On the availability of trellis decoding schemes for continuous phase FSK signals employing limiter discriminator detection

Abstract

Although a trellis‐coded modulation scheme has been applied to multilevel PSK or QAM signals, its application for the continuous‐phase FSK (CPFSK) with the limiter‐discriminator detection has not been investigated well and the coding gain associated with it has not been obvious yet. In this paper, using a linear approximation, we have designed modulation parameters of this scheme. We have also executed the exact computer simulation and made clear the problem to obtain the actual coding gain as well as to increase them. Furthermore, utilizing the intersymbol interference caused by the IF filter, which greatly deteriorates the bit error rate (BER) performance in this scheme, we have proposed a sequence estimation scheme using the Viterbi algorithm. In this scheme, the sending signals are those of the binary continuous phase FSK. Through computer simulations, we have made clear that large improvements of BER really exist. The sequence estimation scheme is considered to work better than the trellis encoded scheme when considering the BER performance and the complexity of transmitter and receiver.