Using time reversal of multipath for intra-pulse radar-embedded communications

This paper considers the problem of embedding a covert communication waveform into the backscatter from an illuminating radar by an RF tag/transponder within a multipath environment. We propose to exploit the multipath via time reversal, which is ideally suited for backscatter communications. Multipath time reversal induces a spatio-temporal focusing of the embedded communication waveform at the desired receiver while distorting it at all other locations thus further reducing the probability of intercept. Specifically, the paper addresses the case where the radar waveform is known to the tag/transponder thus allowing for estimation of the multipath via coherent processing (i.e. pulse compression). Within the radar-embedded communications context the use of the estimated multipath is compared with the case when no multipath knowledge is employed.