An improved Viterbi decoder for the differential detection of continuous phase modulation schemes

A sequential decoder for the differential detection of continuous-phase-modulation (CPM) signals is introduced. The decoder is based on the use of multiple differential detectors and takes advantage of a self-encoding process introduced by the differential detection. The algorithm is derived in a general form and can be applied to any CPM scheme with any number of differential detectors. The decoder has been evaluated for the case of tamed frequency modulation (TFM) and Gaussian minimum-shift keying (GMSK) with B_tT=0.25, under additive white Gaussian noise and multipath propagation conditions. The BER performance results indicated significant gains. In additive white Gaussian noise, an improvement of 8.2 dB over the conventional differential receiver has been achieved. Under fading conditions the gains become even higher, indicating that the decoders perform significantly better than conventional detectors under multipath propagation