Optimization for full-duplex emergency communication enhanced by Beyond-diagonal RIS

Abstract

In post-disaster scenarios, there are high demands for the convenience, flexibility, and energy efficiency of emergency communication setup. Beyond-diagonal (BD) RIS presents benefits including passivity, ease of deployment, and cost-effectiveness, while also providing a significant performance improvement over conventional RIS. This paper investigates the potential of a BD-RIS-aided full-duplex (FD) system to enhance communication quality and spectral efficiency in post-disaster scenarios, where the BD-RIS is deployed to establish reflective links with users in blind zones. Firstly, we aim to maximize the weighted sum of downlink and uplink rates by jointly designing the transmit precoder of temporary base station and the phase shift matrix of BD-RIS, while satisfying the transmit power, symmetry and orthogonality constraints. Then, to address this non-convex problem, we reformulate the original problem as a weighted sum of mean squared error minimization problem and employ the alternating optimization algorithm as well as the alternating direction method of multipliers to solve this equivalent minimization problem. Finally, simulation results demonstrate that the proposed scheme achieves a superior weighted sum of downlink and uplink rates compared to a baseline schemes. Additionally, deploying a BD-RIS may also reduce the transmit energy expenditure of users.