Performance evaluation of various decision schemes for frequency demodulation of narrow-band digital FM signals in land mobile radio

The decision feedback equalizer (DFE), three-level eye, and maximum-likelihood sequence estimator (MLSE) decision schemes for frequency demodulation of 16-kb/s GMSK signals are evaluated. Laboratory experimental results on bit error rate (BER) and block error rate (BKER) performances are presented. In additive white Gaussian noise channels, two-bit DFE achieves the best BER performance, whereas MLSE is the best for cochannel interference-limited channels. BKER performance was also examined. The three-level eye decision is a bit-by-bit decision, and thus has superior performance because there is no error propagation. In fading environments, however, this superiority tends to diminish because bursty errors due to deep fades predominate rather than error propagation effects. Some of the laboratory experimental results have been confirmed with field experiments at a 1.45-GHz carrier frequency