems with amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols. Our problem formulation takes into account heterogeneous data rate requirements for delay sensitive and non-delay sensitive users. We also consider a theoretically optimal hybrid relaying scheme as a performance benchmark, which allows a dynamic selection between AF relaying and DF relaying protocols with full-duplex and half-duplex relays. We show that under some mild conditions the optimal transmitter precoding and receiver post-processing matrices jointly diagonalize the MIMO-OFDMA relay channels for all considered relaying protocols transforming the resource allocation and scheduling problem into a scalar optimization problem. Dual decomposition is employed to solve this optimization problem and a distributed iterative resource allocation and scheduling algorithm with closed-form power and subcarrier allocation is derived. Simulation results not only illustrate that the proposed distributed algorithm converges to the optimal solution in a small number of iterations, but also demonstrate the potential performance gains achievable with full-duplex relaying protocols. image

[J 137] Secure Resource Allocation and Scheduling for OFDMA Decode-and-Forward Relay Network

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol.10, pp.3528-3540, Oct. 2011.

Abstract

In this paper, we formulate an optimization problem for secure resource allocation and scheduling in orthogonal frequency division multiple access (OFDMA) half-duplex decode-and-forward (DF) relay assisted networks. Our problem formulation takes into account artificial noise generation to combat a passive multiple antenna eavesdropper and the effects of imperfect channel state information at the transmitter (CSIT) in slow fading. The optimization problem is solved by dual decomposition which results in a highly scalable distributed iterative resource allocation algorithm. The packet data rate, secrecy data rate, power, and subcarrier allocation policies are optimized to maximize the average secrecy outage capacity (bit/s/Hz securely and successfully delivered to the users via relays). Simulation results illustrate that our proposed distributed iterative algorithm converges to the optimal solution in a small number of iterations and guarantees a non-zero secrecy data rate for given target secrecy outage and channel outage probability requirements. image

[J 138] Resource Allocation and Scheduling in Multi-Cell OFDMA Decode-and-Forward Relaying Networks

Derrick Wing Kwan Ng and R. Schober
Journal Paper IEEE Trans. Wireless Commun., vol.10, pp.2246-2258, Jul. 2011.

Abstract

In this paper, we formulate resource allocation and scheduling for multi-cell orthogonal frequency division multiple access (OFDMA) systems with half-duplex decode-and-forward (DF) relaying as a joint optimization problem taking into account multi-cell interference and heterogeneous user data rate requirements. For efficient multi-cell interference mitigation, we incorporate a time slot allocation strategy into the problem formulation. We transform the resulting non-convex and combinatorial optimization problem into a standard convex problem by imposing an interference temperature constraint, which yields a lower bound for the original problem. Subsequently, the transformed optimization problem is solved by dual decomposition and a semi-distributed iterative resource allocation algorithm with closed-form power and subcarrier allocation policies is derived to maximize the average weighted system throughput (bit/s/Hz/base station). Simulation results illustrate that our proposed semi-distributed algorithm achieves practically the same performance as the centralized optimal solution of the original non-convex problem and provides a substantial performance gain compared to single-cell resource allocation and scheduling schemes. image

[J 139] Cross-Layer Scheduling for OFDMA Amplify-and-Forward Relay Networks

Derrick Wing Kwan Ng and R. Schober
Journal Paper IEEE Trans. on Veh. Technol., vol. 59, pp. 1443-1458, Mar. 2010.

Abstract

In this paper, we consider cross-layer scheduling for the downlink of amplify-and-forward (AF) relay-assisted orthogonal frequency-division multiple-access (OFDMA) networks. The proposed cross-layer design takes into account the effects of imperfect channel-state information (CSI) at the transmitter (CSIT) in slow fading. The rate, power, and subcarrier allocation policies are optimized to maximize the system goodput (in bits per second per hertz successfully received by the users). The optimization problem is solved by using dual decomposition, resulting in a highly scalable distributed iterative resource-allocation algorithm. We also investigate the asymptotic performance of the proposed scheduler with respect to (w.r.t.) the numbers of users and relays. We find that the number of relays should grow faster than the number of users to fully exploit the multiuser diversity (MUD) gain. On the other hand, diversity from multiple relays can be exploited to enhance system performance when the MUD gain is saturated due to noise amplification at the AF relays. Furthermore, we introduce a feedback-reduction scheme to reduce the computational burden and the required amount of CSI feedback from the users to the relays. Simulation results confirm the derived analytical results for the growth of the system goodput and illustrate that the proposed distributed cross-layer scheduler only requires a small number of iterations to achieve practically the same performance as the optimal centralized scheduler, even if the information exchanged between the base station (BS) and the relays in each iteration is quantized, and the proposed CSI feedback reduction scheme is employed.

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[J 140] Power Control and Performance Analysis of Outage-Limited Cellular Network with MUD-SIC and Macro-Diversity

Derrick Wing Kwan Ng and V. K. N. Lau
Journal Paper IEEE Trans. Commun., vol 58, pp. 2734-2740, Sep. 2010.

Abstract

In this paper, we analyze the uplink goodput (bits/sec/Hz successfully decoded) and per-user packet outage in a cellular network using multi-user detection with successive interference cancellation (MUD-SIC). We are interested to study the role of macro-diversity (MDiv) between multiple base stations on the MUD-SIC performance where the effect of potential error-propagation during the SIC processing is taken into account. While the jointly optimal power and decoding order in the MUD-SIC are NP hard problem, we derive a simple on/off power control and asymptotically optimal decoding order with respect to the transmit power. Based on the information theoretical framework, we derive the closed-form expressions on the total system goodput as well as the per-user packet outage probability.

[J 141] Asymptotic Tradeoff between Cross-Layer Goodput Gain and Outage Diversity in OFDMA Systems with Slow Fading and Delayed CSIT

V. Lau, W. K. Ng, and D. S. W. Hui
Journal Paper IEEE Trans. Wireless Commun., vol. 7, pp. 2732-2739, Jul. 2008.

Abstract

here are two important aspects of cross-layer gains in multiuser OFDMA systems with slow fading channels. They are the system goodput gain as well as the packet diversity gain. The former aspect of cross-layer designs has been well- studied under perfect CSIT conditions and is known as the multi-user diversity gain (MuDiv). In cross-layer OFDMA systems with perfect CSIT, it is well known that the system throughput (ergodic capacity) scales in the order of O(log log K) due to the MuDiv gain, where K is the number users. However, in slow fading channels with delayed CSIT, there will always be potential packet errors (due to channel outage if the scheduled data rate exceeds the instantaneous mutual information) even if very strong channel coding is applied at the base station. In this case, the cross-layer packet outage diversity is important to protect the packet errors due to channel outage and there is a natural tradeoff between the goodput gain and packet diversity. In this paper, we shall focus on the asymptotic tradeoff analysis between the system goodput gain and the packet outage diversity gain in cross-layer OFDMA systems with delayed CSIT.

[J 142] Per-User Packet Outage Analysis in Slow Multi-Access Fading Channels with Successive Interference Cancellation for Equal Rate Applications

V. Lau and W. K. Ng
Journal Paper IEEE Trans. Wireless Commun., vol. 7, pp. 1754-1763, May 2008.

Abstract

In this paper, we derive analytically the per-user packet outage probability and the total system goodput for multiaccess systems using multiuser detector with adaptive successive interference cancellation (MUD-SIC). We consider a multiuser wireless system with n mobile users and a base station. We assume slow fading channels where packet transmission error (outage) is the primary concern even if strong channel coding is applied. To capture the effect of potential packet error, we consider the average packet error probability and the total system goodput, which measures the average b/s/Hz successfully delivered to the base station, of the n users. Unlike previous works, our analysis focus on the error-propagation effects in MUD-SIC detector where the packet outage event for the i-th decoded user is coupled with that in the i - 1,.., 1-th decoding attempts. We shall derive the optimal SIC decoding order (to maximize system goodput) and evaluate the closed-form per-user packet outage probabilities for the n users for MUD-SIC. Simulation results are used to verify the analytical expressions.

[Book 1] Wireless Information and Power Transfer: Theory and Practice

Derrick Wing Kwan Ng, Trung Q. Duong, Caijun Zhong, and Robert Schober
Book Wiley-IEEE Press, ISBN: 978-1-119-47679-5
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Book Description

The development of wireless communication networks worldwide has triggered a massive growth in the number of wireless communication devices and sensors for applications such as logistics and transportation, environmental monitoring, energy management, and safety management, etc. It is expected that in the era of the Internet of Things (IoT) in 2020, there will be 50 billion wireless communication devices connected together worldwide with a connection density of 1 million devices per km2. However, battery-powered wireless communication devices have limited energy storage capacity and their frequent replacement can be costly, cumbersome, or even impossible, which creates a serious performance bottleneck in realizing reliable and ubiquitous wireless communication networks. Wireless power transfer (WPT), offers a viable solution to facilitate efficient and sustainable communication networks to serve energy-limited communication devices. In this book, the authors discuss the circuit design, resource allocation algorithm design, and protocol design to tackle the above challenges by both theoretical and practical approaches which will bridge the gap between theory and practice, with long-term contributions to the evolution of future sustainable WIPT networks.







[Book 2] Key Technologies for 5G Wireless Systems

Vincent W. S. Wong, Robert Schober, Derrick Wing Kwan Ng, and Li-Chun Wang
Book Cambridge University Press, ISBN-10: 1107172411 (English version); ISBN: 9787115492777 (Simplified Chinese version)
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There are English version and Simplified Chinese version.

Book Description

Get up to speed with the state-of-the-art protocols, network architectures and techniques being considered for 5G wireless networks with this comprehensive and authoritative guide. It is an essential resource for researchers, practicing engineers and graduate students working in wireless communications and networking.







[B 1] Beamforming Design for Secure SWIPT Systems Under a Non-linear Energy Harvesting Model

E. Boshkovska. N. Zlatanov, X. Chen, Derrick Wing Kwan Ng, and R. Schober
Book ChapterEnergy Harvesting for Wireless Sensor Networks: Technology, Components and System Design (2018). Austria: De Gruyter.











[B 2] Energy-Efficient Radio Resource Management

Z. Wei, Y. Cai, Derrick Wing Kwan Ng, and J. Yuan in "Wiley 5G Ref: The Essential 5G Reference Online"
Book ChapterWiley,











[B 3] Resource Allocation for Wireless CommunicationNetworks with RF Energy Harvesting

E. Boshkovska, Derrick Wing Kwan Ng, and R. Schober in "From Internet of Things to Smart Cities: Enabling Technologies", Eds. by H.Sun, B. I. Ahmad, and C. Wang.
Book ChapterChapman and Hall/CRC , ISBN 9781498773782
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Resource Allocation for Wireless Communication Networks with RF Energy Harvesting











[B 4] Asymptotically Optimal Power Allocation for Wireless Powered Communication Network with Non-orthogonal Multiple Access

Nikola Zlatanov, Zoran Hadzi-Velkov, and Derrick Wing Kwan Ng, in "Wireless Power Transfer Algorithms, Technologies and Applications in Ad Hoc Communication Networks", Eds. by Nikoletseas, Sotiris, Yang, Yuanyuan, Georgiadis, Apostolos.
Book Chapter Springer International Publishing, ISBN 978-3-319-46809-9
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Asymptotically Optimal Power Allocation for Wireless Powered Communication Network with Non-orthogonal Multiple Access

In this chapter, we investigate a wireless powered communication network (WPCN) comprised of a power beacon that broadcasts radio frequency (RF) energy to a set of energy harvesting (EH) transmitters equipped with unlimited batteries, which use the harvested energy to transmit information back to the power-beacon in a non-orthogonal multiple access fashion. For this network, we propose a scheme which achieves the capacity region. Moreover, we show that the capacity region of the considered WPCN converges to the capacity region of its non-EH multiple access network, where the non-EH transmitters have specific average power constraints.




Keywords: Wireless powered communication network energy harvesting non-orthogonal multiple access

[B 5] SUDAS: mmWave Relaying for 5G Outdoor-to-Indoor Communications

M. Breiling, Derrick Wing Kwan Ng, C. Rohde, F. Burkhardt, and R. Schober, in "Advanced Relay Technologies in Next Generation Wireless Communications", Eds. by I. Krikidis and G. Zheng.
Book Chapter IET ISBN: 9781785610035,
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SUDAS: mmWave relaying for 5G outdoor-to-indoor communications

Background: The ambitious data rate target of 10 Gbit/s for the 5G standard is elusive despite the use of advanced air interface technologies such as massive MIMO, small cells, and mmWave communication links. In order to achieve this high target data rate for UEs inside a building, we propose in this section for 5G to employ an infrastructure of many low-price relay nodes installed in fixed indoor locations. These nodes relay signals received from the BS in a mobile UHF band via non-overlapping mmWave links to the UE, and vice versa. We refer to this scattered infrastructure as a Shared UE-side Distributed Antenna System (SUDAS). The proposed relaying scheme is limited to only two hops, namely between the BS and the relay nodes, and between the relay nodes and the UE. This simplification allows a low end-to-end latency and it avoids the significant overhead needed for exchanging routing information. In particular, each relay is called a Shared UE-side Distributed Antenna Component (SUDAC) in the proposed SUDAS. In practice, such SUDACs could be integrated into many devices with continuous power supply, including electrical outlets, lamps, and light outlets or other devices that carry Machine-Type-Communication (MTC) circuits in the future, such as TV sets and fridges. Besides, the SUDACs are dedicated low-cost devices and scattered in a room.

[B 6] Multiple-Antenna and Beamforming Systems with Simultaneous Wireless Information and Power Transfer

Derrick Wing Kwan Ng, S. Leng, and R. Schober, in "Wireless-Powered Communication Networks: Architectures, Protocols, and Applications".
Book Chapter Cambridge University Press ISBN: 9781107135697
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Multiple-Antenna and Beamforming Systems with Simultaneous Wireless Information and Power Transfer

Background: In 1899, Nikola Tesla proposed the wireless transmission of electrical power via a magnifying transmitter, an advanced version of the Tesla coil transmitter. The use of wireless power transfer (WPT) avoids the potentially high costs of planning, installing, displacing, and maintaining power cables in buildings and infrastructure. Despite its convenience, one of the major challenges in realizing WPT is its low power transfer efficiency. In practice, wireless power has to be transferred via a carrier signal with a high carrier frequency such that antennas of reasonable size can be used for harvesting power. The associated path loss severely attenuates the signal, leading to only a small amount of power being harvested at the receiver. Besides, the initial efforts on WPT focused on high-power-consumption applications. This raised serious public health concerns about strong electromagnetic radiation which prevented the further development of WPT in the late twentieth century. As a result, this area developed slowly until recent advances in silicon technology and multiple-antenna technology made WPT attractive once again. In particular, the breakthrough in silicon technology has significantly reduced the energy demand of simple wireless devices. Thus, harvesting energy1 from background radiofrequency (RF) signals originating from ambient transmitters can support the power needs of low-power-consumption receivers. Besides, multiple-antenna technology has revolutionized the design of traditional communication systems for a better utilization of limited system resources. For example, a multiple-antenna transmitter can focus its transmitted signal into certain locations to improve the signal reception at the receivers. It has been shown that the use of multiple antennas in communication systems can significantly reduce the total transmit power and improve the system energy efficiency for given QoS requirements. Thus, it is envisioned that multiple-antenna technology is also the key to unlock the potential of WPT.

[B 6] Cross-Layer Scheduling Design for Cooperative Wireless Two-Way Relay Networks

Derrick Wing Kwan Ng and R. Schober, in "Cooperative Cellular Wireless Networks", Cambridge University Press, Apr. 2011.
Book Chapter Cambridge University Press| April, 2011 | ISBN: 9780521767125
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Cooperative Cellular Wireless Networks, Eds. E. Hossain, D. I. Kim, and V. K. Bhargava

Background: The degrees of freedom introduced by multiple antennas at the transmitters and receivers of wireless communication systems facilitate multiplexing gains and diversity gains. A wireless point-to-point link with M transmit and N receive antennas constitutes an M-by-N multiple-input multiple-output (MIMO) communication system. The ergodic capacity of an M-by-N MIMO fading channel increases almost linearly with min{M,N} provided that the fading meets certain mild conditions. Hence, it is not surprising that MIMO has attracted a lot of research interest since it enables significant performance and throughput gains without requiring extra transmit power and bandwidth. However, limitations on the number of antennas that a wireless device is able to support as well as the significant signal processing power and complexity required in MIMO tranceivers limit the gains that can be achieved in practice. To overcome the limitations of traditional MIMO, the concept of cooperative communication has been proposed for wireless networks such as fixed infrastructure cellular networks and wireless ad-hoc networks. The basic idea of cooperative communication is that the single-antenna terminals of a multiuser system can share their antennas and create a virtual MIMO communication system. Thereby, three different types of cooperation may be distinguished, namely, user cooperation, base station (BS) cooperation, and relaying. Theoretically, user cooperation and BS cooperation are able to provide huge performance gains, when compared with noncooperative networks. However, the required information exchange between users and BSs may make these options less attractive in practice.

[C 1] Deep Transfer Learning-Assisted Signal Detection for Ambient Backscatter Communications

C. Liu, X. Liu, Z. Wei, Derrick Wing Kwan Ng, J. Yuan, and Y. C. Liang,
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 2] Sum-Rate Maximization for IRS- Assisted UAV OFDMA Communication Systems

Z. Wei, Y. Cai, Z. Sun, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 3] Joint Analog Beamforming and Jamming Optimization for Covert Millimeter Wave Communication

C. Wang, Z. Li, and Derrick Wing Kwan Ng
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 4] Physical Layer Secrecy and Transmission Resiliency of Device-to-Device Communications

M. Letafati, A. Kuhestani, and Derrick Wing Kwan Ng, and M. R. A. Beshkani,
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 5] Parametric Message-passing for Joint Localization and Synchronization in Cooperative Networks

W. Yuan, J. Yuan, and Derrick Wing Kwan Ng
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 6] Sum-Rate Maximization for Multiuser MISO Downlink Systems with Self-sustainable IRS

S. Hu, Z. Wei, Y. Cai, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 7] Power-Efficient Resource Allocation for Multiuser MISO Systems via Intelligent Reflecting Surfaces

X. Yu, D. Xu, Derrick Wing Kwan Ng, and R. Schober
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 8] Energy Efficiency and Spectral Efficiency Tradeoff in RIS-Aided Multiuser MIMO Uplink Systems

J. Xiong, L. You, Derrick Wing Kwan Ng, C. Yuan, W. Wang, and X. Gao
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 9] Covariance-Based Cooperative Activity Detection for Massive Grant-Free Random Acces

X. Shao, X. Chen, Derrick Wing Kwan Ng, C. Zhong, and Z. Zhang
Conference Papers IEEE Globecom, Dec. 2020.

Abstract:

[C 10] Joint Radar-Communication-Based Bayesian Predictive Beamforming for Vehicular Networks,

W. Yuan, F. Liu, C. Masouros, J. Yuan, and Derrick Wing Kwan Ng
Conference Papers invited paper, 2020 IEEE Radar Conference.

Abstract:

[C 11] Physical Layer Security of Vehicular Networks: A Stochastic Geometry Approach

C. Wang, Z. Li, J. Shi, J. Si, and Derrick Wing Kwan Ng
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 12] A New Frequency Hopping-Aided Secure Communication in the Presence of an Adversary Jammer and an Untrusted Relay

M. Letafati, A. Kuhestani, Derrick Wing Kwan Ng, and H. Behroozi
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 13] Robust Secure Resource Allocation for Downlink Two-user MISO Rate-Splitting Systems

H. Fu, S. Feng, W. Tang, and Derrick Wing Kwan Ng
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 14] Resource Allocation for Power-Efficient IRS-Assisted UAV Communications

Y. Cai, Z. Wei, S. Hu, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 15] Robust Chance- Constrained Trajectory and Transmit Power Optimization for UAV-Enabled CR Networks

Y. Zhou, H. Zhou, F. Zhou, Derrick Wing Kwan Ng, and R. Q. Hu,
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 16] Performance Trade-off Between Uplink and Downlink in Full-Duplex Communications

A. Khalili, M. Mili, and Derrick Wing Kwan Ng
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 17] NOMA-Based Cell-Free Massive MIMO Over Spatially Correlated Rician Fading Channels

J. Zhang, J. Fan, B. Ai, and Derrick Wing Kwan Ng
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 18] Joint Data and Active User Detection for Grant-free FTN-NOMA in Dynamic Networks

W. Yuan, N. Wu, J. Yuan Derrick Wing Kwan Ng, and L. Hanzo
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 19] Reconfigurable Intelligent Surfaces Assisted MIMO-MAC with Partial CSI

J. Xiong, L. You, Y. Huang, Derrick Wing Kwan Ng, W. Wang, and X. Gao
Conference Papers IEEE ICC, Jun. 2020.

Abstract:

[C 20] Energy and Spectral Efficiency Tradeoff in OFDMA Networks via Antenna Selection Strategy

A. Khalili and Derrick Wing Kwan Ng
Conference Papers IEEE WCNC, Apr. 2020

Abstract:

[C 21] Resource Allocation for Secure IRS-assisted Multiuser MISO System

D. Xu, X. Yu, Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers IEEE Globecom, Dec. 2019.

Abstract:

[C 22] Optimal Design of Wireless-Powered Hierarchical Fog-Cloud Computing Networks

J. Liu, K. Xiong, Derrick Wing Kwan Ng, P. Fan, and Z. Zhong
Conference Papers IEEE Globecom, Dec. 2019.

Abstract:

[C 23] Robust Beamforming Design for SWIPT in Cellular Internet of Things

Q. Qi, X. Chen, Derrick Wing Kwan Ng, C. Zhong, and Z. Zhang
Conference Papers ICCC, Jul. 2019

Abstract:

[C 24] A Two-Stage Beam Alignment Framework for Hybrid MmWave Distributed Antenna Systems

Z. Wei, M. Qiu, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers IEEE SPAWC 2019, Jul., 2019

Abstract:

[C 25] Robust Trajectory and Resource Allocation Design for Secure UAV-aided Communications

X. Sun, C. Shen, Derrick Wing Kwan Ng, and Z. Zhong
Conference Papers ICC, 2019, Shanghai, China

Abstract: This paper aims to enhance the physical layer security against potential internal eavesdroppings by exploiting the maneuverability of an unmanned aerial vehicle (UAV). We consider a scenario where two receivers with different security clearance levels require to be served by a legitimate transmitter with the aid of the UAV. We jointly design the trajectory and resource allocation to maximize the accumulated system confidential data rate. The design is formulated as a mixed-integer nonconvex optimization problem which takes into account the partial position information of a potential eavesdropper. To circumvent the problem non-convexity, a series of transformations and approximations are proposed which facilitates the design of a computationally efficient suboptimal solution. Simulation results are presented to provide important system design insights and demonstrate the advantages brought by the robust joint design for enhancing the physical layer security.

[C 26] Design of Beamspace Massive Access for Cellular Internet-of-Things

R. Jia, X. Chen, Derrick Wing Kwan Ng, and H. Lin, and Z. Zhang,
Conference Papers ICC, 2019, Shanghai, China

Abstract:

[C 27] Beamwidth Control for NOMA in Hybrid mmWave Communication Systems

Z. Wei, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers ICC, 2019, Shanghai, China

Abstract:

[C 28] A Distributed Multi-RF Chain Hybrid mmWave Scheme for Small-cell Systems

L. Zhao, J. Guo, Z. Wei, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers ICC, 2019, Shanghai, China

Abstract:

[C 29] Optimal Online Transmission Policy for Energy-Constrained Wireless-Powered Communication Networks

X. Li, X. Zhou, Derrick Wing Kwan Ng, and C. Sun
Conference Papers ICC, 2019, Shanghai, China

Abstract:

[C 30] Energy-Efficient Resource Allocation for Secure UAV Communication Systems

Y. Cai, Z. Wei, R. Li, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers WCNC, 2019, Marrakech, Morocco

Abstract:

[C 31] Joint Millimeter Wave and Microwave Wave Resource Allocation Design for Dual-Mode Base Stations

B. Fang, Z. Liao, Y. Wu, J. Jin, Derrick Wing Kwan Ng, X-G. Xi, and X. Gong
Conference Papers WCNC, 2019, Marrakech, Morocco

Abstract:

[C 32] Robust Resource Allocation for UAV Systems with UAV Jittering and User Location Uncertainty

D. Xu, Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers Globecom, 2018, Abu Dhabi, UAE

Abstract:

[C 33] Joint Trajectory and Resource Allocation Design for UAV Communication Systems

R. Li, Z. Wei, L. Yang, Derrick Wing Kwan Ng, N. Yang, J. Yuan, and J. An
Conference Papers Globecom, 2018, Abu Dhabi, UAE

Abstract:

[C 34] On the Performance Gain of NOMA over OMA in Uplink Single-cell System

Z. Wei, L. Yang, Derrick Wing Kwan Ng and J. Yuan
Conference Papers Globecom, 2018, Abu Dhabi, UAE

Abstract:

[C 35] Massive Access in the Presence of Imperfect Successive Interference Cancellation

X. Chen, R. Jia, C. Zhong, Derrick Wing Kwan Ng and Z. Zhang
Conference Papers International Conference on Wireless Communications and Signal Processing, Oct. 2018

Abstract:

[C 36] Optimal Beamforming for Multiuser Secure SWIPT Systems

Y. Su and Derrick Wing Kwan Ng
Conference Papers INISCOM 2018, Aug., Vietnam

image Received the Best Paper Award .

Abstract: In this paper, we study the beamforming design for simultaneous wireless information and power transfer (SWIPT) downlink systems. The design is formulated as a non-convex optimization problem which takes into account the quality of service (QoS) requirements of communication security and minimum harvested power. In particular, the proposed design advocates the dual use of energy signal to enable secure communication and efficient WPT. The globally optimal solution of the optimization problem is obtained via the semidefinite programming relaxation (SDR). Our simulation results show that there exists a non-trivial tradeoff between the achievable data rate and the total harvested power in the system. Besides, our proposed optimal scheme provides a substantial performance gain compared to a simple suboptimal scheme based on the maximum ratio transmission (MRT).

[C 37] Resource Allocation for Solar Powered UAV Communication Systems

Y. Sun, Derrick Wing Kwan Ng, D. Xu, L. Dai, and R. Schober
Conference Papers IEEE SPAWC 2018

Abstract:

[C 38] A Multi-Beam NOMA Framework for Hybrid mmWave Systems

Z. Wei, L. Zhao, J. Guo, Derrick Wing Kwan Ng, G. Xiaohu, Z. Ding, V. W.S. Wong, and R. Schober
Conference Papers ICC, 2018, Kansas city, USA.

image Received the Best Paper Award .

Abstract:

[C 39] Cache-Aided Non-Orthogonal Multiple Access

L. Xiang, Derrick Wing Kwan Ng, G. Xiaohu, Z. Ding, V. W.S. Wong, and R. Schober
Conference Papers ICC, 2018, Kansas city, USA.

Abstract:

[C 40] Mitigating Pilot Contamination in Multi-cell Hybrid Millimeter Wave Systems

L. Zhao, Z. Wei, Derrick Wing Kwan Ng, J. Yuan, and M. C. Reed
Conference Papers ICC, 2018, Kansas city, USA.

Abstract:

[C 41] On the Capacity of SWIPT Systems with a Nonlinear Energy Harvesting Circuit

R. Morsi, V. Jamali, Derrick Wing Kwan Ng, R. Schober
Conference Papers ICC, 2018, Kansas city, USA.

Abstract:

[C 42] Joint Estimation of Channel Parameters in Massive MIMO Systems via PARAFAC Analysis

X. Wei, W. Peng, Derrick Wing Kwan Ng, R. Schober, and T. Jiang
Conference Papers accepted for publication, ICNC 2018, Maui, Hawaii.

Abstract:

[C 43] Resource Allocation for MC-NOMA Systems with Cognitive Relaying

Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers accepted for publication, Globecom 2017, Singapore.

Abstract: In this paper, we investigate the resource allocation algorithm design for cooperative cognitive relaying multicarrier non-orthogonal multiple access (MC-NOMA) systems. In particular, the secondary base station serves multiple secondary users and simultaneously acts as a relay assisting the information transmission in the primary network. The resource allocation aims to maximize the weighted system throughput by jointly optimizing the power and subcarrier allocation for both the primary and the secondary networks while satisfying the quality-of-service requirements of the primary users. The algorithm design is formulated as a mixed combinatorial non-convex optimization problem. We apply monotonic optimization theory to solve the problem leading to an optimal resource allocation policy. Besides, we develop a low-complexity scheme to find a suboptimal solution. Our simulation results reveal that the performance of the proposed suboptimal algorithm closely approaches that of the optimal one. Besides, the combination of MC-NOMA and cognitive relaying improves the system throughput considerably compared to conventional multicarrier cognitive relaying systems.

[C 44] Secure Video Streaming in Heterogeneous Small Cell Networks with Untrusted Cache Helpers

L. Xiang, Derrick Wing Kwan Ng, V. W.S. Wong, and R. Schober
Conference Papers accepted for publication, Globecom 2017, Singapore.

Abstract: This paper studies secure video streaming in cacheenabled small cell networks, where some of the cache-enabled small cell base stations (BSs) helping in video delivery are untrusted. Unfavorably, caching improves the eavesdropping capability of these untrusted helpers as they may intercept both the cached and the delivered video files. To address this issue, we propose joint caching and scalable video coding (SVC) of video files to enable secure cooperative multiple-input multiple-output (MIMO) transmission and exploit the cache memory of all BSs for improving system performance. The caching and delivery design is formulated as a non-convex mixed-integer optimization problem to minimize the total BS transmit power required for secure video streaming. We develop an algorithm based on the modified generalized Benders decomposition (GBD) to solve the problem optimally. Inspired by the optimal algorithm, a low-complexity suboptimal algorithm is also proposed. Simulation results show that the proposed schemes achieve significant gains in power efficiency and secrecy performance compared to three baseline schemes.

[C 45] Power-Efficient Multi-Quality Multicast Beamforming based on SVC and Superposition Coding,

C. Guo, Y. Cui, Derrick Wing Kwan Ng,and Z. Liu
Conference Papers accepted for publication, Globecom 2017, Singapore.

Abstract:

[C 46] C-RAN with Hybrid RF/FSO Fronthaul Links: Joint Optimization of RF Time and Fronthaul Compression

M. Najafi, V. Jamali, Derrick Wing Kwan Ng, and R. Schober
Conference Papers accepted for publication, Globecom 2017, Singapore.

Abstract: This paper considers the uplink of a cloud radio access network (C-RAN) comprised of several multi-antenna remote radio units (RUs) which send the data that they received from multiple mobile users (MUs) to a central unit (CU) via a wireless fronthaul link. One of the fundamental challenges in implementing C-RAN is the huge data rate required for fronthauling. To address this issue, we employ hybrid radio frequency (RF)/free space optical (FSO) systems for the fronthaul links as they benefit from both the large data rates of FSO links and the reliability of RF links. To efficiently exploit the fronthaul capacity, the RUs employ vector quantization to jointly compress the signals received at their antennas. Moreover, due to the limited available RF spectrum, we assume that the RF multiple-access and fronthaul links employ the same RF resources. Thereby, we propose an adaptive protocol which allocates transmission time to the RF multiple-access and fronthaul links in a time division duplex (TDD) manner and optimizes the quantization noise covariance matrix at each RU such that the sum rate is maximized. Our simulation results reveal that a considerable gain in terms of sum rate can be achieved by the proposed protocol in comparison with benchmark schemes from the literature, especially when the FSO links experience unfavorable atmospheric conditions.

[C 47] Spectrum-Power Trading for Energy-Efficient Device-Centric Overlaying Communications,

Q. Wu, F. Wang, Derrick Wing Kwan Ng, and W. Chen
Conference Papers accepted for publication, Globecom 2017, Singapore.

Abstract: In this paper, we propose device-to-device (D2D) overlaying communications with spectrum-power trading where D2D users (DUs) consume transmit power to relay the data of cell-edge cellular users (CUs) for uplink transmission in exchange for bandwidth from CUs for D2D communications. The proposed spectrum-power trading aims at exploiting individual disparities from both the spectrum and the power perspectives. Our goal is to maximize the weighted sum EE (WSEE) of DUs via a joint D2D relay selection, bandwidth allocation, and power allocation while guaranteeing the quality of service of each CU. We show that for a given D2D relay selection, the objective function of the WSEE maximization problem in a fractional form can be transformed into a subtractive-form that is more tractable based on the fractional programming theory. To perform D2D relay selection, we first reveal an important property, which connects the WSEE with both the system-centric EE and the fairness-centric EE. Based on this insight, the D2D relay selection problem is cast into a minimum weighted bipartite matching problem that can be solved efficiently with optimality. Simulation results demonstrate the effectiveness of the proposed scheme and algorithm.

[C 48] Power-efficient and Secure WPCNs with Residual Hardware Impairments and a Non-linear EH Model,

E. Boshkovska, Derrick Wing Kwan Ng, and R. Schober
Conference Papers accepted for publication, Globecom 2017, Singapore.

Abstract: In this paper, we design a resource allocation algorithm for a wireless-powered communication network (WPCN) taking into account residual hardware impairments (HWIs) at the transceivers and the non-linearity of radio frequency (RF) energy harvesting (EH) circuits. In order to ensure communication secrecy, physical layer (PHY) security techniques are exploited to deliberately degrade the channel quality of a multipleantenna eavesdropper. The resource allocation algorithm design is formulated as a non-convex optimization problem for the minimization of the total consumed power in the network, while guaranteeing the quality of service (QoS) of the information receivers (IRs). The globally optimal solution of the optimization problem is obtained via a one-dimensional search and semidefinite programming (SDP) relaxation. Numerical results demonstrate that the proposed scheme can significantly reduce the power consumption of the system compared to a baseline scheme, which assumes ideal hardware.

[C 49] Max-min Fair Beamforming for SWIPT Systems with Non-linear EH Model

E. Boshkovska, X. Chen, L. Dai, Derrick Wing Kwan Ng, and R. Schober
Conference Papers accepted for publication, VTC 2017, Fall.

Abstract: We study the beamforming design for multiuser systems with simultaneous wireless information and power trans- fer (SWIPT). Employing a practical non-linear energy har- vesting (EH) model, the design is formulated as a non-convex optimization problem for the maximization of the minimum harvested power across several energy harvesting receivers. The proposed problem formulation takes into account imperfect channel state information (CSI) and a minimum required signal- to-interference-plus-noise ratio (SINR). The globally optimal solution of the design problem is obtained via the semidefinite programming (SDP) relaxation approach. Interestingly, we can show that at most one dedicated energy beam is needed to achieve optimality. Numerical results demonstrate that with the proposed design a significant performance gain and improved fairness can be provided to the users compared to two baseline schemes

[C 50] Performance Analysis of a Hybrid Downlink-Uplink Cooperative NOMA Scheme

Z. Wei, L. Dai, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers accepted for publication, VTC 2017, Spring.

Abstract: This paper proposes a novel hybrid downlink- uplink cooperative NOMA (HDU-CNOMA) scheme to achieve a better tradeoff between spectral efficiency and signal reception reliability than the conventional cooperative NOMA schemes. In particular, the proposed scheme enables the strong user to perform a cooperative transmission and an interference-free uplink transmission simultaneously during the cooperative phase, at the expense of a slightly decrease in signal reception reliability at the weak user. We analyze the outage probability, diversity order, and outage throughput of the proposed scheme. Simulation results not only confirm the accuracy of the developed analytical results, but also unveil the spectral efficiency gains achieved by the proposed scheme over a baseline cooperative NOMA scheme and a non-cooperative NOMA scheme.

[C 51] Fairness Comparison of Uplink NOMA and OMA

Z. Wei, J. Guo, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers accepted for publication, VTC 2017, Spring.

Abstract: In this paper, we compare the resource allocation fairness of uplink communications between non-orthogonal mul- tiple access (NOMA) and orthogonal multiple access (OMA). Through characterizing the contribution of the individual user data rate to the system sum rate, we analyze the fundamental reasons that NOMA offers a more fair resource allocation than that of OMA in asymmetric channels. Furthermore, a fairness indicator metric based on Jain’s index is proposed to measure the asymmetry of multiuser channels. More importantly, the proposed metric provides a selection criterion for choosing between NOMA and OMA for fair resource allocation. Based on this discussion, we propose a hybrid NOMA-OMA scheme to further enhance the users fairness. Simulation results confirm the accuracy of the proposed metric and demonstrate the fair- ness enhancement of the proposed hybrid NOMA-OMA scheme compared to the conventional OMA and NOMA scheme.

[C 52] Multiuser Precoding and Channel Estimation for Hybrid Millimeter Wave Systems

L. Zhao, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers accepted for publication, IEEE ICC 2017.

Abstract

[C 53] Optimal Resource Allocation for Multicarrier MISO-NOMA Systems

Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers accepted for publication, IEEE ICC 2017.

Abstract

[C 54] Energy-Efficient Transmission for Wireless Powered D2D Communication Networks

Y. Zhang, J. Zhang, Y. Sun, and Derrick Wing Kwan Ng
Conference Papers accepted for publication, IEEE ICC 2017.

Abstract

[C 55] On the Performance of Wireless Powered Communication With Non-linear Energy Harvesting

R. Morsi, E. Boshkovaka, E. Ramadan, Derrick Wing Kwan Ng, and R. Schober
Conference Papers invited paper, IEEE SPAWC 2017.

Abstract: In this paper, we analyze the performance of a time-slotted multi-antenna wireless powered communication (WPC) system, where a wireless device first harvests radio frequency (RF) energy from a power station (PS) in the downlink to facilitate information transfer to an information receiving station (IRS) in the uplink. The main goal of this paper is to provide insights and guidelines for the design of practical WPC systems. To this end, we adopt a recently proposed parametric non-linear RF energy harvesting (EH) model, which has been shown to accurately model the end-to-end non-linearity of practical RF EH circuits. In order to enhance the RF power transfer efficiency, maximum ratio transmission is adopted at the PS to focus the energy signals on the wireless device. Furthermore, at the IRS, maximum ratio combining is used. We analyze the outage probability and the average throughput of information transfer, assuming Nakagami-$m$ fading uplink and downlink channels. Moreover, we study the system performance as a function of the number of PS transmit antennas, the number of IRS receive antennas, the transmit power of the PS, the fading severity, the transmission rate of the wireless device, and the EH time duration. In addition, we obtain a fixed point equation for the optimal transmission rate and the optimal EH time duration that maximize the asymptotic throughput for high PS transmit powers. All analytical results are corroborated by simulations.

[C 56] Resource Allocation for Secure Full-Duplex OFDMA Radio Systems

Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers invited paper, IEEE SPAWC 2017.

Abstract: In this paper, we study the resource allocation for an orthogonal frequency division multiple access (OFDMA) radio system employing a full-duplex base station for serving multiple half-duplex downlink and uplink users simultaneously. The resource allocation design objective is the maximization of the weighted system throughput while limiting the information leakage to guarantee secure simultaneous downlink and uplink transmission in the presence of potential eavesdroppers. The algorithm design leads to a mixed combinatorial non-convex optimization problem and obtaining the globally optimal solution entails a prohibitively high computational complexity. Therefore, an efficient successive convex approximation based suboptimal iterative algorithm is proposed. Our simulation results confirm that the proposed suboptimal algorithm achieves a significant performance gain compared to two baseline schemes.

[C 57] Non-orthogonal Multiple Access Full-Duplex Communication Systems

Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers invited paper, 21th International ITG Workshop on Smart Antennas (WSA) 2017.

Abstract

[C 58] Joint Power and Subcarrier Allocation for Multicarrier Full-Duplex Systems

Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers invited paper, ICASSP, 2017.

Abstract

[C 59] Secure SWIPT Networks Based on a Non-linear Energy Harvesting Model

E. Boshkovska, N. Zlatanov, L. Dai, Derrick Wing Kwan Ng, and R. Schober
Conference Papers IEEE WCNC, San Francisco, USA.

Abstract

[C 60] Cache-Enabled Physical-Layer Security for Video Streaming in Wireless Networks with Limited Backhaul

L. Xiang, Derrick Wing Kwan Ng, R. Schober, and V. W-S. Wong
Conference Papers accepted for presentation, 2016 IEEE Global Communications Conference: Workshops: 4th Workshop on Trusted Communications with Physical Layer Security, Dec. 2016.

Abstract

[C 61] Robust Optimization with Probabilistic Constraints for Power-Efficient and Secure SWIPT

T. A. Le, Q.-T. Vien, H. X. Nguyen, Derrick Wing Kwan Ng, and R. Schober
Conference Papers accepted for presentation at the IEEE Globecom. 2016, Washington, DC, USA, Dec. 2016.

Abstract:

[C 62] Power-Efficient Resource Allocation for MC-NOMA with Statistical Channel State Information

Z. Wei, Derrick Wing Kwan Ng, and J. Yuan
Conference Papers accepted for presentation at the IEEE Globecom. 2016, Washington, DC, USA, Dec. 2016.

Abstract

In this paper, we study the power-efficient resource allocation for multicarrier non-orthogonal multiple access (MCNOMA) systems. The resource allocation algorithm design is formulated as a non-convex optimization problem which takes into account the statistical channel state information at transmitter and quality of service (QoS) constraints. To strike a balance between system performance and computational complexity, we propose a suboptimal power allocation and user scheduling with low computational complexity to minimize the total power consumption. The proposed design exploits the heterogeneity of QoS requirement to determine the successive interference cancellation decoding order. Simulation results demonstrate that the proposed scheme achieves a close-to-optimal performance and significantly outperforms a conventional orthogonal multiple access (OMA) scheme.

[C 63] Spectrum-Power Trading for Energy-Efficient Small Cell

Q. Wu, G. Li, W. Chen, and Derrick Wing Kwan Ng
Conference Papers accepted for presentation at the IEEE Globecom. 2016, Washington, DC, USA, Dec. 2016.

Abstract

This paper investigates spectrum-power trading between a small cell (SC) and a macro-cell (MC), where the SC consumes power to serve the macro-cell users (MUs) in exchange for some bandwidth from the MC. Our goal is to maximize the system energy efficiency (EE) of the SC while guaranteeing the quality of service (QoS) of each MU as well as small cell users (SUs). Specifically, given the minimum data rate requirement and the bandwidth provided by the MC, the SC jointly optimizes MU selection, bandwidth allocation, and power allocation while guaranteeing its own minimum required system data rate. The problem is challenging due to the binary MU selection variables and the fractional form objective function. We first show that in order to achieve the maximum system EE, the bandwidth of an MU is shared with at most one SU in the SC. Then, for a given MU selection, the optimal bandwidth and power allocations are obtained by exploiting the fractional programming. To perform MU selection, we first introduce the concept of trading EE. Then, we reveal a sufficient and necessary condition for serving an MU without considering the total power constraint and the minimum data rate constraint. Based on this insight, we propose a low computational complexity MU selection algorithm. Simulation results demonstrate the effectiveness of the proposed algorithms.

[C 64] Optimal Joint Power and Subcarrier Allocation for MC-NOMA Systems

Y. Sun, Derrick Wing Kwan Ng, Z. Ding, and R. Schober
Conference Papers accepted for presentation at the IEEE Globecom. 2016, Washington, DC, USA, Dec. 2016.

Abstract

In this paper, we investigate the resource allocation algorithm design for multicarrier non-orthogonal multiple access (MC-NOMA) systems. The proposed algorithm is obtained from the solution of a non-convex optimization problem for the maximization of the weighted system throughput. We employ monotonic optimization to develop the optimal joint power and subcarrier allocation policy. The optimal resource allocation policy serves as a performance benchmark due to its high complexity. Furthermore, to strike a balance between computational complexity and optimality, a suboptimal scheme with low computational complexity is proposed. Our simulation results reveal that the suboptimal algorithm achieves a close-tooptimal performance and MC-NOMA employing the proposed resource allocation algorithm provides a substantial system throughput improvement compared to conventional multicarrier orthogonal multiple access (MC-OMA).

[C 65] Robust Resource Allocation for Full-Duplex Cognitive Radio Systems

Y. Sun, Derrick Wing Kwan Ng, N. Zlatanov, and R. Schober
Conference Papers invited paper, European Signal Processing Conference, Budapest, Aug. 2016.

Abstract

In this paper, we investigate resource allocation algorithm design for full-duplex (FD) cognitive radio systems. The secondary network employs a FD base station for serving multiple half-duplex downlink and uplink users simultaneously.We study the resource allocation design for minimizing the maximum interference leakage to primary users while providing quality of service for secondary users. The imperfectness of the channel state information of the primary users is taken into account for robust resource allocation algorithm design. The algorithm design is formulated as a non-convex optimization problem and solved optimally by applying semidefinite programming (SDP) relaxation. Simulation results not only show the significant reduction in interference leakage compared to baseline schemes, but also confirm the robustness of the proposed algorithm.

[C 66] Robust Beamforming for SWIPT Systems with Non-linear Energy Harvesting Model

E. Boshkovska, A. Koelpin, Derrick Wing Kwan Ng, N. Zlatanov, and R. Schober
Conference Papers invited paper, accepted for publication, IEEE 17th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Edinburgh, United Kingdom, Jul. 2016

Abstract

This paper investigates resource allocation for simultaneous wireless information and power transfer (SWIPT) downlink systems based on a non-linear energy harvesting model. The resource allocation algorithm design is formulated as a nonconvex optimization problem for the maximization of the total harvested power. The proposed problem formulation not only takes into account imperfect channel state information (CSI) but also guarantees the quality-of-service (QoS) of information transfer. A novel iterative algorithm is proposed to obtain the globally optimal solution of the considered non-convex optimization problem. In each iteration, a rank-constrained semidefinite program (SDP) is solved optimally by SDP relaxation. Simulation results demonstrate the significant gains in harvested power and the robustness against CSI imperfection for the proposed optimal resource allocation, compared to a baseline scheme designed for perfect CSI and the conventional linear energy harvesting model.

[C 67] Multi-Objective Resource Allocation in Full-Duplex SWIPT Systems

S. Leng, Derrick Wing Kwan Ng, N. Zlatanov, and R. Schober
Conference Papers accepted for publication at the IEEE ICC 2016, Malaysia, May 2016.

Abstract

In this paper, we investigate the resource allocation algorithm design for full-duplex simultaneous wireless information and power transfer (FD-SWIPT) systems. The considered system comprises a FD radio base station, multiple single-antenna half-duplex (HD) users, and multiple energy harvesters equipped with multiple antennas. We propose a multi-objective optimization framework to study the trade-off between uplink transmit power minimization, downlink transmit power minimization, and total harvested energy maximization. The considered optimization framework takes into account heterogeneous quality of service requirements for uplink and downlink communication and wireless power transfer. The non-convex multi-objective optimization problem is transformed into an equivalent rank-constrained semidefinite program (SDP) and solved optimally by SDP relaxation. The solution of the proposed framework results in a set of Pareto optimal resource allocation policies. Numerical results unveil an interesting trade-off between the considered conflicting system design objectives and reveal the improved power efficiency facilitated by FD in SWIPT systems compared to traditional HD systems.

[C 68] Low-Complexity MIMO Precoding with Discrete Signals and Statistical CSI

Y. Wu, C.-K. Wen, Derrick Wing Kwan Ng, R. Schober, and A. Lozano
Conference Papers accepted for publication at the IEEE ICC 2016, Malaysia, May 2016.

Abstract

In this paper, we investigate the design of multiple input multiple-output single-user precoders for finite-alphabet signals under the premise of statistical channel-state information at the transmitter. Based on an asymptotic expression for the mutual information of channels exhibiting antenna correlations, we propose a low-complexity iterative algorithm that radically reduces the computational load of existing approaches by orders of magnitude with only minimal losses in performance. The complexity savings increase with the number of transmit antennas and with the cardinality of the signal alphabet, making it possible to support values thereof that were unwieldy in existing solutions.

[C 69] Novel Protocol with Improved Outage Probability Performance for the Fading Two-Hop Half-Duplex Relay Channel

N. Zlatanov, V. Jamali, Derrick Wing Kwan Ng,and R. Schober
Conference Papers accepted for publication at the IEEE ICC 2016, Malaysia, May 2016.

Abstract

Based on the coding scheme recently introduced in [1], we propose new communication protocols with improved outage probability performance for the fading two-hop half-duplex (HD) relay channel. This channel is comprised of a source, a HD relay, and a destination, where a direct source-destination link does not exist. For this channel, we assume that the transmitting nodes do not have transmitter-side channel state information and therefore have to transmit with fixed rate. As a result, outages may occur. We propose protocols for the cases when feedback from receiving to transmitting nodes is not possible and restricted to one bit of feedback information per time slot, respectively. In the proposed protocols, the relay's silent symbol intervals, when the relay receives, carry information which improves the reliability of both the source-relay and relay-destination links. In contrast, in existing protocols, the relay's silent symbol intervals, when the relay receives, are a priori known to the destination and thereby cannot carry information. Our numerical results show that the proposed protocols achieve significant performance gains in terms of outage probability compared to existing protocols in the literature. These gains are only the result of using a different coding scheme than existing protocols.

[C 70] Power Allocation and Scheduling for SWIPT Systems with Non-linear Energy Harvesting Model

E. Boshkovska, R. Morsi, Derrick Wing Kwan Ng,and R. Schober
Conference Papers accepted for publication at the IEEE ICC 2016, Malaysia, May 2016.

Abstract

In this paper, we design a resource allocation algorithm for multiuser simultaneous wireless information and power transfer systems for a realistic non-linear energy harvesting (EH) model. In particular, the algorithm design is formulated as a non-convex optimization problem for the maximization of the long-term average total harvested power at EH receivers subject to quality of service requirements for information decoding receivers. To obtain a tractable solution, we transform the corresponding non-convex sum-of-ratios objective function into an equivalent objective function in parametric subtractive form. This leads to a computationally efficient iterative resource allocation algorithm. Numerical results reveal a significant performance gain that can be achieved if the resource allocation algorithm design is based on the non-linear energy harvesting model instead of the traditional linear model.

[C 71] Capacity of the Two-Hop Full-Duplex Relay Channel with Wireless Power Transfer from Relay to Battery-less Source

N. Zlatanov, Derrick Wing Kwan Ng,and R. Schober
Conference Papers accepted for publication at the IEEE ICC 2016, Malaysia, May 2016.

Abstract

In this paper, we investigate a communication system comprised of a wireless sensor which harvests radio frequency (RF) energy from a full-duplex relay node and exploits this energy to transmit data to a destination node via the relay node. Thereby, the relay has two functions. Namely, it transfers RF energy to the sensor via wireless power transfer and relays the information received from the sensor to the destination. Moreover, we assume that the sensor is too small to be equipped with a battery. As a result, the energy of each symbol transmitted by the sensor is limited by the energy harvested during the previous symbol interval. For this system model, we derive the capacity. Thereby, we show that in order to achieve the capacity, the sensor has to harvest the RF energy that reaches the sensor when the relay transmits information to the destination. As a result, the relay does not need to dedicate energy strictly for energy harvesting since the energy spent at the relay for information transfer can also be used by the sensor to harvest energy. In a numerical example, we compare the derived capacity to the rates of two benchmark schemes.

[C 72] Transmit Beamforming for QoE Improvement in C-RAN with Mobile Virtual Network Operators

Z. Wang, Derrick Wing Kwan Ng, V. W.S. Wong, and R. Schober
Conference Papers accepted for publication at the IEEE ICC 2016, Malaysia, May 2016.

Abstract

Network slicing enables mobile virtual network operators (MVNOs) to lease communication resources from a mobile network operator (MNO). The cloud radio access network (C-RAN) architecture reduces the capital and operational expenditures for the MNO and improves the quality of experience (QoE) for mobile users. In this paper, we propose a beamforming scheme to maximize the aggregate QoE of the mobile users served by an MVNO by coordinating multiple remote radio heads (RRHs) in a C-RAN. We model the QoE of each mobile user by a sigmoidal function and formulate the beamforming design as a non-convex optimization problem. By introducing an interference threshold, we first develop an iterative algorithm to determine a suboptimal solution of the original problem. Based on simulation results, we then show that a suitable interference threshold can be obtained in an off-line manner such that the suboptimal solution is a close-to-optimal solution of the original non-convex problem. Simulation results also show that the proposed scheme can significantly improve the aggregate QoE of the mobile users compared to the traditional design where the system sum rate is maximized.

[C 73] Multi-Objective Beamforming for Energy-Efficient SWIPT Systems

S. Leng, Derrick Wing Kwan Ng, N. Zlatanov, and R. Schober
Conference Papers accepted for publication, International Conference on Computing, Networking and Communications, USA, Feb. 2016.

image Received the Best Paper Award .

Abstract

In this paper, we study the resource allocation algorithm design for energy-efficient simultaneous wireless information and power transfer (SWIPT) systems. The considered system comprises a transmitter, an information receiver, and multiple energy harvesting receivers equipped with multiple antennas. We propose a multi-objective optimization framework to study the trade-off between the maximization of the energy efficiency of information transmission and the maximization of wireless power transfer efficiency. The proposed problem formulation takes into account the per antenna circuit power consumption of the transmitter and the imperfect channel state information of the energy harvesting receivers. The adopted nonconvex multi-objective optimization problem is transformed into an equivalent rank-constrained semidefinite program (SDP) and optimally solved by SDP relaxation. Numerical results unveil an interesting trade-off between the considered conflicting system design objectives and reveal the benefits of multiple transmit antennas for improving system energy efficiency.

[C 74] Power Efficient and Secure Full-Duplex Wireless Communication Systems

Derrick Wing Kwan Ng, Y. Sun, and R. Schober
Conference Papers invited paper, in Proc. of IEEE Conference on Communications and Network Security, Florence, Italy, Jul. 2015.

Abstract

In this paper, we study resource allocation for a full-duplex (FD) radio base station serving multiple half-duplex (HD) downlink and uplink users simultaneously. The considered resource allocation algorithm design is formulated as a non-convex optimization problem taking into account minimum required receive signal-to-interference-plus-noise ratios (SINRs) for downlink and uplink communication and maximum tolerable SINRs at potential eavesdroppers. The proposed optimization framework enables secure downlink and uplink communication via artificial noise generation in the downlink for interfering the potential eavesdroppers. We minimize the weighted sum of the total downlink and uplink transmit power by jointly optimizing the downlink beamformer, the artificial noise covariance matrix, and the uplink transmit power. We adopt a semidefinite programming (SDP) relaxation approach to obtain a tractable solution for the considered problem. The tightness of the SDP relaxation is revealed by examining a sufficient condition for the global optimality of the solution. Simulation results demonstrate the excellent performance achieved by the proposed scheme and the significant transmit power savings enabled optimization of the artificial noise covariance matrix.

[C 75] Cross-Layer Optimization of Fast Video Delivery in Cache-Enabled Relaying Networks

L. Xiang Derrick Wing Kwan Ng, T. Islam, R. Schober, and V. W.S. Wong
Conference Papers accepted for publication at the IEEE Globeocm 2015, Dec. 2015.

Abstract

This paper investigates the cross-layer optimization of fast video delivery and caching for minimization of the overall video delivery time in a two-hop relaying network. The half-duplex relay nodes are equipped with both a cache and a buffer which facilitate joint scheduling of fetching and delivery to exploit the channel diversity for improving the overall delivery performance. The fast delivery control is formulated as a two-stage functional non-convex optimization problem. By exploiting the underlying convex and quasi-convex structures, the problem can be solved exactly and efficiently by the developed algorithm. Simulation results show that significant caching and buffering gains can be achieved with the proposed framework, which translates into a reduction of the overall video delivery time. Besides, a trade-off between caching and buffering gains is unveiled.

[C 76] Effective Rate Analysis of MISO Systems over alpha-mu Fading Channels

J. Zhang, L. Dai, Z. Wang Derrick Wing Kwan Ng, and W. Gerstacker
Conference Papers accepted for publication at the IEEE Globeocm 2015, Dec. 2015.

Abstract

[C 77] Multi-Objective Optimization for Power Efficient Full-Duplex Wireless Communication Systems

Y. Sun, Derrick Wing Kwan Ng, and R. Schober
Conference Papers accepted for publication at the IEEE Globeocm 2015, Dec. 2015.

Abstract

In this paper, we investigate power efficient resource allocation algorithm design for multiuser wireless communication systems employing a full-duplex (FD) radio base station for serving multiple half-duplex (HD) downlink and uplink users simultaneously. We propose a multi-objective optimization framework for achieving two conflicting yet desirable system design objectives, i.e., total downlink transmit power minimization and total uplink transmit power minimization, while guaranteeing the quality-of-service of all users. To this end, the weighted Tchebycheff method is adopted to formulate a multi-objective optimization problem (MOOP). Although the considered MOOP is non-convex, we solve it optimally by semidefinite programming relaxation. Simulation results not only unveil the trade-off between the total downlink and the total uplink transmit power, but also confirm that the proposed FD system provides substantial power savings over traditional HD systems.

A multiuser communication system with a full-duplex (FD) radio base station (BS), K=1 half-duplex (HD) downlink users, and J=1 HD uplink users. The BS is equipped with N_{\mathrm{T}} antennas for simultaneous uplink and downlink communication.

[C 78] Optimal Multiuser Scheduling Schemes for Simultaneous Wireless Information and Power Transfer

M. Chynonova, R. Morsi, Derrick Wing Kwan Ng, and R. Schober
Conference Papers invited paper, the 23rd European conference on Signal Processing (EUSIPCO 2015), Nice, France, Sep. 2015.

Abstract

In this paper, we study the downlink multiuser scheduling problem for systems with simultaneous wireless information and power transfer (SWIPT). We design optimal scheduling algorithms that maximize the long-term average system throughput under different fairness requirements, such as proportional fairness and equal throughput fairness. In particular, the algorithm designs are formulated as non-convex optimization problems which take into account the minimum required average sum harvested energy in the system. The problems are solved by using convex optimization techniques and the proposed optimization framework reveals the tradeoff between the long-term average system throughput and the sum harvested energy in multiuser systems with fairness constraints. Simulation results demonstrate that substantial performance gains can be achieved by the proposed optimization framework compared to existing suboptimal scheduling algorithms from the literature.

The average system sum rate (bit-per-channel use) versus the average sum harvested energy per time for different numbers of receivers N and for maximum throughput (MT), proportional fair (PF) scheduler, and equal throughput scheduler (ET).

[C 79] Resource Allocation for Outdoor-to-Indoor Multicarrier Transmission with Shared UE-side Distributed Antenna Systems

M. Breiling, Derrick Wing Kwan Ng, C. Rohde, F. Burkhardt and R. Schober
Conference Papers accepted for publication, the IEEE Vehicular Technology Conference (VTC) Spring, Glasgow, Scotland, UK, May 2015.

Abstract

In this paper, we study the resource allocation algorithm design for downlink multicarrier transmission with a shared user equipment (UE)-side distributed antenna system (SUDAS) which utilizes both licensed and unlicensed frequency bands for improving the system throughput. The joint UE selection and transceiver processing matrix design is formulated as a non-convex optimization problem for the maximization of the end-to-end system throughput (bits/s). In order to obtain a tractable resource allocation algorithm, we first show that the optimal transmitter precoding and receiver post-processing matrices jointly diagonalize the end-to-end communication channel. Subsequently, the optimization problem is converted to a scalar optimization problem for multiple parallel channels, which is solved by using an asymptotically optimal iterative algorithm. Simulation results illustrate that the proposed resource allocation algorithm for the SUDAS achieves an excellent system performance and provides a spatial multiplexing gain for single-antenna UEs.

belterralizard1 belterralizard2

Downlink communication system model with a base station (BS), K = 3 user equipments (UEs), and M = 3 SUDACs. The backend links use a licensed frequency band and the frontend links use an unlicensed frequency band such as the millimeter wave band (e.g. ~ 60 GHz).

[C 80] Secure Massive MIMO Transmission in the Presence of an Active Eavesdropper

Y. Wu, R. Schober, Derrick Wing Kwan Ng, C. Xiao, and G. Caire
Conference Papers accepted for publication, the IEEE International Conference on Communications (ICC) 2015, London, UK.

Abstract

In this paper, we investigate secure and reliable transmission strategies for multi-cell multi-user massive multiple-input multiple-output (MIMO) systems in the presence of an active eavesdropper. We consider a time-division duplex system where uplink training is required and an active eavesdropper can attack the training phase to cause pilot contamination at the transmitter. This forces the precoder used in the subsequent downlink transmission phase to implicitly beamform towards the eavesdropper, thus increasing its received signal power. We derive an asymptotic achievable secrecy rate for matched filter precoding and artificial noise (AN) generation at the transmitter when the number of transmit antennas goes to infinity. For the achievability scheme at hand, we obtain the optimal power allocation policy for the transmit signal and the AN in closed form. For the case of correlated fading channels, we show that the impact of the active eavesdropper can be completely removed if the transmit correlation matrices of the users and the eavesdropper are orthogonal. Inspired by this result, we propose a precoder null space design exploiting the low rank property of the transmit correlation matrices of massive MIMO channels, which can significantly degrade the eavesdropping capabilities of the active eavesdropper.

[C 81] Energy-Efficient Transmission for Wireless Powered Multiuser Communication Networks

Q. Wu, M. Tao, Derrick Wing Kwan Ng, W. Chen, and R. Schober
Conference Papers accepted for publication, the IEEE International Conference on Communications (ICC),London, UK. 2015.

Abstract

This paper considers the wireless powered communication networks, where a power station is proposed as a supplement for existing mobile networks to supply users with energy needed for information transmission. Specifically, we jointly optimize the time allocation and the power control in both the downlink and the uplink to maximize the system energy efficiency while guaranteeing the minimum system throughput. Exploiting fractional programming theory, we transform the non-convex energy efficiency maximization problem into a more tractable form. We then characterize the optimal structure of time allocation and power control, and propose an efficient algorithm to obtain the optimal solution. It is found that in the energy transfer stage, the power station always transmits with the maximum allowed power. Moreover, it is not necessary for all users to transmit signals in the information transmission stage, and users that are scheduled, deplete all of their energy. In addition, the maximal system energy efficiency can always be achieved by depleting all the available time. Numerical results demonstrate the effectiveness of the proposed energy-efficient design and suggests that it can achieve higher energy efficiency gain with more wireless powered receivers and smaller energy transfer distance, compared with the throughput optimal design

[C 82] Max-min Fair Wireless Energy Transfer for Secure Multiuser Communication Systems

Derrick Wing Kwan Ng and R. Schober
Conference Papers invited paper, IEEE Information Theory Workshop 2014, Hobart, Tasmania, Australia, Nov. 2014.

Abstract

This paper considers max-min fairness for wireless energy transfer in a downlink multiuser communication system. Our resource allocation design maximizes the minimum harvested energy among multiple multiple-antenna energy harvesting receivers (potential eavesdroppers) while providing quality of service (QoS) for secure communication to multiple single-antenna information receivers. In particular, the algorithm design is formulated as a non-convex optimization problem which takes into account a minimum required signal-to-interference-plus-noise ratio (SINR) constraint at the information receivers and a constraint on the maximum tolerable channel capacity achieved by the energy harvesting receivers for a given transmit power budget. The proposed problem formulation exploits the dual use of artificial noise generation for facilitating efficient wireless energy transfer and secure communication. A semidefinite programming (SDP) relaxation approach is exploited to obtain a global optimal solution of the considered problem. Simulation results demonstrate the significant performance gain in harvested energy that is achieved by the proposed optimal scheme compared to two simple baseline schemes.

Downlink SWIPT communication system model with K = 2 single- antenna information receivers and J = 2 multiple-antenna energy harvesting receivers.

[C 83] Resource Allocation for Coordinated Multipoint Networks with Wireless Information and Power Transfer

Derrick Wing Kwan Ng and R. Schober
Conference Papers accepted for publication at the IEEE Globecom 2014, Austin, TX, USA, Dec. 2014.

Abstract

This paper studies the resource allocation algorithm design for multiuser coordinated multipoint (CoMP) networks with simultaneous wireless information and power transfer (SWIPT). In particular, remote radio heads (RRHs) are connected to a central processor (CP) via capacity-limited backhaul links to facilitate CoMP joint transmission. Besides, the CP transfers energy to the RRHs for more efficient network operation. The considered resource allocation algorithm design is formulated as a non-convex optimization problem with a minimum required signal-to-interference-plus-noise ratio (SINR) constraint at multiple information receivers and a minimum required power transfer constraint at the energy harvesting receivers. By optimizing the transmit beamforming vectors at the CP and energy sharing between the CP and the RRHs, we aim at jointly minimizing the total network transmit power and the maximum capacity consumption per backhaul link. The resulting non-convex optimization problem is NP-hard. In light of the intractability of the problem, we reformulate it by replacing the non-convex objective function with its convex hull, which enables the derivation of an efficient iterative resource allocation algorithm. In each iteration, a non-convex optimization problem is solved by semi-definite programming (SDP) relaxation and the proposed iterative algorithm converges to a local optimal solution of the original problem. Simulation results illustrate that our proposed algorithm achieves a close-to-optimal performance and provides a significant reduction in backhaul capacity consumption compared to full cooperation. Besides, the considered CoMP network is shown to provide superior system performance as far as power consumption is concerned compared to a traditional system with multiple antennas co-located.

[C 84] Power Efficient and Secure Multiuser Communication Systems with Wireless Information and Power Transfer

S. Leng, Derrick Wing Kwan Ng, and R. Schober
Conference Papers in Proc. of IEEE International Conference on Communications (ICC) 2014, Sydney, Australia, Jun. 2014.

Abstract

In this paper, we study resource allocation algorithm design for power efficient secure communication with simultaneous wireless information and power transfer (WIPT) in multiuser communication systems. In particular, we focus on power splitting receivers which are able to harvest energy and decode information from the received signals. The considered problem is modeled as an optimization problem which takes into account a minimum required signal-to-interference-plus-noise ratio (SINR) at multiple desired receivers, a maximum tolerable data rate at multiple multi-antenna potential eavesdroppers, and a minimum required power delivered to the receivers. The proposed problem formulation facilitates the dual use of artificial noise in providing efficient energy transfer and guaranteeing secure communication. We aim at minimizing the total transmit power by jointly optimizing transmit beamforming vectors, power splitting ratios at the desired receivers, and the covariance of the artificial noise. The resulting non-convex optimization problem is transformed into a semidefinite programming (SDP) and solved by SDP relaxation. We show that the adopted SDP relaxation is tight and achieves the global optimum of the original problem. Simulation results illustrate the significant power saving obtained by the proposed optimal algorithm compared to suboptimal baseline schemes.

[C 85] Secure Layered Transmission in Multicast Systems with Wireless Information and Power Transfer

Derrick Wing Kwan Ng, R. Schober, and H. Alnuweiri
Conference Papers accepted for presentation at the IEEE International Conference on Communications (ICC), Sydney, Australia, 2014.

Abstract

This paper considers downlink multicast transmit beamforming for secure layered transmission systems with wireless simultaneous information and power transfer. We study the power allocation algorithm design for minimizing the total transmit power in the presence of passive eavesdroppers and energy harvesting receivers. The algorithm design is formulated as a non-convex optimization problem. Our problem formulation promotes the dual use of energy signals in providing secure communication and facilitating efficient energy transfer. Besides, we take into account a minimum required power for energy harvesting at the idle receivers and heterogeneous quality of service (QoS) requirements for the multicast video receivers. In light of the intractability of the problem, we reformulate the considered problem by replacing a non-convex probabilistic constraint with a convex deterministic constraint which leads to a smaller feasible solution set. Then, a semidefinite programming relaxation (SDR) approach is adopted to obtain an upper bound solution for the reformulated problem. Subsequently, sufficient conditions for the global optimal solution of the reformulated problem are revealed. Furthermore, we propose two suboptimal power allocation schemes based on the upper bound solution. Simulation results demonstrate the excellent performance and significant transmit power savings achieved by the proposed schemes compared to isotropic energy signal generation. .

[C 86] Power Efficient MISO Beamforming for Secure Layered Transmission

Derrick Wing Kwan Ng, R. Schober, and H. Alnuweiri
Conference Papers in Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Istanbul, Turkey, 2014.

Abstract

This paper studies secure layered video transmission in a multiuser multiple-input single-output (MISO) beamforming downlink communication system. The power allocation algorithm design is formulated as a non-convex optimization problem for minimizing the total transmit power while guaranteeing a minimum received signal-to-interference-plus-noise ratio (SINR) at the desired receiver. In particular, the proposed problem formulation takes into account the self-protecting architecture of layered transmission and artificial noise generation to prevent potential information eavesdropping. A semi-definite programming (SDP) relaxation based power allocation algorithm is proposed to obtain an upper bound solution. A sufficient condition for the global optimal solution is examined to reveal the tightness of the upper bound solution. Subsequently, two suboptimal power allocation schemes with low computational complexity are proposed for enabling secure layered video transmission. Simulation results demonstrate significant transmit power savings achieved by the proposed algorithms and layered transmission compared to the baseline schemes. .

[C 87] Power Allocation for a Hybrid Energy Harvesting Relay System with Imperfect Channel and Energy State Information

I. Ahmed, A. Ikhlef, Derrick Wing Kwan Ng, and R. Schober
Conference Papers in Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Istanbul, Turkey, 2014.

Abstract

In this paper, we consider both channel state uncertainty and harvested energy state uncertainty for a source??œrelay?? destination communication link where the source and the relay are equipped with hybrid energy sources. Taking into account these uncertainties is of important for practical energy harvesting (EH) communication. While channel state uncertainties also affect conventional communication systems and have been widely studied, harvested energy state uncertainties are specific to energy harvesting systems and have not been considered in the literature before. The considered hybrid energy sources include a constant energy source and an energy harvester. Our objective is to maximize the worst case system throughput over a finite number of transmission intervals.We propose robust optimal offline, optimal online, and suboptimal online power allocation schemes. The offline power allocation design is formulated as an optimization problem which can be solved optimally. For the online case, we propose a dynamic programming (DP) approach to compute the optimal transmit power. To alleviate the prohibitively high complexity inherent to DP, we also propose several suboptimal low??œcomplexity online power allocation schemes. Simulation results confirm the robustness of the proposed power allocation schemes to channel and energy state uncertainties.

[C 88] Optimal Resource Allocation for Energy Harvesting Two-way Relay Systems with Channel Uncertainty

I. Ahmed, A. Ikhlef, Derrick Wing Kwan Ng, and R. Schober
Conference Papers in Proceedings of the IEEE Global Conference on Signal and Information Processing, Austin, Texas, USA, Dec. 2013.

Abstract

In this paper, we consider two-way decode-and-forward (DF) multiple access and time division broadcasting relaying protocols with energy harvesting (EH) nodes. We propose optimal offline joint energy and transmission time allocation schemes for the considered relaying protocols taking into account channel state uncertainty. The proposed joint energy and transmission time allocation schemes are obtained based on convex optimization problems and maximize the aggregate system throughput over a finite number of transmission intervals.We compare the optimal throughputs obtained for the multiple access and time division broadcasting protocols via simulations. Our results reveal that the proposed schemes are robust to imperfect channel state information and that multiple access broadcasting is less affected by low harvesting rate at the relay than time division broadcasting. .

[C 89] Multi-Objective Beamforming for Secure Communication in Systems with Wireless Information and Power Transfer

Derrick Wing Kwan Ng, Lin Xiang and R. Schober
Conference Papers invited paper, in Proceedings of the IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), special session on physical layer security, Jun., 2013.

Abstract

In this paper, we study power allocation for secure communication in a multiuser multiple-input single-output (MIS- O) downlink system with simultaneous wireless information and power transfer. The receivers are able to harvest energy from the radio frequency when they are idle. We propose a multi- objective optimization problem for power allocation algorithm design which incorporates two conflicting system objectives: total transmit power minimization and energy harvesting efficiency maximization. The proposed problem formulation takes into account a quality of service (QoS) requirement for the system secrecy capacity. Our designs advocate the dual use of artificial noise in providing secure communication and facilitating efficient energy harvesting. The multi-objective optimization problem is non-convex and is solved by a semidefinite programming (SDP) relaxation approach which results in an approximate of solution. A sufficient condition for the global optimal solution is revealed and the accuracy of the approximation is examined. To strike a balance between computational complexity and system performance, we propose two suboptimal power allocation schemes. Numerical results not only demonstrate the excellent performance of the proposed suboptimal schemes compared to baseline schemes, but also unveil an interesting trade-off between energy harvesting efficiency and total transmit power. .

[C 90] Resource Allocation for Secure Communication in Systems with Wireless Information and Power Transfer

Derrick Wing Kwan Ng and R. Schober
Conference Papers in Proceedings of the IEEE Globecom 2013 - Workshop on Trusted Communications with Physical Layer Security, Atlanta, USA.

Abstract

In this paper, we study power allocation for secure communication in a multiuser multiple-input single-output (MISO) downlink system with simultaneous wireless information and power transfer. The receivers are able to harvest energy from the radio frequency when they are idle. We propose a multi- objective optimization problem for power allocation algorithm design which incorporates two conflicting system objectives: total transmit power minimization and energy harvesting efficiency maximization. The proposed problem formulation takes into account a quality of service (QoS) requirement for the system secrecy capacity. Our designs advocate the dual use of artificial noise in providing secure communication and facilitating efficient energy harvesting. The multi-objective optimization problem is non-convex and is solved by a semidefinite programming (SDP) relaxation approach which results in an approximate of solution. A sufficient condition for the global optimal solution is revealed and the accuracy of the approximation is examined. To strike a balance between computational complexity and system performance, we propose two suboptimal power allocation schemes. Numerical results not only demonstrate the excellent performance of the proposed suboptimal schemes compared to baseline schemes, but also unveil an interesting trade-off between energy harvesting efficiency and total transmit power. .

[C 91] Optimal Storage-Aided Wind Generation Integration Considering Ramping Requirements

L. Xiang, Derrick Wing Kwan Ng, W. Lee, and R. Schober
Conference Papers in Proceedings of the 4th IEEE International Conference on Smart Grid Communications, Vancouver, Canada, pp. 648-653 Oct. 2013.

Abstract

Large-scale integration of intermittent wind energy can put a large burden on the utility company in balancing system demand and supply. As more and more dispersed wind energy suppliers connect to the system for electricity supply, the power system suffers from increased operation cost and risk caused by the discrepant interests of energy suppliers and the utility company. Energy suppliers may only concern about maximizing their own proï¬?ts by pushing as much energy into the grid as possible, while neglecting the risk of steep ramps in wind generation. In this paper, exploiting the two-way communication capability in smart grid, we propose interactive ramp control of wind energy integration by aligning the individual pursuits of the energy suppliers and the utility company for social welfare maximization. The optimal wind energy integration and generator ramp control are investigated in an offline social welfare optimization problem assuming full knowledge of future wind energy and load demand. Moreover, the benefits of storage are exploited in our proposed storage-aided generation range adaption scheme to reduce the potential risk caused by inaccurate wind energy forecasts and the ramping latency of slow generators. Furthermore, a suboptimal storage-aided generation range adaption scheme with low computational complexity is presented for online control of wind integration when wind energy forecasts are unavailable. Our simulation results show that interactive ramp control is necessary to achieve efficient and secure wind energy integration and with the aid of storage, the power system??¢s ramping capability can be improved at lower operation cost.

[C 92] Spectral Efficient Optimization in OFDM Systems with Wireless Information and Power Transfer

Derrick Wing Kwan Ng and R. Schober
Conference Papers invited paper, in Proceedings of the 21st European Signal Processing Conference, Marrakech, Morocco, Sep. 2013.

Abstract

This paper considers an orthogonal frequency division multiplexing (OFDM) point-to-point wireless communication system with simultaneous wireless information and power transfer. We study a receiver which is able to harvest energy from the desired signal, noise, and interference. In particular, we consider a power splitting receiver which dynamically splits the received power into two power streams for information decoding and energy harvesting. We design power allocation algorithms maximizing the spectral efficiency (bit/s/Hz) of data transmission. In particular, the algorithm design is formulated as a nonconvex optimization problem which takes into account the constraint on the minimum power delivered to the receiver. The problem is solved by using convex optimization techniques and a one-dimensional search. The optimal power allocation algorithm serves as a system benchmark scheme due to its high complexity. To strike a balance between system performance and computational complexity, we also propose two suboptimal algorithms which require a low computational complexity. Simulation results demonstrate the excellent performance of the proposed suboptimal algorithms.

[C 93] Energy-Efficient Resource Allocation in Multiuser OFDM Systems with Wireless Information and Power Transfer

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Conference Papersin Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC) 2013, Shanghai, China, pp. 3823 - 3828, Apr. 2013.

Abstract

In this paper, we study the resource allocation algorithm design for multiuser orthogonal frequency division multiplexing (OFDM) downlink systems with simultaneous wireless information and power transfer. The algorithm design is formulated as a non-convex optimization problem for maximizing the energy efficiency of data transmission (bit/Joule delivered to the users). In particular, the problem formulation takes into account the minimum required system data rate, heterogeneous minimum required power transfers to the users, and the circuit power consumption. Subsequently, by exploiting the method of time-sharing and the properties of nonlinear fractional programming, the considered non-convex optimization problem is solved using an efficient iterative resource allocation algorithm. For each iteration, the optimal power allocation and user selection solution are derived based on Lagrange dual decomposition. Simulation results illustrate that the proposed iterative resource allocation algorithm achieves the maximum energy efficiency of the system and reveal how energy efficiency, system capacity, and wireless power transfer benefit from the presence of multiple users in the system.

[C 94] Energy-Efficient Resource Allocation in OFDM Systems with Wireless Information and Power Transfer

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Conference Papersin Proceedings of the IEEE International Conference on Communications (ICC) 2013 - SAC - Green Communication Systems and Networks, Budapest, Hungary, pp. 4125 - 4130, Jun. 2013.

Abstract

This paper considers an orthogonal frequency division multiplexing (OFDM) downlink point-to-point system with simultaneous wireless information and power transfer. It is assumed that the receiver is able to harvest energy from noise, interference, and the desired signals. We study the design of power allocation algorithms maximizing the energy efficiency of data transmission (bit/Joule delivered to the receiver). In particular, the algorithm design is formulated as a high-dimensional nonconvex optimization problem which takes into account the circuit power consumption, the minimum required data rate, and a constraint on the minimum power delivered to the receiver. Subsequently, by exploiting the properties of nonlinear fractional programming, the considered non-convex optimization problem, whose objective function is in fractional form, is transformed into an equivalent optimization problem having an objective function in subtractive form, which enables the derivation of an efficient iterative power allocation algorithm. In each iteration, the optimal power allocation solution is derived based on dual decomposition and a one-dimensional search. Simulation results illustrate that the proposed iterative power allocation algorithm converges to the optimal solution, and unveil the trade-off between energy efficiency, system capacity, and wireless power transfer: (1) In the low transmit power regime, maximizing the system capacity may maximize the energy efficiency. (2) Wireless power transfer can enhance the energy efficiency, especially in the interference limited regime.

[C 95] Optimal Power Allocation for a Hybrid Energy Harvesting Transmitter

I. Ahmed, A. Ikhlef, Derrick Wing Kwan Ng, and R. Schober
Conference Papersin Proceedings of the IEEE ICC 2013 - SAC - Green Communication Systems and Networks, Budapest, Hungary, 4185 - 4190, Jun. 2013.

Abstract

In this work, we consider a point??œto??œpoint link where the transmitter has a hybrid supply of energy, i.e., the energy is supplied by a constant energy source and an energy harvester, which harvests energy from its surrounding environment. Our goal is to jointly minimize the power consumed by the constant energy source and any possible waste of the harvested energy to ensure their optimum utilization for transmission of a given amount of data in a given number of time intervals. Two scenarios are considered for packet arrival. In the ï¬?rst scenario, we assume that all data packets have arrived before the transmission begins, whereas in the second scenario, we assume that data packets are arriving during the course of data transmission. For both scenarios, we propose optimal offline transmit power allocation schemes which provide insight on how to efficiently consume the energy supplied by the constant energy source and the energy harvester.

[C 96] Energy-Efficient Power Allocation for M2M Communications with Energy Harvesting Transmitter

Derrick Wing Kwan Ng and R. Schober
Conference Papersin Proceedings of the IEEE Global Communications Conference (Globecom) 2012 Workshop on Machine-to-Machine Communications, pp. 1644 - 1649, Dec. 2012.

Abstract

In this paper, power allocation for energy-efficient point-to-point machine-to-machine (M2M) communication systems with multiple energy harvesting sources is studied. Under a deterministic system setting, we formulate the power allocation problem as a non-convex optimization problem over a finite horizon taking into account the circuit energy consumption, finite battery storage capacities, and a minimum required data rate. The considered non-convex optimization problem is transformed into a convex optimization problem by exploiting the properties of fractional programming which results in an efficient optimal off-line iterative power allocation algorithm. In each iteration, the transformed problem is solved by using dual decomposition and a recursive power allocation solution is obtained for maximization of the energy efficiency of data transmission (bit/Joule delivered to the receiver).

[C 97] Hybrid Visible Light Communications in Intelligent Transportation Systems with Position Based Services

J. Liu, P. W. C. Chan, Derrick Wing Kwan Ng, Ernest S. Lo, S. Shimamoto
Conference Papersin Proceedings of the IEEE Global Communications Conference (Globecom) 2012 Workshop on Optical Wireless Communications (OWC), Anaheim, USA, pp. 1254 - 1259 , Dec. 2012.

Abstract

This paper proposes a hybrid communication system for Intelligent Transportation System (ITS) utilizing visible light and radio communications for position-based services. The directionality of light communication is used to distribute position based keys to vehicles such that they can extract information related only to their desired lanes. The extended coverage of radio communication is used to provide stable data communication complementing the visible light communications (VLC) systems. This paper provides system models and important parameters for designing a hybrid ITS system. The system performance is evaluated by simulation, and the results demonstrate a considerable increase of the effective communication area and receivable information using the proposed hybrid ITS system compared with a VLC system.

[C 98] Spectral Efficiency in Large-Scale MIMO-OFDM Systems with Per-Antenna Power Cost

Derrick Wing Kwan Ng and R. Schober
Conference Papersinvited paper, in Proceedings of the Asilomar Conference on Signals, Systems, and Computers, Monterey, CA, USA, pp. 289 - 294, Nov. 2012.

Abstract

In this paper, resource allocation for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) downlink networks with large numbers of base station antennas is studied. Assuming perfect channel state information at the transmitter, the resource allocation algorithm design is modeled as a non-convex optimization problem which takes into account the joint power consumption of the power amplifiers, antenna unit, and signal processing circuit unit. Subsequently, by exploiting the law of large numbers and dual decomposition, an efficient suboptimal iterative resource allocation algorithm is proposed for maximization of the system capacity (bit/s). In particular, closed-form power allocation and antenna allocation policies are derived in each iteration. Simulation results illustrate that the proposed iterative resource allocation algorithm achieves a close-to-optimal performance in a small number of iterations and unveil a trade-off between system capacity and the number of activated antennas: Activating all antennas may not be a good solution for system capacity maximization when a system with a per antenna power cost is considered.

[C 99] Tomlinson-Harashima Precoding for Multiuser MIMO Systems with Quantized CSI Feedback

L. Sun, M. Leit, and Derrick Wing Kwan Ng
Conference Papersinvited paper, in Proceedings of the Asilomar Conference on Signals, Systems, and Computers, Monterey, CA, USA, pp. 1846 - 1850, Nov. 2012.

Abstract

This paper considers the implementation of Tomlinson-Harashima (TH) precoding for multiuser MIMO systems based on quantized channel state information (CSI) at the transmitter side. Compared with the results in [1], our scheme applies to more general system setting where the number of users in system K can be not equal to the number of transmit antenna nT (K ??nT). We also study the achievable average sum rate of the proposed quantized CSI feedback-based TH precoding scheme. The expression of an upper bound on the mean loss in sum rate due to CSI quantization is derived.We also present some numerical results. Both the analytical and numerical results show that nonlinear precoding suffers from imperfect CSI more greatly than linear precoding. Nonlinear TH precoding can achieve much better performance than that of linear zero-forcing precoding for both perfect CSI and quantized CSI cases. In addition, our derived upper bound for TH precoding converges to the true rate loss faster than the upper bound for zero-forcing precoding obtained in [2] as the number of feedback bits increases.

[C 100] Energy-Efficient Resource Allocation in Multi-Cell OFDMA Systems with Limited Backhaul

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Conference Papersinvited paper, Third Nordic Workshop on System & Network Optimization for Wireless 2012, Trysil, Norway, pp. 1-2, Apr. 2012.

Abstract

We study resource allocation for energy efficient communication in multi-cell orthogonal frequency division multiple access (OFDMA) downlink networks with cooperative base stations (BSs). We formulate the resource allocation problem for joint BS transmission as a non-convex optimization problem which takes into account the circuit power consumption, the limited backhaul capacity, and the minimum required data rate. By using the concept of perturbation function, we show that the duality gap for the considered problem is zero under some general conditions, despite the non-convexity of the primal problem. Thus, dual decomposition can be used to derive an efficient closed-form power allocation solution for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users).

[C 101] Energy-Efficient Resource Allocation in OFDMA Systems with Large Numbers of Base Station Antennas

Derrick Wing Kwan Ng and R. Schober
Conference Papersin Proceedings of the IEEE International Conference on Communications (ICC) 2012 Workshop on Green Communications and Networking, Ottawa, Canada, pp. 5916 - 5920, Jun. 2012.

Abstract

In this paper, resource allocation for energy efficient communication in orthogonal frequency division multiple access (OFDMA) downlink networks with large numbers of base station (BS) antennas is studied. Assuming perfect channel state information at the transmitter (CSIT), the resource allocation algorithm design is modelled as a non-convex optimization problem for maximizing the energy efficiency of data transmission (bit/Joule delivered to the users), where the circuit power consumption and a minimum required data rate are taken into consideration. Subsequently, by exploiting the properties of fractional programming, an efficient iterative resource allocation algorithm is proposed to solve the problem. In particular, the power allocation, subcarrier allocation, and antenna allocation policies for each iteration are derived. Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations and unveil the trade-off between energy efficiency and the number of antennas.

[C 102] Energy-Efficient Resource Allocation in SDMA Systems with Large Numbers of Base Station Antennas

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Conference Papersin Proceedings of the IEEE International Conference on Communications (ICC) 2012, Ottawa, Canada, pp. 4027 - 4032. 2012.

Abstract

In this paper, resource allocation for energy efficient communication in space division multiple access (SDMA) downlink networks with large numbers of transmit antennas is studied. The considered problem is modelled as a non-convex optimization problem which takes into account the circuit power consumption and a minimum required data rate. By exploiting the properties of fractional programming, the considered non-convex optimization problem in fractional form is transformed into an equivalent optimization problem in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. The optimal power allocation solution for each iteration is derived based on a low complexity user selection policy for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations and unveil the trade-off between energy efficiency and the number of antennas.

[C 103] Energy-Efficient Resource Allocation in Multi-Cell OFDMA Systems with Limited Backhaul

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Conference Papers in Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Paris, France, pp. 1146 - 1151, Apr. 2012.

image Received the Best Paper Award in PHY and Fundamentals Symposium .

Abstract

In this paper, resource allocation for energy efficient communication in multi-cell orthogonal frequency division multiple access (OFDMA) downlink networks with cooperative base stations (BSs) is studied. The considered problem is formulated as a non-convex optimization problem which takes into account the circuit power consumption, the limited backhaul capacity, and the minimum required data rate for joint BS zero-forcing beamforming (ZFBF) transmission. By exploiting the properties of fractional programming, the considered non-convex optimization problem in fractional form is transformed into an equivalent optimization problem in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. For each iteration, the optimal power allocation solution is derived with a low complexity suboptimal subcarrier allocation policy for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations, and unveil the trade-off between energy efficiency and network capacity.

[C 104] Resource Allocation for Secure OFDMA Networks with Imperfect CSIT

Derrick Wing Kwan Ng, Ernest S. Lo, and R. Schober
Conference Papersin Proceedings of the IEEE Global Communications Conference (Globecom), Houston, Texas, USA, pp. 1-6, Dec. 2011.

image Received the Best Paper Award in Wireless Communications Symposium .

Abstract

In this paper, we formulate an optimization problem for resource allocation and scheduling in orthogonal frequency division multiple access (OFDMA) networks. Our problem formulation takes into account artificial noise generation to combat a passive multiple antenna eavesdropper and the effects of imperfect channel state information at the transmitter (CSIT) in slow fading. The optimization problem is solved by dual decomposition which results in an iterative resource allocation algorithm with a fast speed of convergence. The packet data rate, secrecy data rate, power, and subcarrier allocation policies are optimized to maximize the average secrecy outage capacity (bit/s/Hz securely and successfully delivered to the users). Simulation results illustrate that our proposed iterative algorithm converges to the optimal solution in a small number of iterations and guarantees a non-zero secrecy data rate for given target secrecy outage and channel outage probability requirements.

[C 105] Resource Allocation for Secure OFDMA Decode-and-Forward Relaying Networks

Derrick Wing Kwan Ng and R. Schober
Conference Papersin Proceedings of the 2011 Canadian Workshop on Information Theory (CWIT 2011), Kelowna, Canada, pp. 202-205, May 2011.

Abstract

In this paper, we formulate an optimization problem for resource allocation and scheduling in orthogonal frequency division multiple access (OFDMA) half-duplex decode-and-forward (DF) relay assisted networks. Our problem formulation takes into account artificial noise generation to combat a multiple antenna eavesdropper. The secrecy data rate, power, and sub-carrier allocation policies are optimized to maximize the average secrecy outage capacity (bit/s/Hz securely delivered to the users via relays). The optimization problem is solved by dual decomposition which results in an efficient iterative algorithm. Simulation results illustrate that the proposed iterative algorithm converges in a small number of iterations and guarantees a non-zero secrecy date rate for a given target secrecy outage probability.

[C 106] Resource Allocation for Secure OFDMA Communication Systems

Derrick Wing Kwan Ng and R. Schober
Conference Papersin Proceedings of the 2011 Australian Communications Theory Workshop (AusCTW), Melbourne, Australia, pp. 13-18, Feb. 2011.

Abstract

In this paper, we formulate an optimization problem for resource allocation and scheduling in orthogonal frequency division multiple access (OFDMA) half-duplex decode-and-forward (DF) relay assisted networks. Our problem formulation takes into account artificial noise generation to combat a multiple antenna eavesdropper. The secrecy data rate, power, and sub-carrier allocation policies are optimized to maximize the average secrecy outage capacity (bit/s/Hz securely delivered to the users via relays). The optimization problem is solved by dual decomposition which results in an efficient iterative algorithm. Simulation results illustrate that the proposed iterative algorithm converges in a small number of iterations and guarantees a non-zero secrecy date rate for a given target secrecy outage probability.

[C 107] Dynamic Resource Allocation in OFDMA Systems with Full and Hybrid-Duplex Relaying

Derrick Wing Kwan Ng and R. Schober
Conference Papersin Proceedings of the IEEE International Conference on Communications (ICC) 2011, Kyoto, Japan, pp. 1-6, Jun. 2011.

Abstract

In this paper, we formulate a joint optimization problem for resource allocation and scheduling in full-duplex orthogonal frequency division multiple access (OFDMA) relaying systems with amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols. Our problem formulation takes into account heterogeneous data rate requirements for delay sensitive users. Besides, a theoretically optimal hybrid relaying, which allows a dynamic selection between AF relaying and DF relaying protocols with full-duplex relays or half-duplex relays, is also considered in the problem formulation and serves as a performance benchmark. A dual decomposition method is employed to solve the resulting optimization problem and a novel distributed iterative resource allocation and scheduling algorithm with closed-form power and subcarrier allocation is derived. Simulation results illustrate that the proposed distributed algorithm requires only a small number of iterations to achieves practically the same performance as the optimal centralized algorithm.

[C 108] Resource Allocation and Scheduling in Multi-Cell OFDMA Decode-and-Forward Relaying Networks

Derrick Wing Kwan Ng and R. Schober
Conference Papersin Proceedings of the IEEE Global Communications Conference (Globecom), Miami, Florida, USA, pp.1-6, Dec. 2010.

Abstract

In this paper, we formulate an optimization problem for resource allocation and scheduling in orthogonal frequency division multiple access (OFDMA) networks. Our problem formulation takes into account artificial noise generation to combat a passive multiple antenna eavesdropper and the effects of imperfect channel state information at the transmitter (CSIT) in slow fading. The optimization problem is solved by dual decomposition which results in an iterative resource allocation algorithm with a fast speed of convergence. The packet data rate, secrecy data rate, power, and subcarrier allocation policies are optimized to maximize the average secrecy outage capacity (bit/s/Hz securely and successfully delivered to the users). Simulation results illustrate that our proposed iterative algorithm converges to the optimal solution in a small number of iterations and guarantees a non-zero secrecy data rate for given target secrecy outage and channel outage probability requirements.

[C 109] Cross-Layer Scheduling for OFDMA Two-way Relay Networks

Derrick Wing Kwan Ng and R. Schober
Conference Papers in Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, pp.1-6, Apr. 2010.

Abstract

In this paper, cross-layer scheduling for orthogonal frequency division multiple access (OFDMA) two-way half-duplex amplify-and-forward (AF) relay assisted networks is studied. Assuming slow fading channels, cross-layer scheduling design with imperfect channel state information at the transmitter (CSIT) and heterogeneous data rate requirements for the users is modeled as an optimization problem, where the rate, power, and subcarrier allocation policies are optimized to maximize the system goodput (bit/s/Hz successfully received). The optimization problem is solved by using dual decomposition and a distributed resource allocation algorithm is derived. Simulation results illustrate that our proposed distributed cross-layer scheduler achieves practically the same performance as the optimal centralized scheduler after a small number of iterations.

[C 110] Cross-Layer Scheduling for OFDMA Amplify-and-Forward Relay Networks

Derrick Wing Kwan Ng and R. Schober
Conference Papers in Proceedings of the IEEE Vehicular Technology Conference (VTC) fall, Anchorage, Alaska, USA, pp. 1-5, Sep. 2009.

Abstract

In this paper, we consider cross-layer scheduling for the downlink of amplify-and-forward (AF) relay-assisted orthogonal frequency-division multiple-access (OFDMA) networks. The proposed cross-layer design takes into account the effects of imperfect channel-state information (CSI) at the transmitter (CSIT) in slow fading. The rate, power, and subcarrier allocation policies are optimized to maximize the system goodput (in bits per second per hertz successfully received by the users). The optimization problem is solved by using dual decomposition, resulting in a highly scalable distributed iterative resource-allocation algorithm. We also investigate the asymptotic performance of the proposed scheduler with respect to (w.r.t.) the numbers of users and relays. We find that the number of relays should grow faster than the number of users to fully exploit the multiuser diversity (MUD) gain. On the other hand, diversity from multiple relays can be exploited to enhance system performance when the MUD gain is saturated due to noise amplification at the AF relays. Furthermore, we introduce a feedback-reduction scheme to reduce the computational burden and the required amount of CSI feedback from the users to the relays. Simulation results confirm the derived analytical results for the growth of the system goodput and illustrate that the proposed distributed cross-layer scheduler only requires a small number of iterations to achieve practically the same performance as the optimal centralized scheduler, even if the information exchanged between the base station (BS) and the relays in each iteration is quantized, and the proposed CSI feedback reduction scheme is employed.

[C 111] Performance Analysis of Outage-Limited Multi-access Cellular Systems with Macro-diversity

Derrick Wing Kwan Ng and V. K. N. Lau
Conference Papers in Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Budapest, Hungary, pp. 1 - 6, Apr. 2009.

Abstract

In this paper, we consider cross-layer scheduling for the downlink of amplify-and-forward (AF) relay-assisted orthogonal frequency-division multiple-access (OFDMA) networks. The proposed cross-layer design takes into account the effects of imperfect channel-state information (CSI) at the transmitter (CSIT) in slow fading. The rate, power, and subcarrier allocation policies are optimized to maximize the system goodput (in bits per second per hertz successfully received by the users). The optimization problem is solved by using dual decomposition, resulting in a highly scalable distributed iterative resource-allocation algorithm. We also investigate the asymptotic performance of the proposed scheduler with respect to (w.r.t.) the numbers of users and relays. We find that the number of relays should grow faster than the number of users to fully exploit the multiuser diversity (MUD) gain. On the other hand, diversity from multiple relays can be exploited to enhance system performance when the MUD gain is saturated due to noise amplification at the AF relays. Furthermore, we introduce a feedback-reduction scheme to reduce the computational burden and the required amount of CSI feedback from the users to the relays. Simulation results confirm the derived analytical results for the growth of the system goodput and illustrate that the proposed distributed cross-layer scheduler only requires a small number of iterations to achieve practically the same performance as the optimal centralized scheduler, even if the information exchanged between the base station (BS) and the relays in each iteration is quantized, and the proposed CSI feedback reduction scheme is employed.

[C 112] Cross-Layer Optimization for OFDMA System with Imperfect CSIT in Quasi Static Channel

V. K. N. Lau, W. K. Ng, David S. W. Hui, and B. Chen
Conference Papers in Proceedings of the International Conference on Communications and Networking in China 2008, pp. 710-715, Aug. 2008.

image Received the Best Paper Award at China Com 2008-Industrial Special Session .

Abstract

Asymptotic performance analysis of orthogonal frequency division multiple access (OFDMA) is conducted in this work. We take a cross-layer approach and analyze how the system performance scale with some important parameters such as number of user, CSIT quality and order of diversity. It is well studied that system goodput scale with number of user K in the order of O(log log K) due to multiuser diversity (system goodput gain) under perfect CSIT assumption. However, in quasi static fading channels with imperfect CSIT, channel outage happens even if capacity achieving coding is applied at the base station. In this case, cross-layer scheduler can protect the packet by increasing the order of diversity (packet outage diversity). So, there is a trade-off between system goodput gain and packet outage diversity.

[C 113] Asymptotic Tradeoff between Cross-Layer Goodput Gain and Outage Diversity in OFDMA Systems with Slow Fading and Delayed CSIT

Derrick Wing Kwan Ng and V. K. N. Lau
Conference Papers in Proceedings of the 2007 IEEE International Symposium on Information Theory (ISIT 2007), Nice, France, pp 2756-2760, Jun. 2007.

Abstract

In this paper, we consider on the asymptotic tradeoff analysis between the system goodput gain and the packet outage diversity gain in cross-layer OFDMA systems with slow frequency selective fading and delayed CSIT. The OFDMA cross-layer design with delayed CSIT is modeled as an optimization problem where the rate adaptation, power adaptation and subcarrier allocation policies are designed to optimize the system goodput (b/s/Hz successfully received by the mobiles). We derived simple closed-form expressions for the power and rate allocations as well as the asymptotic order of growth in system goodput for general CSIT error sigmae 2. We found that the system goodput scales in the order of O(log(1-sigma_e^2/ Nd(log K + Nd log log K))) for large K where Nd is the packet outage diversity and K is the number of user in the cross-layer OFDMA system. Hence, double exponentially larger K is needed to compensate for the penalty in system goodput gain due to CSIT errors sigmae 2 or packet outage diversity Nd for large Nd.

[P 1] Robust Timing Synchronization For MB-OFDM Frequency Hopping Systems In A Sop Environment

Ming Y. Tsang, Chi-Tin Luk, Wing-Kwan Ng , Vincent K. N. Lau, C. Y. Tsui and Roger S. K. Cheng
Patent filed in Sep. 2007, United States Patent Application 20090109953

Abstract

System and methodologies for timing synchronization in a wireless communication system are provided herein. The provided systems and methodologies can utilize various timing synchronization algorithms and an associated state machine to reduce the down time of a wireless communication system due to the presence of simultaneously operating piconets (SOP) and/or other factors. Frequency band finger pattern detection techniques are additionally described that can reduce boundary mismatch rates for wireless receivers. In one example, by making use of the fact that time frequency codes (TFCs) possess unique frequency hopping patterns, system down time can be reduced and OFDM boundary matching can be enhanced to allow a receiver to obtain correct timing information even for communication channels having a very low SINR.

[P 2] SUDAC, User Equipment, Base Station and SUDAC System

Frank Burkhardt, Marco Breiling, Christian Rohde, Wing-Kwan Ng, and Robert Schober
Patent Filed Aug. 27, 2014, EU patent office, Application No./Patent No. 14182528.1-1852

Abstract

[P 3] A Transceiver, a SUDAC, a Method for Signal Processing in a Transceiver, and Methods for Signal Processing in a SUDAC

Frank Burkhardt, Marco Breiling, Christian Rohde, Wing-Kwan Ng, and Robert Schober
Patent Filed Dec. 2014, EU patent office, Application No./Patent No. 14198339.5-1854

Abstract

Energy-Efficient and Secure Communication Systems, (Ph.D. Thesis Exam)

Derrick Wing Kwan Ng
Thesis Ph.D. thesis defense, The University of British Columbia, 2012.

Abstract

Orthogonal frequency division multiple access (OFDMA), multiple--input multiple--output (MIMO), and base station (BS) cooperation are the core techniques for the next generation wireless communication systems. As the communication systems evolve, both service providers and users are demanding not only high data rates, but also energy efficiency and data security. As a result, it is necessary to design novel resource allocation algorithms that meet these new needs. This dissertation develops four resource allocation algorithms which are tailored for different design goals and communication environments. For systems employing the combination of OFDMA and decode-and-forward (DF) relaying technologies, we propose a novel resource allocation algorithm for secure communication. The proposed algorithm takes into account artificial noise generation to combat a passive multiple antenna eavesdropper and the effects of imperfect channel state information at the transmitter (CSIT). Subsequently, we investigate the energy efficiency of OFDMA systems which also provide communication security. We formulate the resource allocation algorithm design as a non-convex optimization problem. By exploiting the properties of fractional programming, the considered non-convex optimization problem is transformed to an equivalent convex optimization problem with a tractable solution, which can be obtained with an iterative algorithm. Thirdly, we study resource allocation for energy efficient communication in OFDMA downlink networks with a large number of transmit antennas. Our proposed resource allocation algorithm takes into account the circuit power consumption, imperfect CSIT, a minimum data rate requirement, and a maximum tolerable channel outage probability. Lastly, we propose a resource allocation algorithm for energy efficient communication in OFDMA downlink networks with cooperative BSs. The resource allocation algorithm design problem is formulated as a non-convex optimization problem which takes into account the circuit power consumption, the limited backhaul capacity, and the minimum required data rate for joint BS zero-forcing beamforming (ZFBF) transmission. By using the concept of perturbation function, we show that the duality gap in the considered system is always zero under some general conditions, despite the non-convexity of the primal problem. Thus, an efficient closed-form power allocation solution for maximization of the energy efficiency of data transmission is derived.

Defense committees: Robert Schober (Thesis supervisor) ,  Vincent W. S. Wong,  Jane Wang, William Welch (Chair), and  Son Vuong.

The Road to 5G Wireless Systems: Resource Allocation for NOMA

Derrick Wing Kwan Ng
Invited Talk Invited Talk, Tsinghua University, Beijing, 2017. (Hosted by Prof. Linglong Dai.)

Abstract

Road to Ubiquitous Communication Networks: Wireless Information and Power Transfer

Derrick Wing Kwan Ng
Invited Talk Invited Talk, Tsinghua University, Beijing, Jan. 2016. (Hosted by Prof. Linglong Dai.)

Abstract

The integration of energy harvesting (EH) capabilities in battery-powered wireless communication devices facilitates self-sustainability of energy limited communication systems. Solar and wind are the major conventional energy sources for EH. However, the availability of these natural energy sources is usually limited by location, climate, and time of day. In theses cases, harvesting from background radio frequency (RF) signals originating from ambient transmitters can support the power needs of the receivers. Unlike the natural energy sources, RF energy is generally weather-independent and can be available on demand. More importantly, RF-based energy harvesting provides the possibility of simultaneous wireless information and power transfer (SWPIT) enabling ubiquitous communication. In this talk, we will first provide a survey on the state-of-the-art wireless power transfer technologies. Next, we will focus on various SWIPT communication systems and discuss the new challenges in designing wireless powered communication networks.

Energy-Efficient and Secure Communication Systems (Ph.D. Departmental Exam)

Derrick Wing Kwan Ng
Thesis Ph.D. departmental exam, The University of British Columbia, Nov. 2011.

Abstract

Orthogonal frequency division multiple access (OFDMA), multiple--input multiple--output (MIMO), and base station (BS) cooperation are the core techniques for the next generation wireless communication systems. As the communication systems evolve, both service providers and users are demanding not only high data rates, but also energy efficiency and data security. As a result, it is necessary to design novel resource allocation algorithms that meet these new needs. This dissertation develops four resource allocation algorithms which are tailored for different design goals and communication environments. For systems employing the combination of OFDMA and decode-and-forward (DF) relaying technologies, we propose a novel resource allocation algorithm for secure communication. The proposed algorithm takes into account artificial noise generation to combat a passive multiple antenna eavesdropper and the effects of imperfect channel state information at the transmitter (CSIT). Subsequently, we investigate the energy efficiency of OFDMA systems which also provide communication security. We formulate the resource allocation algorithm design as a non-convex optimization problem. By exploiting the properties of fractional programming, the considered non-convex optimization problem is transformed to an equivalent convex optimization problem with a tractable solution, which can be obtained with an iterative algorithm. Thirdly, we study resource allocation for energy efficient communication in OFDMA downlink networks with a large number of transmit antennas. Our proposed resource allocation algorithm takes into account the circuit power consumption, imperfect CSIT, a minimum data rate requirement, and a maximum tolerable channel outage probability. Lastly, we propose a resource allocation algorithm for energy efficient communication in OFDMA downlink networks with cooperative BSs. The resource allocation algorithm design problem is formulated as a non-convex optimization problem which takes into account the circuit power consumption, the limited backhaul capacity, and the minimum required data rate for joint BS zero-forcing beamforming (ZFBF) transmission. By using the concept of perturbation function, we show that the duality gap in the considered system is always zero under some general conditions, despite the non-convexity of the primal problem. Thus, an efficient closed-form power allocation solution for maximization of the energy efficiency of data transmission is derived.

Defense committees: Robert Schober (Thesis supervisor) ,  Vikram Krishnamurthy (Chair), Vijay Bhargava, Lutz Lampe,  and Vincent W. S. Wong.

Performance Analysis of the Multi-user System

Derrick Wing Kwan Ng
Thesis Master of Philosophy thesis, The Hong Kong University of Science and Technology, 15th Jul. 2008.

Abstract

Cross-layer design has been shown to offer high spectral efficiency which benefits from the inherent multi-user diversity in wireless fading channels. In cross-layer OFDMA systems with perfect CSIT, it is well known that the system through- put (ergodic capacity) scales in the order of O(log logK) due to the MuDiv gain. However, with imperfect CSIT, it is still not clear whether we can get the same performance as that of the perfect case. In the ?¯rst part of this thesis, we shall consider the cross-layer OFDMA scheduling design under various practical PHY layer and MAC layer constraints for a wireless system with one base station and K mobile users . We study the cross- layer scheduling design with imperfect channel state information (CSI) at the base station for delay-tolerant applications. The imperfectness of CSI is assumed to be the result of feedback or duplexing delay. With imperfect CSI at transmit- ter (CSIT), there exists a potential packet transmission error when the scheduled data rate exceeds the instantaneous channel capacity referring to packet outage. The OFDMA cross-layer design with delayed CSIT is modeled as an mixed integer and convex optimization problem where the rate adaptation, power adaptation and subcarrier allocation policies are designed to optimize the system goodput (b/s/Hz successfully received by the mobiles). At the time same time, we are interested to know the trade-off between packet outage diversity gain and multi-user diversity gain. Therefore, by using extreme value theorem, we are able to show the trade-o?® analytically. In the second part of this thesis, we would like to evaluate the performance of a uplink multiaccess channel with successive interference cancellation receiver equipped in the base-station. We derive analytically the per-user packet outage probability and the total system goodput for multi-access systems using multiuser detector with adaptive successive interference cancellation (MUD-SIC). Slow fad- ing channel is assumed where packet transmission error (outage) is the primary concern even if strong channel coding is applied. To capture the effect of potential packet error, goodput should be used as performance measure. Unlike previous works, our analysis focuses on the error-propagation effects in MUD-SIC detector where the packet outage event for a single user is depending on the other users. Also, we derive the optimal SIC decoding order (to maximize system goodput) and evaluate the closed-form per-user packet outage probabilities for the n users for MUD-SIC. Simulation results are used to verify the analytical expressions.

Defense committees: Vincent K. N. Lau (Thesis supervisor) ,  Roger S. K. Cheng (Chair), and Kam Tim Woo.

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