Double RIS-Assisted MIMO Systems Over Spatially Correlated Rician Fading Channels and Finite Scatterers

TL;DR

This paper explores double RIS-assisted MIMO systems over Rician fading channels with finite scatterers, developing statistical models and proposing beamforming and neural network-based designs to optimize capacity and reliability.

Contribution

It introduces a closed-form statistical analysis of the channels and proposes novel optimization algorithms and neural network frameworks for system enhancement.

Findings

Closed-form statistical channel models derived.

AO-ADMM algorithm effectively optimizes capacity.

Neural networks improve symbol error rate performance.

Abstract

This paper investigates double RIS-assisted MIMO communication systems over Rician fading channels with finite scatterers, spatial correlation, and the existence of a double-scattering link between the transceiver. First, the statistical information is driven in closed form for the aggregated channels, unveiling various influences of the system and environment on the average channel power gains. Next, we study two active and passive beamforming designs corresponding to two objectives. The first problem maximizes channel capacity by jointly optimizing the active precoding and combining matrices at the transceivers and passive beamforming at the double RISs subject to the transmitting power constraint. In order to tackle the inherently non-convex issue, we propose an efficient alternating optimization algorithm (AO) based on the alternating direction method of multipliers (ADMM). The second problem enhances communication reliability by jointly training the encoder and decoder at the transceivers and the phase shifters at the RISs. Each neural network representing a system entity in an end-to-end learning framework is proposed to minimize the symbol error rate of the detected symbols by controlling the transceiver and the RISs phase shifts. Numerical results verify our analysis and demonstrate the superior improvements of phase shift designs to boost system performance.