RIS-Aided Localization under Position and Orientation Offsets in the Near and Far Field

TL;DR

This paper provides a Bayesian analysis of RIS-assisted localization considering position and orientation offsets in near and far fields, highlighting the impact of phase offsets and antenna configurations on localization accuracy.

Contribution

It introduces a comprehensive Bayesian framework for analyzing RIS-assisted localization under offsets and phase uncertainties in both near and far field regimes.

Findings

RIS orientation offset affects pathloss when element spacing is half wavelength

Unknown phase offset hinders RIS orientation estimation in far-field

Near-field observations enable RIS orientation estimation with multiple receive antennas

Abstract

This paper presents a rigorous Bayesian analysis of the information in the signal (consisting of both the line-of-sight (LOS) path and reflections from multiple reconfigurable intelligent surfaces (RISs)) that originate from a single base station (BS) and is received by a user equipment (UE). For a comprehensive Bayesian analysis, both near and far field regimes are considered. The Bayesian analysis views both the location of the RISs and previous information about the UE as {\em a priori} information for UE localization. With outdated {\em a priori} information, the position and orientation offsets of the RISs become parameters that need to be estimated and fed back to the BS for correction. We first show that when the RIS elements have a half wavelength spacing, this RIS orientation offset is a factor in the pathloss of the RIS paths. Subsequently, we show through the Bayesian equivalent Fisher information matrix (EFIM) for the channel parameters that the RIS orientation offset cannot be corrected when there is an unknown phase offset in the received signal in the far-field regime. However, the corresponding EFIM for the channel parameters in the received signal observed in the near-field shows that this unknown phase offset does not hinder the estimation of the RIS orientation offset when the UE has more than one receive antenna. Furthermore, we use the EFIM for the UE location parameters to present bounds for UE localization in the presence of RIS uncertainty.