Optimization of Subchannel Data Rate in FDM-SSB Transmission over Selectively Fading Media

In radio channels both time-selective and frequencyselective fading effects distort the transmitted signal. The present paper determines the effect of time and frequency selective fading upon the binary error probabilities of incoherent matched filter receivers employing postdetection diversity combining. General analytical results are specialized to the case of phase-continuous FSK and a Gaussian distribution of scattered power vs delay and Doppler shift. For this case families of curves of error probability are presented as a function of and data rate with the spread factor and order of diversity as family parameters. It is shown that an optimum data rate exists at which the binary error probability is minimized. For a wide range of cases of interest this optimum data rate is approximately two to four times the geometric mean of the fading bandwidth and correlation bandwidth of the channel. In the frequency division multiplex of a number of binary data streams on an SSB carrier, the selection of the above optimum data rate for each stream will result in a minimum over-all binary error probability for a specified bandwidth occupancy of the multiplex group.