IRS-Aided Overloaded Multi-Antenna Systems: Joint User Grouping and Resource Allocation

• Published in: IEEE transactions on wireless communications Vol. 23; no. 8; pp. 8297 - 8313
• Main Authors: Gao, Ying, Wu, Qingqing, Chen, Wen, Liu, Yang, Li, Ming, Costa, Daniel Benevides da
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Antennas; Beamforming; Constraints; Convexity; Energy harvesting; Errors; Intelligent reflecting surface; Interference; Minimax techniques; MISO communication; Mixed integer; Multiplexing; Optimization; overloaded multi-antenna systems; Overloading; phase errors; Power transfer; Reconfigurable intelligent surfaces; Resource allocation; Robust design; Simultaneous wireless information and power transfer; SWIPT; Throughput; Transmitting antennas; user grouping; Wireless communication
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2023.3348292

This paper studies an intelligent reflecting surface (IRS)-aided multi-antenna simultaneous wireless information and power transfer (SWIPT) system where an <inline-formula> <tex-math notation="LaTeX">M </tex-math></inline-formula>-antenna access point (AP) serves <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula> single-antenna information users (IUs) and <inline-formula> <tex-math notation="LaTeX">J </tex-math></inline-formula> single-antenna energy users (EUs) with the aid of an IRS with phase errors. We explicitly concentrate on overloaded scenarios where <inline-formula> <tex-math notation="LaTeX">K + J > M </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">K \geq M </tex-math></inline-formula>. Our goal is to maximize the minimum throughput among all the IUs by optimizing the allocation of resources (including time, transmit beamforming at the AP, and reflect beamforming at the IRS), while guaranteeing the minimum amount of harvested energy at each EU. Towards this goal, we propose two user grouping (UG) schemes, namely, the non-overlapping UG scheme and the overlapping UG scheme, where the difference lies in whether identical IUs can exist in multiple groups. Different IU groups are served in orthogonal time dimensions, while the IUs in the same group are served simultaneously with all the EUs via spatial multiplexing. The two problems corresponding to the two UG schemes are mixed-integer non-convex optimization problems and difficult to solve optimally. We first provide a method to check the feasibility of these two problems, and then propose efficient algorithms for them based on the big-M formulation, the penalty method, the block coordinate descent, and the successive convex approximation. Simulation results show that: 1) the non-robust counterparts of the proposed robust designs are unsuitable for practical IRS-aided SWIPT systems with phase errors since the energy harvesting constraints cannot be satisfied; 2) the proposed UG strategies can significantly improve the max-min throughput over the benchmark schemes without UG or adopting random UG; 3) the overlapping UG scheme performs much better than its non-overlapping counterpart when the absolute difference between <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">M </tex-math></inline-formula> is small and the EH constraints are not stringent.