Coded Excitation And Echo Processing Of Non-Crosstalk Ultrasonic Ranging System

The crosstalk between ultrasonic transducers can seriously restrict the accuracy ofultrasonic ranging system (URS). The ultrasonic crosstalk sources are analyzed. Onthe premise of real-time performance of the URS, the Pulse Position Modulation(PPM) is proposed to construct the short triggering sequence for each ultrasonictransducer in order to eliminate ultrasonic crosstalk. The correlation analysis isapplied to identify the echo sequence. The chaotic mapping method and themultiplicative congruential method for generating pseudorandom numbers areintroduced. The statistical characteristics of these numbers are analyzed, and theproper numbers for real-time non-crosstalk URS are found. The relation betweenpulse's duty cycle and energy of harmonic components are deduced. To obtain theoptimal correlation performance, the genetic algorithm (GA) is adopted to optimizethe duration between pulses.The impulse response of sonar sensors is normalized to satisfy the requirement ofwavelet filter for function construction, and then is used as the wavelet filter. Thewavelet function based on echo sequence is constructed and used to analyze theechoes of PPM triggering sequences. The approximation coefficients, obtained fromwavelet decomposition, instead of the original echoes, is used to do auto- andcross-correlations, the results are remarkably improved. The length of the PPMtriggering sequence is shortened and the blind ranging zone is reduced.Using correlation of approximation part as objective function to optimize theduration between pulses with GA, the correlation performance has been furtherimproved. The results demonstrate that the non-crosstalk real-time URS can berealized provided that the duration between pulses is adjusted properly and the echoesare processed bysuitable wavelet.