Reconfigurable intelligent surface assisted two–way communications: Performance analysis and optimization

作     者：Atapattu, Saman Fan, Rongfei Dharmawansa, Prathapasinghe Wang, Gongpu Evans, Jamie Tsiftsis, Theodoros A. 

作者机构：The Department of Electrical and Electronic Engineering The University of Melbourne VIC Australia The School of Information and Electronics Beijing Institute of Technology Beijing100081 China Department of Electronic and Telecommunications Engineering University of Moratuwa Moratuwa Sri Lanka The School of Computer and Information Technology Beijing Jiaotong University Beijing100044 China The Institute of Physical Internet and the School of Intelligent Systems Science and Engineering Jinan University Zhuhai519070 China 

出 版 物：《TechRxiv》 (TechRxiv)

年 卷 期：2020年

核心收录：

主　　题：Signal to noise ratio 

摘      要：In this paper, we investigate the two-way communication between two users assisted by a re-configurable intelligent surface (RIS). The scheme that two users communicate simultaneously in the same time slot over Rayleigh fading channels is considered. The channels between the two users and RIS can either be reciprocal or non-reciprocal. For reciprocal channels, we determine the optimal phases at the RIS to maximize the signal-to-interference-plus-noise ratio (SINR). We then derive exact closed-form expressions for the outage probability and spectral efficiency for single-element RIS. By capitalizing the insights obtained from the single-element analysis, we introduce a gamma approximation to model the product of Rayleigh random variables which is useful for the evaluation of the performance metrics in multiple-element RIS. Asymptotic analysis shows that the outage decreases at (log(ρ)/ρ)L rate where L is the number of elements, whereas the spectral efficiency increases at log(ρ) rate at large average SINR ρ. For non-reciprocal channels, the minimum user SINR is targeted to be maximized. For single-element RIS, closed-form solutions are derived whereas for multiple-element RIS the problem turns out to be non-convex. The latter is relaxed to be a semidefinite programming problem, whose optimal solution is achievable and serves as a sub-optimal solution. © 2020, CC BY.