On the Sensitivity of Active RIS Systems to CSI Errors: Joint Optimization and Performance Trade-off

TL;DR

This paper investigates the impact of CSI errors on active RIS systems in multi-user uplink scenarios, proposing joint optimization methods to maximize sum-rate despite imperfect channel information.

Contribution

It introduces a joint optimization framework for active RIS-assisted systems considering CSI errors and analyzes the performance trade-offs involved.

Findings

Active RIS is more sensitive to CSI errors than passive RIS at high error variances.

Iterative optimization methods effectively address the non-convex sum-rate maximization problem.

Numerical results demonstrate the impact of CSI imperfections on system performance.

Abstract

In this paper, the problem of maximizing the sum-rate is addressed for a multi-user uplink scenario that is assisted by an active reconfigurable intelligent surface (RIS). The maximization is achieved by optimizing the beamforming at the base station, the users' transmit power, active RIS elements phase shifts, and active gains in presence of imperfect channel state information (CSI). The non-convex maximization problem is decomposed into sub-problems and solved via iterative approaches including the Lagrangian method, the projected gradient descent, multi-variate Taylor expansion and fractional programming. Numerical results show that the active RIS is more sensitive to CSI imperfections than passive one at high error variances.