Reconfigurable Intelligent Surface assisted Two–Way Communications: Performance Analysis and Optimization

Abstract

<jats:p>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 $\left(\log(\rho)/\rho\right)^L$ rate where $L$ is the number of elements, whereas the spectral efficiency increases at $\log(\rho)$ rate at large average SINR $\rho$. 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.</jats:p>

Smart Radio Environments Empowered by Reconfigurable Intelligent Surfaces: How It Works, State of Research, and The Road Ahead

“…In [175], the authors consider a wireless system in which two-way communications take place between a pair of users, with the help of an RIS. Reciprocal and non-reciprocal channels are considered, and the RIS phase shifts are optimized in order to maximize the SINR at the two receivers.…”

Average Rate and Error Probability Analysis in Short Packet Communications Over RIS-Aided URLLC Systems

“…Note that the analysis is performed over infinite blocklength regime without the presence of the direct channel. Furthermore, the authors in [28] approximated the composite channel reflected from the RIS as a Gamma RV by Kullback-Leibler (KL) divergence method. The asymptotic analysis of outage probability for reciprocal and non-reciprocal scenarios in a two-way communication system is elaborated.…”

“…where to arrive in a lower-bound we should elaborate the righthand of (28). To continue, we apply Taylor series expansion of 1 γ then, take average from both sides which yields…”

Performance Analysis of RIS-Aided Systems With Practical Phase Shift and Amplitude Response

“…In [17], the outage probability (OP) was computed and minimized by optimizing the phase shifts of an RIS over Rician fading channels. In [18], an RIS was considered for assisting the communication between two users, and the OP and spectral efficiency were studied by using a Gamma approximation over Rayleigh fading channels. In [19], exact expressions of the OP and EC for an RIS-assisted system over Fox's H fading channels were provided.…”