THE 1ST NYQUIST CRITERION APPLIED TO COHERENT RECEIVER DESIGN FOR GENERALIZED MSK SIGNALS

A simple procedure for designing the post-detection Alter of an MSK-ty pe receiver for Continuous Phase Modulation with modulation index h = 0.5 (Generalized MSK signals) is proposed: the criterion descends from a useful, general representation of this class of signals. The freque ncy response of the baseband receiver filter is analytically optimized in closed form whatever the modulation pulse shaping of the transmitt ed signal, and signal-to-noise ratio at the receiver. The criterion is pointed out through a significant, exact representation of Generalize d MSK signals, whatever the modulation pulse-shaping waveform, which i s assumed to be included in a time range equal to LT, T = symbol time. The main part of intersymbol interference, as appears from the repres entation of the CPM signal, is cancelled by applying the Nyquist crite rion to the most significant function among those describing the signa l structure. The numerical results obtained show a performance improve ment with respect to the Averaged Matched Filter (AMF) criterion and a re very close to the results reported in the literature, deriving from more complex design criteria. The suitability of the design criterion is also tested in the presence of interferers, showing a signifiCant advantage of the proposed filter when considering adjacent channel int erference.