Estimation and cancellation of high powered radar interference for communication signal collection

In this paper, we investigate the demodulation of a communication signal that is interfered by a high-powered radar signal. We choose quaternary phase-shift keying (QPSK) modulation for illustration. A least squares estimator (LSE) is used to estimate the amplitude and phase of the interfering radar signal to be used for interference cancellation. Then a maximum likelihood detection (MLD) receiver is used. We show that the QPSK SER improvement in the radar interference environment depends on collection time. For large collection times, the SER approaches the theoretical SER for QPSK. Unfortunately, as the collection time decreases the variance of the radar estimate increases, which degrades the SER. Further, we show increases in radar estimate variance as the QPSK SNR increases, which affects the SER. We propose a form of interference cancellation based on estimating the radar signal and then subtracting it from the received signal prior to MLD of the communication signal.