[论文解读] Reconfigurable Intelligent Surface (RIS) Aided Multi-User Networks: Interplay Between NOMA and RIS

Yuanwei Liu, Xidong Mu+4 more|arXiv (Cornell University)|Nov 26, 2020

Advanced Wireless Communication Technologies参考文献 15被引用 34

一句话总结

该论文分析在NOMA与OMA下的RIS辅助多用户网络，表明动态RIS配置对NOMA是容量达成的，考察RIS部署，并提出RIS-NOMA系统的联合波束成形设计。

ABSTRACT

This article focuses on the exploitation of reconfigurable intelligent surfaces (RISs) in multi-user networks employing orthogonal multiple access (OMA) or non-orthogonal multiple access (NOMA), with an emphasis on investigating the interplay between NOMA and RIS. Depending on whether the RIS reflection coefficients can be adjusted only once or multiple times during one transmission, we distinguish between static and dynamic RIS configurations. In particular, the capacity region of RIS aided single-antenna NOMA networks is characterized and compared with the OMA rate region from an information-theoretic perspective, revealing that the dynamic RIS configuration is capacity-achieving. Then, the impact of the RIS deployment location on the performance of different multiple access schemes is investigated, which reveals that asymmetric and symmetric deployment strategies are preferable for NOMA and OMA, respectively. Furthermore, for RIS aided multiple-antenna NOMA networks, three novel joint active and passive beamformer designs are proposed based on both beamformer based and cluster based strategies. Finally, open research problems for RIS-NOMA networks are highlighted.

研究动机与目标

• Motivate and study RIS-aided multi-user networks with MA schemes (NOMA and OMA).
• Characterize information-theoretic capacity limits under static and dynamic RIS configurations.
• Explore RIS deployment strategies and their impact on NOMA and OMA performance.
• Propose joint active and passive beamforming designs for RIS-aided multi-antenna NOMA networks.
• Highlight open research problems and future directions in RIS-NOMA systems.

提出的方法

• Model the RIS-aided multi-user broadcast channel with a single-antenna BS and multiple single-antenna users assisted by an RIS.
• Distinguish static RIS configuration (one-time reflection coefficients) from dynamic RIS configuration (reflection coefficients updated multiple times during one transmission).
• Derive capacity regions for RIS-aided BC under static and dynamic RIS configurations, showing dynamic RIS with NOMA is capacity-achieving.
• Propose deployment strategies for RIS (consolidation vs reverse) and analyze their impact on NOMA and OMA.
• Develop joint active and passive beamforming designs for RIS-aided multi-antenna NOMA networks, including beamformer-based and cluster-based approaches.

实验结果

研究问题

• RQ1 What are the fundamental capacity limits of RIS-aided multi-user networks under NOMA and OMA with static versus dynamic RIS configurations?
• RQ2 How does RIS deployment location affect performance of NOMA and OMA in RIS-aided networks?
• RQ3 What joint active and passive beamforming strategies can effectively exploit RIS in multi-antenna NOMA networks?
• RQ4 What are practical tradeoffs between complexity and capacity when using dynamic RIS configurations and SIC in NOMA?
• RQ5 What open challenges remain for RIS-NOMA networks regarding CSI, ML design, and hardware verification?

主要发现

• Dynamic RIS configuration is capacity-achieving for RIS-aided multi-user BC with NOMA, outperforming static RIS and OMA in capacity regions.
• Dynamic RIS provides larger gains for OMA than for NOMA in certain scenarios, highlighting a capacity-complexity tradeoff.
• Asymmetric RIS deployment (closer to one user) benefits NOMA by increasing channel disparity, while symmetric deployment favors FDMA/TDMA.
• For multiple-antenna NOMA, equivalent reconfigurable channel design helps joint optimization of active and passive beamformers.
• Cluster-based RIS-NOMA designs (centralized and distributed) offer different coverage and CSI requirements, with tradeoffs in complexity and scalability.