Data detection and timing recovery for a noncoherent discriminator-based GMSK receiver

The authors examine the effect of various B_t T,h combinations (B_t=premodulation filter bandwidth T=bit period, h=modulation index), various IF (intermediate frequency) filter types, and various IF filter bandwidths on the performance of a noncoherent GMSK (Gaussian minimum-shift keying) receiver. Numerical results are presented for bit error rate (BER) performance of the data detection subsystem and for phase jitter within the timing recovery subsystem. Results show that BER is very sensitive to IF filter type and bandwidth and that phase jitter is very sensitive to IF filter bandwidth. The test practical IF filter for the noncoherent GMSK receiver is a phase-equalized Butterworth filter. A filter order of 6 or 8 poles is sufficient for noise rejection, but higher order may be required to satisfy adjacent channel interference requirements. Although data detector performance is optimized with an IF filter bandwidth of B_tT=1.1, this increase in bandwidth does not significantly affect data detector performance