Multi-LEO-Assisted Terrestrial Multistatic ISAC for 3-D Target Localisation with CRLB Analysis

Abstract

Low Earth orbit (LEO) satellites provide elevated and spatially diverse viewpoints for enhancing three-dimensional (3-D) sensing in integrated satellite-terrestrial networks. This paper investigates a LEO-assisted terrestrial multistatic integrated sensing and communication (ISAC) network for 3-D target localisation, where multiple LEO satellites act as cooperative sensing illuminators and provide additional bistatic observations to distributed terrestrial radar receivers. However, reliable 3-D localisation remains challenging because the achievable accuracy is strongly affected by weak satellite-assisted echoes and bistatic sensing geometry, which motivates the CRLB analysis to benchmark the fundamental localisation limit and guide receiver deployment. Based on the combined terrestrial and satellite-assisted bistatic observations, a 3-D localisation framework is developed, together with a channel-weighted Fisher information matrix (FIM) and a closed-form Cram#x00E9;r-Rao lower bound (CRLB) approximation. Numerical simulations evaluate the average signalto-clutter-plus-noise ratio (SCNR), 3-D localisation root-meansquare error (RMSE) and 3-D root-CRLB under different sensing geometries and receiver deployments. The results show that LEOassisted bistatic observations improve the average SCNR and 3-D localisation accuracy, especially for enlarged sensing regions and elevated UAV targets.