Reconfigurable Intelligent Surface Assisted OFDM Relaying: Subcarrier Matching With Balanced SNR

• Published in: IEEE transactions on vehicular technology Vol. 72; no. 2; pp. 2216 - 2230
• Main Authors: Zhang, Tong, Wang, Shuai, Zhuang, Yufan, You, Changsheng, Wen, Miaowen, Wu, Yik-Chung
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Array signal processing; Beamforming; Decode-and-forward relay; Machine learning; Matching; Microbalances; Mixed integer; Nonlinear programming; OFDM; Optimization; Orthogonal Frequency Division Multiplexing; passive beamforming; Reconfigurable intelligent surfaces; Relaying; Relays; RIS; Signal to noise ratio; Simulation; subcarrier matching; Subcarriers; Time-domain analysis; Time-frequency analysis
• ISSN: 0018-9545; 1939-9359
• DOI: 10.1109/TVT.2022.3213368

This paper considers a reconfigurable intelligent surface (RIS) aided orthogonal frequency division multiplexing (OFDM) relaying system, and investigates the joint design of RIS passive beamforming and subcarrier matching under two cases, where Case-I ignores the source-RIS-destination signal, while Case-II explores this signal for rate enhancement. We formulate a mixed-integer nonlinear programming (MINIP) problem to maximize the sum achievable rate of all subcarriers by jointly optimizing the passive beamforming and subcarrier matching. To solve this problem, we first develop a branch-and-bound (BnB)-based alternating optimization algorithm for attaining a near-optimal solution. Then, a low-complexity difference-of-convex penalty-based algorithm and learning-to-optimize approach are also proposed. Finally, simulation results demonstrate that the RIS-assisted OFDM relaying system achieves a substantial achievable rate gain as compared to that without RIS since RIS recasts the subcarrier matching and balances the signal-to-noise ratio (SNR) among different subcarrier pairs.