Using Reconfigurable Intelligent Surfaces for UE Positioning in mmWave MIMO Systems

TL;DR

This paper introduces a RIS-assisted framework for accurate UE positioning in mmWave MIMO systems, effectively handling scenarios with blocked LOS paths by leveraging reflection paths and optimizing RIS phase shifts.

Contribution

The paper develops a novel RIS-aided positioning method, including a low-complexity estimator and phase shift optimization, extending to multiple BSs and UEs, and derives the CRB for performance benchmarking.

Findings

The proposed method approaches the CRB in accuracy.

RIS phase shift optimization improves positioning precision.

The framework effectively localizes UEs even with LOS blockage.

Abstract

A reconfigurable intelligent surface (RIS) consists of massive meta elements, which results in a reflection path between a base station (BS) and user equipment (UE). In wireless localization, this reflection path aids in positioning accuracy, especially when the line-of-sight (LOS) path is subject to severe blockage and fading. We develop a RIS-aided positioning framework to locate a UE in environments where the LOS path may or may not be available. We first estimate the RIS-aided channel parameters from the received signals at the UE. To reduce algorithmic complexity, we propose a linear combination of the estimated UE positions from the direct and reflection paths, which is shown to be approximately the maximum likelihood estimator under the large-sample regime when the estimates from different paths are independent. We optimize the RIS phase shifts to improve the positioning accuracy, and extend the proposed approach to the case with multiple BSs and UEs. We derive the Cramer-Rao bound (CRB) and demonstrate numerically that our proposed method approaches the CRB.