Multiple-Object Positioning in N-LOS RIS-Aided Environment: Using a Single-Element Antenna

Abstract

Estimating the direction of arrival (DOA) of signals from radio frequency (RF) scattering objects and determining their location in the absence of a line-of-sight (LOS) channel is a significant challenge in sensing and wireless communication systems. This paper presents a narrowband measurement method that employs a single-element receive antenna and reconfigurable intelligent surfaces (RIS) to overcome this issue. By utilizing low-cost passive elements that reflect signals with varying phase shifts over consecutive snapshots, RIS generates the necessary linearly independent signal components for subspace-based algorithms. We also propose a novel DOA-based localization algorithm for multi-object scenarios using three RISs and a single-element receiver. Additionally, a method is introduced to mitigate interference from wireless channels that do not interact with the RIS. To evaluate parameter estimation accuracy, we derive the Cramér-Rao lower bound (CRLB) for both DOA estimation and localization problems. Numerical results show that the mean square error (MSE) of the proposed DOA estimation algorithm approaches the CRLB as the signal-to-noise ratio (SNR) increases, and the localization algorithm delivers strong accuracy in a moderate SNR regime.