Passive Covert Radars using CP-OFDM SFN. Reference signal recovery from blind beamforming

A passive Coherent Location (PCL) system uses the signal transmitted by so called illuminators-of-opportunity in the environment for the illumination of targets. It is then necessary to recover the original transmitted signal to be compared to the targets echoes. With CP-OFDM transmissions, it is quite easy to recover the original data and then to reconstruct the original transmission. But in the case of a Single Frequency Network , characterized by the presence of several transmitters using the same carrier frequency to broadcast the same signal, it is necessary to use directional sensors or spatial filter. In this paper, we propose two blind solutions : classical beamforming and CAPON filtering. Results of real measurements are presented.