A hybrid phase/data Viterbi demodulator for encoded CPFSK modulation

The performance of a hybrid phase/data demodulator for two CPFSK signals, one of which is band-efficient and the other of which is power-efficient, is evaluated. The demodulator algorithm can be viewed as three Viterbi demodulators operating in parallel. The performance assessment is done by computer simulation based on orthogonal functions. Static as well as time varying phase offsets are considered. These techniques can be applied to any CPFSK signal set, including Ungerboeck-type signalling for CPFSK, and can work even for phase offset processes which can change rapidly and with large magnitude. The demodulation algorithm results in a modest increase in the number of Viterbi decoder states and no increase in the number of receiver-matched filters. To track time-varying phase offsets, a truncated metric version of the Viterbi demodulation algorithm is introduced and tested.