Study On Encoding And Modulation Of Eliminating Ultrasonic Crosstalk

Ultrasonic sensors are widely used in mobile robotics for distance measurement. To provide a mobile robot with a 360-degree panorama, a sonar ring consisting of multiple such sonar sensors is required. One problem with the sonar ring operating in close proximity is the well-known crosstalk phenomenon, where one sonar sensor receives the direct ultrasonic or echo transmitted by another sonar sensor. The crosstalk can seriously decrease the measurement precision and restrict the work efficacy of the sonar ring.To thoroughly eliminate crosstalk, on the basis of studying the current references as well as analyzing experiments'results, the following main work has been completed.Considering the intrinsic inertia property of the used electrostatic ultrasonic transducer, both the Walsh code based pulse sequence width modulation and the frequency-hopping pseudorandom pulse width modulation are proposed. Comparing with the previously applied pseudorandom pulse width modulation, the two modulation methods can better adapt to the inertia property of the ultrasonic transducers and guarantee better correlation performance.The hardware system has been designed with the Digital Signal Processor (DSP) on the basis of hardware simulation using various triggering signals. The ultrasonic transmitting and receiving circuits have been set up. The framework of the software system has been set up to process the lots of data. To improve the result of correlation, the digital filter, pulse compression as well as reconstruction is applied to the received ultrasonic sequences. The Fast Fourier Transform (FFT) has been used to enhance the real-time performance of the system. Lots of experiments demonstrate that the current system can eliminate the crosstalks between two ultrasonic sensors.