Decision-directed demodulation of frequency-shift-keyed signals

Coherent demodulation of continuous-phase frequency-shift keyed (f.s.k.) signals is achieved by generating the receiver waveforms according to previous demodulator decisions. Convolution of phase information in the signaling waveform gives rise to the possibility of an error-detection process. A particularly simple process can be implemented for f.s.k. signals with deviation ratios in the range 0.7-0.8. If the error-detection capability is combined with a request for retransmission, the undetected error performance of the system can approach the optimum for binary-data transmission. Analysis of the error-detecting performance of the system, and simulation results for demodulators employing high-resolution waveforms and binary (sliced) waveforms, are given.