Performance Evaluation of Various Decision Schemes for Frequency Demodulation of Narrow-Band Digital FM Signals in Land Mobile Radio

Frequency demodulation of narrow-band digital FM signals is attractive for land mobile radio use. However, because of intersymbol interference due to premodulation filtering, the bit error rate (BER) performance is degraded severely. Various improved decision schemes, such as decision feedback equalizer decision, three-level eye decision, and maximum-likelihood sequence estimator decision, have been proposed. In this paper, laboratory experimental results are presented on the BER and block error rate (BKER) performances achieved by the abovementioned decision schemes for 16-kb/s Gaussian-filtered minimum shift keying (GMSK) signal transmissions. Investigation of BKER performance is especially important for designing appropriate forward error correction. Field experimental results of 16-kb/s GMSK at 1.45-GHz carrier frequency are also presented to compare BER performances achieved using different decision schemes.