Cram\'er-Rao Bounds for Holographic Positioning

TL;DR

This paper derives the Cramér-Rao Bound for localizing a source using large antenna arrays in the mmWave range, considering wavefront curvature and source radiation pattern, revealing potential centimeter-level accuracy.

Contribution

It introduces a holographic positioning framework that incorporates wave propagation and source radiation patterns into CRB analysis for large antenna arrays.

Findings

Surfaces of practical size can achieve centimeter-level localization accuracy in mmWave bands.

The radiation pattern and wavefront curvature significantly influence the CRB.

Numerical and asymptotic analyses quantify the impact of system parameters on localization precision.

Abstract

Multiple antennas arrays play a key role in wireless networks for communications but also for localization and sensing applications. The use of large antenna arrays at high carrier frequencies (in the mmWave range) pushes towards a propagation regime in which the wavefront is no longer plane but spherical. This allows to infer the position and orientation of a transmitting source from the received signal without the need of using multiple anchor nodes, located in known positions. To understand the fundamental limits of large antenna arrays for localization, this paper combines wave propagation theory with estimation theory, and computes the Cram\'er-Rao Bound (CRB) for the estimation of the source position on the basis of the three Cartesian components of the electric field, observed over a rectangular surface area. The problem is referred to as holographic positioning and is formulated by taking into account the radiation angular pattern of the transmitting source, which is typically ignored in standard signal processing models. We assume that the source is a Hertzian dipole, and address the holographic positioning problem in both cases, that is, with and without a priori knowledge of its orientation. To simplify the analysis and gain further insights, we also consider the case in which the dipole is located on the line perpendicular to the surface center. Numerical and asymptotic results are given to quantify the CRBs, and to quantify the effect of various system parameters on the ultimate estimation accuracy. It turns out that surfaces of practical size may guarantee a centimeter-level accuracy in the mmWave bands.