Research On Eliminating Ultrasonic Crosstalk Based On Pseudo-Random Frequency-Modulated Pulse Sequence

Ultrasonic range sensor (also called sonar in this thesis) has become a kind of indispensable range sensor used to acquire environmental information for mobile robots due to its low price, simple hardware interface and relatively accurate distance measurement. To provide mobile robots with more environmental information, normally a sonar ring consisting of multiple sonar sensors is required. When multiple sonar sensors work simultaneously, one serious and ubiquitous problem, the so-called ultrasonic crosstalk, will occur. The crosstalk means that one sonar sensor receives the ultrasound or ultrasonic echo transmitted by another ultrasonic transducer, instead of its own, which will result in the error distance measurement.A novel Pseudo-Random Frequency-Modulated (PRFM) pulse sequence used to fire ultrasonic transducer is put forward in this thesis. The PRFM pulse sequence is composed by 16 fixed-width and fixed-amplitude short pulses, in which the duration between two neighboring pulses is determined by pseudo-random number sequence. To ensure that the sequence could be used to fire ultrasonic electrostatic transducers, its frequency range is designed to be within the work bandwidth of the used ultrasonic transducer. Combing the correlation technique, the crosstalk can be identified and eliminated because firing sequence of every transducer is unique.The experiment platform for solving the crosstalk problem of two ultrasonic transducers is set up, where a TMS320VC5402 DSP chip is used as the data-processing core. The PRFM pulse sequences are generated by software and sent out through DSP pins. A drive circuit is designed for electrostatic ultrasonic transducer. To ensure the real-time character of signal processing, FFT (Fast Fourier Transform) is used to implement correlation algorithm.