Cram\'er-Rao Bound for Direct Position Estimation in OFDM Based Cellular Systems

TL;DR

This paper derives the Cramér-Rao bound for direct position estimation in OFDM cellular systems, demonstrating its superiority over traditional methods in multipath environments and highlighting the importance of bandwidth and multiple symbols for accuracy.

Contribution

It provides the first theoretical CRB analysis for DPE in OFDM systems and benchmarks it against conventional two-step positioning, revealing key factors affecting performance.

Findings

DPE outperforms two-step methods in OFDM systems.

Large bandwidth and increased subcarrier spacing improve accuracy.

Using multiple OFDM symbols enhances localization accuracy.

Abstract

Although direct position estimation (DPE) has been demonstrated to offer enhanced robustness in GNSS receivers, its theoretical limits and performance in OFDM based positioning systems remain largely unexplored. In this paper, the Cram\'er-Rao bound (CRB) for DPE using OFDM based cellular signals is derived and benchmarked against the conventional two-step positioning method to assess their relative performance in non-line-of-sight (NLOS) dominated multipath environments. Numerical results reveal that 1) the DPE method consistently outperforms the two-step approach in OFDM systems under all evaluated conditions; 2) a large bandwidth is crucial in both methods, and increasing subcarrier spacing is more beneficial for a fixed bandwidth; 3) utilizing multiple OFDM symbols for positioning leads to substantial improvements in localization accuracy compared to relying on a single symbol. However, further increasing the number of symbols yields marginal improvements while significantly increasing computational complexity.