A 300 to 3600 bps multi-rate HF parallel tone modem

There have been many HF modems developed for voice frequency (3 kHz) operation. To achieve a certain bit rate it has been customary to select a particular waveform, error-control code and signalling protocol specifically for that rate. This methodology is unsuitable in adaptive systems, that regularly reconfigure the modem bit rate, because of the time needed to re-establish useful information flow after every configuration change. In this paper we describe a 16-tone parallel-tone modem that avoids this problem by making the information rate determined solely by the coded modulation selected. Results are given for rates of 300, 600, 1200, 2400 and 3600 bits per second (bps) on CCIR multipath fading channels. The results show that this multi-rate modem offers superior performance to contemporary modems while also supporting rate adaptation.