Study On Wireless Location Technology In CDMA Systems

With the rapid development of the mobile communication technology, people pay more and more attention to useful location services through wide cellular networks, especially in the third generation communication systems. The location services become important and attractive and have a great future. Wireless location technology in CDMA systems is discussed in this paper. The TOA (Time of Arrival) estimation algorithms and the location algorithms based on time delay are mainly discussed. The design and implementation of the wireless location system based on them are given.Basic principles and types of cellular wireless location systems and the characteristics of CDMA2000 systems are introduced. Then the estimation and location algorithms based on TOA/TDOA and the implementation of location system in CDMA systems are discussed in detail. The method of obtaining time delay parameters with the reverse access channel is discussed. The modified algorithms of classic correlation methods of TOA estimation are proposed. Noncoherently combining algorithm and group coherent combining algorithm are given. They decrease the computational complexity and are more suitable for implementations in practical systems. The leading edge detection algorithm is proposed to mitigate the effect of multipath in TOA estimation. Then the secondary search method is proposed, it can solve the matching issue of PN code in CDMA systems. The location algorithms based on LS are discussed; include circular trilateration with LS, hyperbolic trilateration with reference differencing, hyperbolic trilateration with sequential differencing and circular trilateration with TOA differences. The design and implementation of wireless location system based on TOA/TDOA in CDMA2000 systems are given. The location process is discussed, and the hardware and software implementation of TOA estimation are given. Finally, the wireless location system which uses TOA estimation and LS location algorithms above is tested in the real environment. The test results indicate that the location accuracy of this system is better than the standard of FCC. It is a practical and valuable wireless location system.