Frugal RIS-aided 3D Localization with CFO under LoS and NLoS Conditions

TL;DR

This paper presents a frugal RIS-assisted 3D localization and synchronization method for minimal-resource 6G scenarios, effective under LoS and NLoS conditions with CFO and multi-path interference.

Contribution

It introduces novel low-resource algorithms for RIS-aided 3D localization and CFO estimation, validated against theoretical bounds and tested under diverse practical conditions.

Findings

Algorithms achieve near-CRB accuracy in simulations

Effective under both LoS and NLoS conditions

Robust to CFO variations and multi-path interference

Abstract

In this paper, we investigate 3-D localization and frequency synchronization with multiple reconfigurable intelligent surfaces (RISs) in the presence of carrier frequency offset (CFO) for a stationary user equipment (UE). In line with the 6G goals of sustainability and efficiency, we focus on a frugal communication scenario with minimal spatial and spectral resources (i.e., narrowband single-input single-ouput system), considering both the presence and blockage of the line-of-sight (LoS) path between the base station (BS) and the UE. We design a generalized likelihood ratio test (GLRT)-based LoS detector, channel parameter estimation and localization algorithms, with varying complexity. To verify the efficiency of our estimators, we compare the root mean-squared error (RMSE) to the Cram\'er- Rao bound (CRB) of the unknown parameters. We also evaluate the sensitivity of our algorithms to the presence of uncontrolled multi-path components (MPC) and various levels of CFO. Simulation results showcase the effectiveness of the proposed algorithms under minimal hardware and spectral requirements, and a wide range of operating conditions, thereby confirming the viability of RIS-aided frugal localization in 6G scenarios.