The impact of mismatch on the performance of coded narrow-band FM with limiter/discriminator detection

An examination of the impact of mismatch on the performance of convolutionally encoded/Viterbi decoded narrow-band FM with limiter/discriminator detection is presented. Attention was given to the potential gain available by the combination of this type of system in terms of hard and soft decision decoding. Soft decision decoding was demonstrated to offer only approximately 0.3 dB better performance than hard decision coding. It was also shown, through a technique involving the number of clicks occurring in each detection interval, that both soft and hard decision decoding bit error probability performance could be improved. It is concluded that the mismatch between the coding channel and the decoding metric of the Viterbi algorithm is responsible for reducing the difference between hard and soft decoding metrics.