Uplink Wave-Domain Combiner for Stacked Intelligent Metasurfaces Accounting for Hardware Limitations

TL;DR

This paper analyzes the performance of stacked intelligent metasurfaces (SIMs) in uplink wireless systems, considering hardware limitations, and compares their sum-rate performance to digital phased arrays under various conditions.

Contribution

It introduces a system model that incorporates hardware non-idealities, formulates a sum-rate optimization problem, and evaluates SIMs versus DPAs under realistic channel and hardware constraints.

Findings

SIMs outperform DPAs with equal RF chains

DPAs outperform SIMs with equal aperture size

Hardware limitations significantly impact SIM performance

Abstract

Refractive metasurfaces (RMTSs) offer a promising solution to improve energy efficiency of wireless systems. To address the limitations of single-layer RMTS, stacked intelligent metasurfaces (SIMs), which form the desired precoder and combiner in the wave domain, have been proposed. However, previous analyses overlooked hardware non-idealities that significantly affect SIM performance. In this paper, we study the achievable sum-rate of SIM antennas in an uplink scenario, accounting for hardware constraints. We propose a system model that includes noise and hardware effects, formulate a non-convex sum-rate optimization problem, and solve it using gradient ascent and interior point methods. We compare SIMs and digital phased arrays (DPAs) under Rayleigh fading and 3GPP channels with two conditions: equal number of RF chains and equal physical aperture size. Our results show SIMs outperform DPAs under equal number of RF chains but underperform DPAs with equal aperture size.