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

Abstract

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 singleelement 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.

IRS-Assisted Full Duplex Systems Over Rician and Nakagami Fading Channels

“…Suppose that the channel state information (CSI) over the links related to IRS is perfectly available. In practice, CSI can be acquired by channel estimation technique [23].…”

“…where w i , i ∈ {1, 2}, is the self-interference signal modelled as w i ∼ CN(0, σ 2 wi ). Furthermore, the variance of the SI can be modelled as σ 2 wi = t i P i v i [23], [35], where the range of two parameters is t i > 0 and…”

“…On the other hand, although it is still in its early stages, there are numerous studies presented in order to improve the performance when IRS is utilized in FD wireless networks. Inspired primarily by the reciprocal and non-reciprocal FD models in [23], in this paper we conduct an analysis on the user performance for an IRS-assisted FD network by taking more realistic Rician and Nakagami fadings into account. It is worthy to highlight that IRS-enabled communications are generally characterized by both, a line-of-sight (LoS) and a non-LoS (NLoS) components, rendering the Rician or Nakagami distribution an appropriate candidate for modeling wireless links in IRS systems.…”

On the Secure Performance of Intelligent Reflecting Surface-Assisted HARQ Systems

“…An analysis conducted by Zhang et al further demonstrated the influence of limited phase shifts on achievable performance levels [ 8 ]. Outage probability and spectral efficiency have also been deduced in multiple-element IRS-assisted systems [ 9 ]. In addition, Boulogeorgos et al compared the outage probability and ergodic capacity of IRS-assisted and amplify-and-forward (AF) relaying wireless systems [ 10 ].…”

Joint power and blocklength optimization for RIS‐aided multiple‐access downlink ultra‐reliable low‐latency communication

“…In Refs. [9][10][11][12], RIS-aided systems and relay systems were compared. An RIS requires low-complexity electronic circuits and does not need power amplifiers, mixers, and DACs/ADCs as do relays.…”