Performance of the cross-correlator receiver for binary digital frequency modulation

The error probability of the cross-correlator receiver for binary digital frequency modulation (FM) is studied using theoretical analysis and computer simulations. The bit error rate (BER) results obtained permit the selection of an optimum combination of modulation index and receiver bandwidth. The BER performance of the cross-correlator is compared to that of the limiter-discriminator and found to be similar. This is noteworthy because the structure of the cross-correlator is ideally suited to DSP chip implementation and furthermore severe amplitude limiting does not have to be performed on the input signal to the receiver. Input signal amplitude variations of up to 20% of the average signal value can be tolerated with a 1 dB loss in performance. The receiver structure has the same form as for QPSK or QAM modulation. Thus a generalized demodulator that would demodulate QPSK, QAM or digital FM can be realized. The theoretical analysis [Farrell, 1993] of the receiver uses a Fourier series approach [Tjhung and Whittke, 1970] which takes into account the effects of FM distortion and intersymbol interference (ISI). Theoretical and simulation results are found to agree within 0.5 dB in E_b/N_o. The authors also address the issue of timing recovery. Results obtained indicate that losses due to timing error can be reduced to less than 0.5 dB in E_b /N_o