Filter by type:

Sort by year and type:

[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.

[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

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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

[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.

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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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

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

[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

[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

[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

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

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.

[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.

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.

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.

[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.

[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.

[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.

[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.

[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

[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.

[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.

<

[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.

[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.

[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

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.

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.

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.

[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.

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.

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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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

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)

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

[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

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,

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

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

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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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:

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

[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.

[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.

[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.

[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

[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.

[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.

[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

[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

[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

[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

[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

[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

[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

[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

[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

[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

[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

[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

[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

[C 36] Optimal Beamforming for Multiuser Secure SWIPT Systems

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

Received the Best Paper Award .

[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

[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.

Received the Best Paper Award .

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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

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

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

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.

[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.

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 proÃ¯Â¬?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 Ã¯Â¬?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.

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.

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.

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

[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

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.)

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 ?Â¯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?Â® 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.

Disclaimer: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.

IEEE material: Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.