The use of binary coded frequency shift keyed signals for multiple user sonar ranging

In pulsed ultrasonic distance measurement systems, the pulse compression techniques were adopted to eliminate frequent misreadings caused by crosstalk or external ultrasound sources. In an earlier paper, we have described a pulse compression system based on digital polarity correlators where both input signals are infinitely clipping and converted to binary representations before correlation. We report here the results of comparative experimental studies of the use of frequency shift keying and phase shift keying for the pulse compression system when using piezoelectric transducers. The codes are generated with a combination of simulated annealing and hill climbing, to minimize the maximum sidelobe in the autocorrelation as well as minimize the peaks in the cross correlations. The results demonstrate that the signal to noise ratio of the frequency shift keying system is better than that of the phase shift keying system in the narrow-band operation.