How Practical Phase-shift Errors Affect Beamforming of Reconfigurable Intelligent Surface?

TL;DR

This paper investigates how hardware-induced phase-shift errors in reconfigurable intelligent surfaces affect beamforming performance, providing a new model verified by field trials and offering practical design insights.

Contribution

It introduces a new RIS reflection model accounting for phase-shift errors, classifies error types, and analyzes the impact of hardware impairments on beamforming.

Findings

Phase-shift errors significantly degrade beamforming performance.

Different hardware impairments have distinct impacts on RIS effectiveness.

Guidelines for RIS design and deployment are provided for practical systems.

Abstract

Reconfigurable intelligent surface (RIS) is a new technique that is able to manipulate the wireless environment smartly and has been exploited for assisting the wireless communications, especially at high frequency band. However, it suffers from hardware impairments (HWIs) in practical designs, which inevitably degrades its performance and thus limits its full potential. To address this practical issue, we first propose a new RIS reflection model involving phase-shift errors, which is then verified by the measurement results from field trials. With this beamforming model, various phase-shift errors caused by different HWIs can be analyzed. The phase-shift errors are classified into three categories: (1) globally independent and identically distributed errors, (2) grouped independent and identically distributed errors and (3) grouped fixed errors. The impact of typical HWIs, including frequency mismatch, PIN diode failures and panel deformation, on RIS beamforming ability are studied with the theoretical model and are compared with numerical results. The impact of frequency mismatch are discussed separately for narrow-band and wide-band beamforming. Finally, useful insights and guidelines on the RIS design and its deployment are highlighted for practical wireless systems.