Optimum Gaussian Filter and Deviated-Frequency-Locking Scheme for Coherent Detection of MSK

Predetection Gaussian bandpass filtering effect on the coherent detection of minimum-shift-keying (MSK) is theoretically anlayzed on the basis of the worst signal pattern which brings 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 , which degrades the required (signal-energy-per-bit to noise-power-density ratio) only by 0.14 dB from that of antipodal coherent PSK using differential encoding. 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. In addition, an alternative coherent detection using the reference carrier having the frequency deviated from the center frequency by the frequency deviation, which is called the deviated-frequency-locking scheme, is presented, and its error-rate performance is proved to be substantially identical with that of the conventional center-frequency-locking scheme.