The Study Of The Key Technologies For Short Baseline Positioning System

21stcentury is a century of ocean, and the underwater acoustic technology based on sounddetecting is the most effective means to achieve and transform underwater information. Thisarticle mainly deals with short-baseline based high-precision location technology, whichprovides high-precision location devices for robots detecting and working underwater.Multi-path time delay estimation error is one of the important factors that affect theprecision of a location system. Due to the multi-path feature of the underwater acousticchannel, direct sound signal mixes with multi-path reflected sound, which affects the sonardetector’s judgment. Utilizing the multi-path characteristic of a time-reversal focusingchannel, this paper proposes a new strategy to mitigate the multi-path effect of the underwateracoustic channel, namely an improvement of short-baseline location system. A technologycombining short-baseline and single array time-reversal mirror method is raised. Also, thefocusing gain of the proposed method is analyzed. In this paper, time-reversal locationmethods, asynchronous initiative respond and single array based synchronous virtual beacon,are used to mitigate the multi-path effect and improve precision of location. A method basedon the channel focus function of time-reversal mirror to resolve problems such as near-fareffect and multi-target distinguish of multi-target location system is also proposed.Focused on detection issue of the short-baseline sonar, the paper analyses and deduces theperformance of the common matching filtering detector, time-reversal matching detector,common maximum likelihood estimator and time-reversal maximum likelihood estimator.Especially, for the detection performance of the sonar detectors in unstable background suchas multi-path effect of the underwater acoustic channel, reverberation and noise edge, it putsup with a CFAR detector of varying index, namely VI-CFAR detector. The VI-CFAR detectorhas strong capacity of self-adaptation and anti-interference. It not only does well in falsealarm probability control, but also requires small calculating amount, which makes it a steadydetector.The paper analyses the influence of the base array to location precision in detail, and putsforward a high speed random placed short-baseline underwater acoustic location system. Asfor the short-baseline array’s correction, the paper aiming at minimizing the array interference vector, starts from the factor of total error and proposes a method to mitigate the influence ofinterference error by utilizing restraint Least Square Method. Due to the characteristic of thesame error source in locating system, the paper uses adjacent array nodal point as differentialreference nodal point to correct unknown nodal points. Then combine Least Square Methodfor iterative solution. The proposed method has simple structure and high engineeringapplicability.At last the paper demonstrates and realizes a short-baseline location system used forunderwater robots. The design idea and implementation plan of software and hardware ineach module are also introduced carefully. In addition, the test results of the system underdifferent condition such as pool, multifunction wave-producing pool and the sea are provided.It is proved that the system is of great reliability in various circumstances and its locatingprecision even ranges within0.5%, which satisfies the system requirements. It copes with thebreakpoints occurred in the process of locating through some manners like round filter,mid-value filtering and Kalman filtering, which contributes to its good effect for pathsmoothing.