Design of digital polarity correlators in a multiple-user sonar ranging system

Pulsed ultrasonic distance measurement systems are frequently used in robotics applications thanks to their low cost and small size. The pulse compression techniques, originally developed by radar engineers, were adopted to eliminate frequent misreadings caused by crosstalk or external ultrasound sources. However, a few problems become apparent when implementing the pulse compression techniques in robotics applications. First, due to the implementation of correlation functions, the complexity of the total system may significantly increase. Second, if the piezoelectric transducer is excited by a chirp signal, efficiency is reduced due to the narrow bandwidth. In this paper, we present a digital polarity correlator designed for binary coded frequency shift keyed signals which increase the number of different sequences having the same length in a restricted band. The digital signal processing system is integrated into a single programmable logic device. Experimental measurements have been made, and a good agreement with reference data has been obtained with noise added.