Journal
IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS
Volume 20, Issue 5, Pages 3137-3151Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TWC.2020.3047632
Keywords
NOMA; Array signal processing; Downlink; Wireless communication; Resource management; MISO communication; Decoding; Non-orthogonal multiple access; reconfigurable intelligent surface; rate optimization; user fairness; iterative algorithm
Funding
- National Natural Science Foundation of China [61631005, 62071093, U1801261]
- National Key Research and Development Program of China [2018YFB1801105]
- Fundamental Research Funds for the Central Universities [ZYGX2019Z022]
- Programme of Introducing Talents of Discipline to Universities [B20064]
- European Commission [675806]
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Reconfigurable intelligent surface (RIS) is a revolutionary technology for efficient wireless networks, and the paper proposes algorithms to optimize rate performance in an RIS-assisted NOMA system by jointly optimizing transmit beamforming and RIS phase shifts, with efficient algorithms leveraging coordinated descent and SDR techniques. Simulation results show significant rate performance improvement compared to traditional NOMA systems.
Reconfigurable intelligent surface (RIS) is a revolutionary technology to achieve spectrum-, energy-, and cost-efficient wireless networks. This paper considers an RIS-assisted downlink non-orthogonal-multiple-access (NOMA) system. To optimize the rate performance and ensure user fairness, we maximize the minimum decoding signal-to-interference-plus-noise-ratio (equivalently the rate) of all users, by jointly optimizing the (active) transmit beamforming at the base station (BS) and the phase shifts (i.e., passive beamforming) at the RIS. A combined-channel-strength based user-ordering scheme for NOMA decoding is first proposed to decouple the user-ordering design and the joint beamforming design. Efficient algorithms are further proposed to solve the non-convex problem, by leveraging the block coordinated descent and semidefinite relaxation (SDR) techniques. For the single-antenna BS setup, the optimal power allocation at the BS and the asymptotically optimal phase shifts at the RIS are obtained in closed forms. For the multiple-antenna BS setup, it is shown that the rank of the SDR solution of the transmit beamforming design is upper bounded by two. Also, the proposed algorithms are analyzed in terms of convergence and complexity. Simulation results show that the RIS-assisted NOMA system can enhance the rate performance significantly, compared to traditional NOMA without RIS and traditional orthogonal multiple access with/without RIS.
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