Improvement of Bi-directional Communications using Solar Powered Reconfigurable Intelligent Surfaces

TL;DR

This paper proposes a solar-powered reconfigurable intelligent surface framework to enhance bi-directional wireless communication, optimizing power and reflection elements to improve performance even without line-of-sight conditions.

Contribution

It introduces a novel energy-efficient RIS system with an optimization framework for power and element allocation, including solutions for mixed-integer non-linear problems.

Findings

Minimum user rate is maintained without line-of-sight.

Optimization effectively balances energy consumption and communication quality.

Bender decomposition provides near-optimal solutions.

Abstract

Recently, there has been a flurry of research on the use of Reconfigurable Intelligent Surfaces (RIS) in wireless networks to create dynamic radio environments. In this paper, we investigate the use of an RIS panel to improve bi-directional communications. Assuming that the RIS will be located on the facade of a building, we propose to connect it to a solar panel that harvests energy to be used to power the RIS panel's smart controller and reflecting elements. Therefore, we present a novel framework to optimally decide the transmit power of each user and the number of elements that will be used to reflect the signal of any two communicating pair in the system (user-user or base station-user). An optimization problem is formulated to jointly minimize a scalarized function of the energy of the communicating pair and the RIS panel and to find the optimal number of reflecting elements used by each user. Although the formulated problem is a mixed-integer non-linear problem, the optimal solution is found by linearizing the non-linear constraints. Besides, a more efficient close to the optimal solution is found using Bender decomposition. Simulation results show that the proposed model is capable of delivering the minimum rate of each user even if line-of-sight communication is not achievable.