Viterbi Decoder on HF Channels

A new HF modem that relies on Viterbi decoding is described. This software-implemented low to medium rate HF modem incorporates convolutional codes with interleaving and soft Viterbi decoding. Its performance is compared to the theoretical one, as well as to that of an existing, widely used HF modem. It is shown that the interleaved Viterbi decoder and the selective in-band diversity combiner provide superior performance, both under selective fading and additive wideband and narrowband interferences.