Research On Anti-jam Techniques For Ultrasonic & Infrared Positioning System

Ultrasonic and infrared positioning technology, which completes location by measuring time of flight (TOF), is widely applied in electronic whiteboard, robot navigation, virtual reality etc. In practical applications, the acoustic radiation and reflection interference, infrared interference and electromagnetic interference can seriously affect the positioning performance of the system, even can cause the system positioning function failure. improving the capability of anti-jamming is still a main technical problems for ultrasonic and infrared positioning system.Based on ultrasonic and infrared white board system , this dissertation studies the inhibit algorithm of acoustic radiation and reflection interference, which completes hardware optimize design of infrared interference and electromagnetic interference, and comprehensively improves its adaptation of the environment.For the problems of acoustic radiation interference, we analyze about 4,000 measurement data, and find that the acoustic radiation interference makes envelope of received signal have a breakpoint, study inhibit algorithm of the acoustic radiation interference according to the characteristic information. We obtain the breakpoint time of measured signal by the maximum second-order difference quotient, and then obtain time of ideal ultrasonic signal corresponding with the breakpoint, and replace the measurement waves before breakpoint with the Taylor series expansion of ideal ultrasonic signal about the breakpoint in order to eliminate the effects of acoustic radiation interference. Simulation results show the algorithm can effectively restore ultrasonic signals under the presence or absence of the acoustic radiation.The quantitative relationship of system measurement error with artificial random operations and non-uniform grid is deduced. The performance of acoustic radiation interference suppression algorithm is compared with correlation method, NLMS algorithm. When error points are not more than 46, the computation of the proposed algorithm is less than the typical method of 1/10, which provides a theoretical basis for practical application.We proposed an inhibited algorithm, which combine optimized dynamic dual-threshold with cross-correlation for acoustic reflection interference. Firstly, it applies rough correlation algorithm to judge the existence of acoustic reflection interference, then uses the optimized dynamic dual-threshold method to extract fuzzy time delay and completes separation of signal and interference, and finally applies fine correlation algorithm to get accurate time delay. Simulation results show the proposed algorithm not only can eliminate the effects of acoustic reflection interference, but also satisfies the acquirement for accuracy of 0.5mm.For inhibition of infrared and electromagnetic interference, we completed a optimized design, which includes low-noise receiver circuits, infrared and low noise PCB, and achieved signal to noise ratio of low noise amplifier is not less than 10dB, the interference voltage peak of infrared circuit is no more than 800 and so on, reduced the effects of these interferences for the positioning performance of the system.The innovation ideas of this paper are as follows:(1) According to analysis of about 4,000 measured data, and find that the acoustic radiation interference makes envelope of received signal have a breakpoint. Based on the characteristic of the breakpoint information, we propose an acoustic radiation interference suppression algorithm, which applies ideal ultrasonic signal to replace the sigals before breakpoint. Simulation results show the proposed algorithm eliminate the effects of acoustic radiation interference..(2) The mathematical expression of the relationship between artificial random operations, non-uniform grid and system measurement error is derived, which is theoretical basis of the algorithm error analysis. The algorithm computational and error points of acoustic radiation interference suppression algorithm are compared with the typical algorithms, and verifies the feasibility and superiority of the proposed algorithm.(3) We propose a joint inhibited algorithm of optimized dynamic dual-threshold and cross-correlation for acoustic reflection interference, which completes separation of signal and interference, and satisfies the acquirement for dynamic accuracy of 0.5mm. The inhibited algorithm improves ultrasonic and infrared positioning system adaptation of the environment.The above works provide new methods for ultrasonic and infrared positioning system theoretical research of anti-jamming, and provide solutions for improving the environmental adaptability of the system, which has a certain reference value for the research and development of the whiteboard, virtual reality tracking devices and other products.