A practical demodulator for continuous phase modulation

A simple method to coherently demodulate continuous phase modulation (CPM) is described, assuming carrier and symbol synchronisation. Maximum likelihood CPM receivers typically employ a metric acquisition stage followed by a maximum likelihood sequence estimator, e.g., a Viterbi decoder. For optimal demodulation, the receiver must estimate the signal component along each possible transmitted waveform, which may require a large number of matched filters. In general, 2M^L filters are necessary, where L is the length of the frequency pulses in symbol periods, and M is the number of symbols transmitted per interval. An alternative to reduce the number of matched filters is to exploit the linear dependence among signals. The proposed method is illustrated with an example of continuous phase frequency shift keying (CPFSK)