Optimizing the Achievable Rate in MIMO Systems Assisted by Multiple Reconfigurable Intelligent Surfaces

TL;DR

This paper proposes an iterative optimization algorithm for jointly designing transmit precoders and multiple RIS phases in MIMO systems, significantly enhancing achievable data rates in smart wireless environments.

Contribution

It introduces a novel joint optimization method using mAPG for multiple RIS-assisted MIMO systems, with proven convergence and superior performance over benchmarks.

Findings

The proposed algorithm achieves higher data rates than benchmark schemes.

Simulation results confirm the effectiveness of the joint design approach.

The method converges reliably with a detailed convergence analysis.

Abstract

In recent years there has been a growing interest in reconfigurable intelligent surfaces (RISs) as enablers for the realization of smart radio propagation environments which can provide performance improvements with low energy consumption in future wireless networks. However, to reap the potential gains of RIS it is crucial to jointly design both the transmit precoder and the phases of the RIS elements. Within this context, in this paper we study the use of multiple RIS panels in a parallel or multi-hop configuration with the aim of assisting a multi-stream multiple-input multiple-output (MIMO) communication. To solve the nonconvex joint optimization problem of the precoder and RIS elements targeted at maximizing the achievable rate, we propose an iterative algorithm based on the monotone accelerated proximal gradient (mAPG) method which includes an extrapolation step for improving the convergence speed and monitoring variables for ensuring sufficient descent of the algorithm. Based on the sufficient descent property we then present a detailed convergence analysis of the algorithm which includes expressions for the step size. Simulation results in different scenarios show that, besides being effective, the proposed approach can often achieve higher rates than other benchmarked schemes.