Estimating temporal multipath via spatial selectivity: Building environmental knowledge into waveform design for radar-embedded communications

We consider the problem of embedding a communications signal into the backscatter induced at an RF tag/transponder by pulsed radar illumination given the competing constraints of high data rate and low probability of intercept (LPI). In this work spatial selectivity is addressed as a means to provide lower intercept probability without sacrificing data rate or receiver error performance. Here spatial selectivity is achieved by incorporating the forward scatter (i.e. multipath) effects between the radar and tag into the information-bearing embedded communication waveform intended for reception at the radar. The multipath is incorporated via a time reversal framework thereby enabling spatial focusing which inhibits interception by an eavesdropper. The focus of this paper is upon the accurate estimation of the multipath given that prior knowledge of the transmitted radar waveform may not be available.