Use of XMTM radio satellite signal as a source of opportunity for passive coherent location

Abstract

This article investigates the use of an XM ™ signal as a source of opportunity for passive coherent location. An analysis of the echo-to-direct signal ratio and the echo-to-noise ratio emphasises two major target detection problems: the masking effect of the direct signal and the low power of the echo from the reflected signal. First, a subspace-based method is proposed to suppress the direct signal by the projection of the received signal in subspaces orthogonal to direct signal. Then, to overcome the problem of low power of the echo, a directive gain technique is also proposed: an overlapped array is used to provide a directive gain while maintaining a sufficient resolution for using the subspaces method. The number of subarrays employed is optimised for maximum gain while avoiding the occurrence of nuls at the output of a filter matched to the direct path signal, for specific numbers of subarrays. The impact of the subtraction of the noise covariance matrix of noise is also studied. The integrated detection system is then tested through simulations to verify its effectiveness for the detection of moving targets.