Pulse Coded Excitation And Time-of-Flight Estimation Of Ultrasonic Spread Spectrum Range

In view of the contradiction between the range resolution and the effective distance in conventional single-pulse ultrasonic ranging systems and the cross-talk phenomenon in multichannel simultaneously triggered ultrasonic ranging systems, the spread-spectrum coded-excitation ultrasonic ranging method is researched. For a spread-spectrum ultrasonic ranging system, the excitation sequence constructed using code-and-modulation technique for each ultrasonic transducer is unique. A pulse compression or correlation technique in the receiving circuit is used to identify the echo of the transmitted ultrasound. To decrease the blind area and improve the ranging accuracy of the ultrasonic ranging system, the time-of-flight (TOF) estimation method for the short-distance single-pulse ultrasonic ranging system is also studied.This dissertation focuses on the pulse-coded excitation of the spread-spectrum ultrasonic ranging system and the TOF estimation of the single-pulse ultrasonic ranging system. The achievement can be concluded as follows.Two performance indices, i.e., the energy efficiency and the echo sequence correlation degree, are defined. The energy efficiency reflects the ratio between the energy of the echo and that of the excited sequences of the spread-spectrum ranging system in a certain distance. High energy efficiency can increase the echo energy and the effective measurement range. The echo sequence correlation degree reflects the uniqueness of the excitation signal. Low echo sequence correlation degree, that is sharp autocorrelation and flat cross correlation, can improve the pulse-compression effect and help eliminate the cross talk between ultrasonic transducers.Four kinds of analog-modulation pulse-excitation-sequence construction methods, which include spectrum-optimization chaotic pulse position modulation (CPPM), chaotic pulse width modulation (CPWM), linear frequency modulation (LFM) and nonlinear frequency modulation (NLFM), are proposed. The genetic algorithm (GA) or nondominated sorting genetic algorithm-II (NSGA-II) is applied to optimize both the energy efficiency and echo sequence correlation degree of the CPPM, CPWM and NLFM pulse-excitation sequences. The parameters configuration method of an eight-channel LFM pulse-excitation sequences is analyzed. Comparison experiments using the eight-channel ultrasonic ranging system excited with the four kinds of analog-modulation sequences have been conducted. Six kinds of digital-modulation pulse-excitation sequences are constructed and compared. The binary chaotic series and m sequences combined with digital-modulation technique are used for constructing spread-spectrum coded-excitation sequences of multichannel ultrasonic ranging systems. The parameter configuration and GA optimization method of binary amplitude shift keying (BASK), binary frequency shift keying (BFSK) and binary phase shift keying (BPSK) pulse-excitation sequences are discussed to increase the energy efficiency and decrease the echo sequence correlation degree. Comparison experiments using the eight-channel ultrasonic ranging system excited with the six kinds of digital-modulation sequences have been implemented.The TOF estimation method based on a square-root unscented Kalman filter (SRUKF) for the single-pulse ultrasonic ranging system is proposed. The TOF is estimated by applying the SRUKF to identify the parameters of the echo signal envelope. Considering the effect of the initial state on the convergence speed of filters, multiple SRUKFs (Multi-SRUKF) in which each has a different initial state are used to estimate the TOF. The comparison experiments of the unscented Kalman filter (UKF), SRUKF, Multi-UKF and Multi-SRUKF algorithms using simulated echo signals and actual echo signals have been conducted.