OPTIMUM GAUSSIAN FILTER AND DEVIATED-FREQUENCY-LOCKING SCHEME FOR COHERENT DETECTION OF MSK.

The effect of predetection Gaussian bandpass filtering on the coherent detection of minimum-shift-keying (MSK) is theoretically analyzed for the worst signal pattern which results in the maximum intersymbol interference. The optimum 3 db-down bandwidth (B)-bit duration (T) product of the Gaussian bandpass filter is proved theoretically to be BT equals 0. 5887, which degrades the required E//b/N//O (signal-energy-per-bit to noise-power-density ratio) by only 0. 14 db from that of antipodal coherent PSK using differential coding. The degradations due to the phase errors of reference carrier and decision timing and the frequency drift of the received input signal are also shown. An alternative coherent detection scheme using a reference carrier having its frequency deviated from the center frequency by the frequency deviation is presented, and its error-rate performance is proved to be substantially identical to the conventional center-frequency-locking scheme.