Energy-Efficient Wireless Communications with Distributed Reconfigurable Intelligent Surfaces

TL;DR

This paper proposes energy-efficient resource allocation strategies for wireless networks with distributed reconfigurable intelligent surfaces, optimizing RIS control and beamforming to significantly improve energy efficiency.

Contribution

It introduces novel iterative algorithms for joint optimization of RIS on-off status and reflection coefficients, enhancing energy efficiency in multi-user wireless systems.

Findings

Achieves up to 33% energy efficiency gains in single-user scenarios.

Achieves up to 68% energy efficiency gains in multi-user scenarios.

Proposes low-complexity algorithms suitable for practical deployment.

Abstract

This paper investigates the problem of resource allocation for a wireless communication network with distributed reconfigurable intelligent surfaces (RISs). In this network, multiple RISs are spatially distributed to serve wireless users and the energy efficiency of the network is maximized by dynamically controlling the on-off status of each RIS as well as optimizing the reflection coefficients matrix of the RISs. This problem is posed as a joint optimization problem of transmit beamforming and RIS control, whose goal is to maximize the energy efficiency under minimum rate constraints of the users. To solve this problem, two iterative algorithms are proposed for the single-user case and multi-user case. For the single-user case, the phase optimization problem is solved by using a successive convex approximation method, which admits a closed-form solution at each step. Moreover, the optimal RIS on-off status is obtained by using the dual method. For the multi-user case, a low-complexity greedy searching method is proposed to solve the RIS on-off optimization problem. Simulation results show that the proposed scheme achieves up to 33\% and 68\% gains in terms of the energy efficiency in both single-user and multi-user cases compared to the conventional RIS scheme and amplify-and-forward relay scheme, respectively.