Spatial Equalization Before Reception: Reconfigurable Intelligent Surfaces for Multi-path Mitigation

TL;DR

This paper introduces a novel use of reconfigurable intelligent surfaces (RISs) as spatial equalizers to mitigate multi-path fading in wireless systems, enabling equalization during transmission and reducing inter-symbol interference.

Contribution

The paper proposes a new RIS-based spatial equalization method that operates during transmission, differing from traditional beamforming approaches, with an iterative algorithm for phase shift optimization.

Findings

Effectively eliminates multi-path fading in simulations.

Reduces inter-symbol interference compared to benchmarks.

Demonstrates practical feasibility of RIS-based equalization.

Abstract

Reconfigurable intelligent surfaces (RISs), which enable tunable anomalous reflection, have appeared as a promising method to enhance wireless systems. In this paper, we propose to use an RIS as a spatial equalizer to address the well-known multi-path fading phenomenon. By introducing some controllable paths artificially against the multi-path fading through the RIS, we can perform equalization during the transmission process instead of at the receiver, and thus all the users can share the same equalizer. Unlike the beamforming application of the RIS, which aims to maximize the received energy at receivers, the objective of the equalization application is to reduce the inter-symbol interference (ISI), which makes phase shifts at the RIS different. To this end, we formulate the phase shift optimization problem and propose an iterative algorithm to solve it. Simulation results show that the multi-path fading effect can be eliminated effectively compared to benchmark schemes.