Investigation On The Mobile Station Location Technique Based On SSDOA In CDMA System

Recently, with the rapid development of wireless communication, the number of subscribers has greatly increased. Wireless communication has brought great convenience to subscribers, while disadvantages of it are still coming up more and more. Since modern communication tools could be used by criminals, Public safety department has already paid more attention to the cases related to mobile phones. As wireless location techniques are able to provide the position of mobile phones, police can make use of these messages, wireless location has been a key point in the research of wireless communication.Based on the research status of wireless location techniques, this thesis proposes a location scheme based on an independent device. In this scheme, the detecting station can move anywhere in the network and is able to make use of different parameters to locate mobile stations. Meanwhile, the mobile phones and the cellular networks can work as normal. Neither is modification needed on both network and mobile stations, nor is the argument in signaling. Thus, this scheme is especially suitable for tracking criminals. The location algorithm of this scheme is the key point in this thesis. Based on the analyses of the Taylor-series method and the method proposed by Y.Chan, the basic algorithm is determined. The basic method is not so good in simulation because of the shadow fading. Thus two improving methods are proposed in this thesis: the correlation of the forward channels can alleviate the shadow fading;averaging the estimated distances can improve the location accuracy. These are proved by the simulation results. The wide use of intelligent antenna make the accurate direction measurement possible and the accurate direction measurement can improve the performance of location algorithm. The feature of the location scheme based on an independent device requires the pilot signal strength be the parameter in the location processing, but how to get the Pilot Strength Measurement Message is the key of the implementation in this scheme in cdma2000 system. Therefore in this thesis, the structure of the Pilot Strength Measurement Message isanalyzed, main factors to influence this message are determined, and several methods to obtain this message are proposed.