Complementary sets of sequences-based coding for ultrasonic array sensor

In this paper, an improved ultrasonic system for detection of falling objects or alive beings intrusion in railways is presented. The basic ultrasonic array sensor is composed of four emitters and six receivers and can be easily extended to a higher coverage area repeating this elementary structure. The receivers are able to distinguish among the signals coming from the four different emitters thanks to the signal coding with complementary sets of sequences, which also gives to the reception module an excellent process gain. The signal processing has been accomplished by means of the efficient set of sequences correlator which has been recently developed by the authors.