A unique, robust low-rate HF radio modem

Military HF radio modems are required to operate over a broad range of adverse channel conditions such as severe multipath and fading, partial-band and carrier-wave interference as well as Gaussian and impulsive noise. The theory of operation and simulation results for a modem capable of providing reliable, low error rate performance in the presence of these harsh forms of interference and distortion is described. The detection is maximum likelihood and is based on a partial-band noise/interference model and the assumption of slow fading. Rejection of interference is facilitated by processing in time and frequency domains. An implementation, allowing a data rate of 75 bits/s, which uses a PSK modulated carrier swept over a 3 kHz bandwidth is described in detail. Simulation results with carrier wave (CW) interference, multipath distortion, Gaussian and impulse noise conditions are presented, demonstrating the exceptional detection performance attainable