A high-performance reduced-complexity GMSK demodulator

A four-state adaptive MLSE demodulator for GMSK modulation (BT=0.3) on AWGN channels is analyzed and simulated. This demodulator uses the linear representation of GMSK signals and achieves the same BER performance as MSK. The channel impulse response coefficients used in the MLSE branch metric calculations are derived in closed form and adapted in a decision-directed mode to offset any performance losses incurred by retaining only one term in the linear representation. The number of states in the MLSE demodulator is reduced to two, at about 0.1 dB performance loss, by preceding it with a whitened matched filter.