Energy Efficiency Optimization of Reconfigurable Intelligent Surfaces with Electromagnetic Field Exposure Constraints

TL;DR

This paper develops algorithms to optimize energy efficiency in RIS-based communication systems while ensuring electromagnetic exposure limits are not exceeded, balancing performance with safety constraints.

Contribution

It introduces two low-complexity algorithms for joint optimization of RIS phase shifts, beamforming, and power, with one guaranteeing global optimality in specific cases.

Findings

RIS can achieve high energy efficiency under exposure constraints

The proposed algorithms are computationally efficient and effective

Exposure constraints can be satisfied without significant performance loss

Abstract

This work considers the problem of energy efficiency maximization in a RIS-based communication link, subject to not only the conventional maximum power constraints, but also additional constraints on the maximum exposure to electromagnetic radiations of the end-users. The RIS phase shifts, the transmit beamforming, the linear receive filter, and the transmit power are jointly optimized, and two provably convergent and low-complexity algorithms are developed. One algorithm can be applied to the general system setups, but does not guarantee global optimality. The second algorithm is provably optimal in a notable special case. The numerical results show that RIS-based communications can ensure high energy efficiency while fulfilling users' exposure constraints to radio frequency emissions.