Distributed MIMO Positioning: Fundamental Limit Analysis and User Tracking Framework Design

TL;DR

This paper analyzes the fundamental limits of 3D positioning in distributed MIMO systems using a realistic polarimetric antenna model, and proposes a tracking framework that achieves centimeter-level accuracy with optimized AP management.

Contribution

It introduces a polarimetric model for realistic antenna patterns, derives the fundamental positioning limits via FIM, and develops a PEB-aware tracking framework with AP management for efficient, high-precision user tracking.

Findings

Achieves centimeter-level tracking accuracy in real-world measurements.

PEB-aware AP management reduces system overhead while maintaining performance.

Fundamental limits are characterized by a weighted sum of AP-UE pair contributions.

Abstract

This paper presents a comprehensive study on the 3D positioning capabilities in distributed multiple-input multiple-output (MIMO) systems. Unlike previous studies that mainly rely on idealized isotropic antenna models, we adopt a polarimetric model that takes advantage of effective aperture distribution functions to characterize realistic antenna patterns, placements, and polarization effects. Based on this model, we analyze the fundamental limits of UE positioning using the Fisher information matrix (FIM) and the position error bound (PEB). The FIM is shown to be expressed as a weighted sum of the information contributions from individual access point (AP)-UE pairs, with each contribution interpreted geometrically across distance, azimuth, and elevation dimensions. The impact of the UE tilt and the spatial distribution of APs on the PEBs is further analyzed. As a further advancement, we propose a complete positioning framework from a UE tracking perspective. By integrating a global probability hypothesis density filter and a PEB-aware AP management strategy, the framework enables accurate tracking while optimizing AP scheduling. Finally, we present a distributed MIMO channel measurement campaign to validate the proposed framework. The results demonstrate a centimeter-level tracking accuracy. In addition, the PEB-aware AP management strategy is shown to maintain robust tracking performance while significantly reducing the number of concurrently active APs, thus lowering the overall system overhead.