Performance of hard-decision decoding of CPM schemes on the AWGN channel

The performance associated with an alternative coded continuous-phase modulation (CPM) approach of considerably reduced complexity is considered. More specifically, a concatenated approach where the decoder consists of a hard-decision (HD) CPM demodulator followed by an outboard channel decoder operating on an appropriately deinterleaved symbol stream is considered. The cutoff rate criterion, evaluated in b/s/Hz, is used to predict the performance of this concatenated coding approach. Specific code designs which are shown to achieve performance reasonably close to that predicted by cutoff rate considerations are examined. Nonbinary Reed-Solomon (RS) and various binary and nonbinary convolutional codes are considered for use in conjunction with the HD-CPM demodulator. The nonbinary codes are shown to provide better performance than binary codes. Numerical results are provided for the specific throughput of 0.83 b/s/Hz, corresponding to uncoded minimum-shift keying (MSK) which is used as a performance benchmark