Covert Half Duplex Data Link Using Radar-Embedded Communications With Various Modulation Schemes
Technical Report,15 Sep 2015,15 Dec 2017
Naval Postgraduate School Monterey, CA United States
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We consider the design of a low probability of intercept LPI half-duplex communications system in which the downlink is established via communications signals embedded in a pulsed-radar Doppler waveform. Previous works suggest to embed the communications in the radar backscatter where it has been shown possible to recover and demodulate communications signals that are coincident with the radar pulses in time and frequency using quadrature phase-shift keying QPSK modulation. Unfortunately, such an approach presents difficulty for a two-way link. In this work, we present a LPI half-duplex design where the downlink communications are embedded in the radar transmission, while the uplink may be transmitted via another covert method after the radar initiates communications. We illustrate the downlink using binary phase-shift keying BPSK, QPSK, eight phase-shift keying 8PSK, quadrature-amplitude modulation QAM, and explore a non-standard 8PSK for LPI. We show that probability of detection for the radar is actually improved by correlating to the radar-downlink signal. We also show that the downlink is feasible via symbol error rate SER results by estimating the radar signal parameters and subtracting the radar waveform from the received signal prior to demodulation. Further, we explore a qualitative analysis of this communications method to measure its covertness using the signals complex plane.
- Active and Passive Radar Detection and Equipment
- Radio Communications