Range-Free Localisation for Monostatic Passive Radar Employing Multi-Narrowband Illuminators

Abstract

Passive localisation with narrowband external illuminators is attractive for low-cost and flexible deployment, yet accurate positioning becomes difficult when time-delay (range) information is unreliable or unavailable. To address this limitation and leverage signals from multi-illuminator, this paper investigates range-free 3-D localisation for a monostatic passive radar. Doppler and DOA measurements (and, when available, Doppler-rate) are incorporated into a maximum-likelihood framework for joint position–velocity estimation. To mitigate the resulting high-dimensional optimisation, we propose an iteration based velocity estimation that expresses the velocity estimate as a function of a candidate position, reducing the original 6-D problem to a 3-D position search. A Gauss–Newton (GN) guided dimension-reduced Particle Swarm Optimisation (PSO) is then employed to accelerate convergence by steering elite particles along local GN directions while preserving global exploration. Simulation and measured-data results demonstrate that the proposed method achieves close to the Cramér-Rao Lower Bound (CRLB) accuracy with significantly improved efficiency, enabling stable localisation with fewer observations in both single-illuminator and multi-illuminator configurations.