| Summary: | 碩士 === 國立中山大學 === 電機工程學系研究所 === 97 === In wireless location system, geometric relationship between the base station (BS) and the mobile station (MS) may affect the accuracy of MS location estimate. The effect is called Geometric Dilution of Precision (GDOP). Given the information of geometric configuration of BS and MS locations, the GDOP value can be calculated accordingly. In fact, the GDOP value is considered as ratio factor between the location error and measurement noise. A higher GDOP value indicates larger location error in the location estimator. Therefore the GDOP can be utilized as an index for observing the location precision of the MS under different geometric layout. The accuracy of location estimation can be improved by changing the BS device element locations. In the thesis, a time different of arrival (TDOA) wireless location system with mobile base station (MBS) is considered. Changing the geometric layout between the BS and the MS by relocating the MBS, the GDOP effect can be reduced and the accuracy of location estimation also can therefore be improved. Since the simulated annealing (SA) is capable of escaping the local minimum and finding the global minimum in an objective function, the SA algorithm is used in finding the best solution in a defined function based on the GDOP distribution. The best solution is then the destination of an MBS in the process of MS location estimation. When relocating an MBS from its initial location to the best location, it is likely that the MBS enters regions with high GDOP effects. To avoid the problem, the steepest descent (SD) algorithm is utilized for path planning. First, we establish the objective function which consists of the GDOP information and the angle of movement. A nearby location that has the minimum value of objective function is selected as the next move. The process continues until the MBS reaches the destination. A variety of cases are investigated by computer simulations. Simulation results show that the proposed approach can effectively find the best locations for MBSs to relocate. Based on the relocation and path planning, the GDOP effects can be reasonably reduced, and therefore the higher location accuracy is achieved.
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