Performance Analysis For The Ultrasonic Spread Spectrum Ranging System Excited With Pulse Codes

There exist two major problems in a multi-channel ultrasonic ranging system, one is the crosstalk phenomenon, and the other is contradiction between effective ranging distance and ranging resolution. To solve the two problems, spread-spectrum technology and coding method are applied to the ultrasonic ranging field. The pulse-code-modulation sequences are used to drive the ultrasonic transmitting device and the correlation method is adopted to calculate the TOF (time of flight) at the receiving end. Since the information encoded in the excitation sequence is unique for each transducer, the multi-channel ultrasonic ranging system can identify the source transducer of the echo sequence and the crosstalk phenomenon can be eliminated then. The spread-spectrum technology can enable the ultrasonic ranging system to own a longer effective ranging distance using long excitation sequences and to improve the ranging resolution.Based on ultrasonic spread spectrum coding ranging theory, six kinds of pseudo-random binary codes, i.e., m sequence, chaos sequence, Gold sequence, balanced Gold sequence, Legendre sequence and Hall sequence, are chosen for the multi-channel ultrasonic ranging system. Their definitions are introduced, the characteristics are analyzed briefly and the concrete generation procedures are presented.The six kinds of codes combined with three types of binary modulation technique, i.e., BASK (binary amplitude shift keying), BFSK (binary frequency shift keying) and BPSK (binary phase shift keying), are used to construct eighteen kinds (each kind includes eight different sequences) of pulse-coded digital-modulation excitation sequences. Three indexes, which are correlation degree of echo sequences, energy/energy efficiency of excitation and echo sequences, and main-lobe width of correlation function, are set to evaluate the performances of each excitation sequence.On basis of the eighteen kinds of excitation sequences, further research work has been done. Firstly, the simulation experiments are performed and the results are analyzed using the three evaluation indexes. Secondly, the ultrasonic transmitting-receiving circuit and the power module are designed to improve the structure of the ultrasonic ranging system, and ultrasonic ranging experiments are performed on this platform. Finally, analysis results of the real experiments are compared with those of the simulation experiments, and the suitable codes and modulation modes are proposed for ultrasonic spread-spectrum ranging systems.