Phase Dependent Loss Analysis for RIS Systems

TL;DR

This paper analyzes how phase dependent loss (PDL) affects the signal-to-noise ratio in RIS-assisted wireless links, providing a closed-form expression for mean SNR considering PDL effects.

Contribution

It derives a closed-form expression for the mean SNR in RIS systems accounting for phase dependent loss, supported by circuit-based attenuation modeling.

Findings

PDL significantly reduces the mean SNR in RIS systems.

The derived expression accurately predicts the impact of PDL as validated by numerical results.

Optimal RIS design without PDL is suboptimal when PDL is present.

Abstract

In this paper we focus on phase dependent loss (PDL), an important aspect of reconfigurable intelligent surfaces (RIS) where the signals reflected from the RIS elements are attenuated by varying amounts depending on the phase rotation provided by the element. To evaluate the effects of PDL, we analyse the SNR of a SIMO RIS-aided wireless link. We assume that the channel between the base station (BS) and RIS is a rank-1 LOS channel while the user (UE)-BS and UE-RIS are correlated Rayleigh channels. The RIS design is optimal in the absence of PDL and maximizes the SNR in this scenario. Specifically, we derive a closed form expression for the mean SNR in the presence of PDL. The attenuation function used for PDL was developed from a detailed circuit analysis of RIS elements. Leveraging the derived results, we analytically characterise the impact of PDL on the mean SNR. Numerical results are conducted to validate the derived expressions and verify the analysis.