Research On The Key Technologies Of Quasi-GPS Ultrasonic Location System

Autonomous Guide Vehicle (AGV) is the main conveyance in modern logistics system, so people have attached much importance to the study of location and navigation technology, which is the most important part of AGV. Using the principle of Global Positioning System (GPS) for reference, Quasi-GPS ultrasonic location system is a novel location system and it's very suitable to AGV application. Starting with the problem of distance estimation between location object and location base-stations and taking the status parameter (position, velocity and pose angle) estimation as the core, the key technologies in Quasi-GPS ultrasonic location system are studied and discussed deeply in this paper by digital signal processing technologies. The follow are the major study results of the paper:1. According to signal transfer mode, ultrasonic location system can be reduced to three manners: Inverse-GPS manner, Respondent manner, Quasi-GPS manner. Firstly, the predominance of Quasi-GPS ultrasonic location system used in AGV is expatiated and its work principle, make-ups, influence factors and the design of function cells are described in detail. Then the transmission signal format from base-station and the design of constraint location space are studied. Lastly, the sameness and difference between Quasi-GPS ultrasonic location system and GPS are expatiated and the key technologies in Quasi-GPS ultrasonic location system are analyzed.2. The distances estimation algorithm between object and base-stations is studied in detail, which provides pseudo-distance observation data for location object's status parament estimation. Firstly, the single base-station distance estimation algorithm is studied, which is the foundation of multiple base-stations distances estimation algorithm. The single base-station distance estimation model is established and the envelope correlation fast time delay estimation (TDE) algorithm based on FFT and the above model is presented. Under the condition of multiple base-stations transmiting signal simutaenously, the received signal model is established. Based on the above model, the multiple base-stations distances estimation algorithm based on Short Time Fourier Transform (STFT) is presented. It shows by experiment that we can obtain exactly the distance estimation value by the above algorithm.3. After we have obtained the distances estimation values between location object and location base-stations, the static location algorithms (the analytical method using two location base-stations and the Gauss-Newton iteration algorithm using more location base-stations) are studied and their location precisions are analyzed. It shows by analysis that the location precision is revelant to distance measurement precision, base-station position's veracity and selective location base-stations. The base-station selection principles using two or three base-stations for location are presented based on the geometrical layout of the Plane Dilusion of Precision (PDOP), and lastly it is verified by simulation that the above analysis is right.4. Three additional location algorithms, i.e., the improved Gauss-Newton iterative algorithm, the intersectant circle chord algorithm, the least square estimation algorithm, are presented in view of easier realization in DSP considering of the deficiency of conventional Gauss-Newton algorithm, which involves much square-root, matrix's inversion and division operation. It shows by theory and simulation that the location precision of the improved and conventional Gauss-Newton algorithm is equivalent but the location precision of the rear two algorithms is baddish under the same condition, i.e., the same measurement error and the same base-stations for location. But the rear three algorithms are easier to be realized in DSP because they need little calculation comparing with conventional Gauss-Newton algorithm.5. The position and velocity estimation algorithms of dynamic objects are studied based on the multiple base-stations distances estimation algorithm and static location algorithm. Considering of the specialty of dynamic location objects such as AGV and AMR (Autonomous Movable Robot), the observation equations and the status equations are established. Then the "two steps" track algorithm of dynamic objects is studied: Firstly, the coarse estimation value of dynamic coordinate and velocity can be obtained by the above multiple base-stations distances estimation algorithm and static location algorithm; Secondly, put the above coarse estimation value sequence into Kalman filter. It shows by simulation that position and velocity estimation precision can be augmented further after the above coarse estimation value sequence is processed by Kalman filter.6. Using the technology of pose maeasurement in GPS for reference, the pose measurement algorithm in Quasi-GPS ultrasonic location system is studied. Three pose angle estimators are presented and their estimation precisions are analyzed. It shows by theory that the estimation precision of the estimator using arctg function is best because it takes full advantage of the position information.