Characterization of Range Sidelobe Modulation Arising from Radar-Embedded Communications

When information sequences are embedded into radar waveforms by means of coding diversity, the resulting radar emissions then change on a pulse-to-pulse basis during a coherent processing interval (CPI). As such, pulse compression of these different waveforms leads to different sidelobe structures, giving rise to range sidelobe modulation (RSM) of the clutter. The presence of RSM induces a partial loss of coherency after Doppler processing, resulting in residual clutter after cancellation, and hence reduced target visibility. Here the RSM effect is mathematically characterized within a phase-modulated radar-embedded communication framework. A closed-form expression for the expected value of the residual clutter power, referred to as the RSM power, is derived. The RSM power is found to not be dependent on the Doppler frequency or time-bandwidth product, but is a decreasing function of the number of pulses in the CPI and an increasing function of the modulation index. The latter controls the amount of phase shift within the radar pulse due to each communication symbol.