Two-Timescale Transmission Design for Wireless Communication Systems Aided by Active RIS

TL;DR

This paper proposes a two-timescale transmission design for active RIS-assisted wireless systems, optimizing phase shifts to improve achievable rate while reducing channel estimation overhead, and demonstrates active RIS's superior performance over passive RIS.

Contribution

It introduces a novel two-timescale channel estimation approach and derives a closed-form expression for achievable rate in active RIS systems, enhancing system performance.

Findings

Active RIS achieves higher achievable rate than passive RIS.

Two-timescale CSI reduces estimation and feedback overhead.

Optimized phase shifts improve system throughput.

Abstract

This paper considers an active reconfigurable intelligent surface (RIS)-aided communication system, where an M-antenna base station (BS) transmits data symbols to a single-antenna user via an N-element active RIS. We use two-timescale channel state information (CSI) in our system, so that the channel estimation overhead and feedback overhead can be decreased dramatically. A closed-form approximate expression of the achievable rate (AR) is derived and the phase shift at the active RIS is optimized. In addition, we compare the performance of the active RIS system with that of the passive RIS system. The conclusion shows that the active RIS system achieves a lager AR than the passive RIS system.