CDMA multiuser radiolocation

Wireless location refers to obtaining the position information of a mobile subscriber in a cellular environment. Such positioning information is usually provided in terms of geographic coordinates of the mobile subscriber with respect to a geographic reference point. Wireless location finding has emerged as an essential feature of cellular systems and has many potential applications in areas such as location sensitive billing, asset tracking, fraud protection, mobile yellow pages, fleet management and the list continues to grow and so does the location based services market. Several location techniques utilizing terrestrial wireless network elements and radio signals have been proposed over the years. However, accurate mobile station (MS) positioning in a terrestrial wireless system is impeded by multipath propagation, low signal-to-noise ratios (SNRs), multiple access interference (MAI), and non-line-of-sight propagation. While subscriber location has been previously studied for code division multiple access (CDMA) networks, the effect of multiple access interference has not been fully explored especially for the case of closely spaced multipaths. Traditional location algorithms have derived location estimates usually assuming single user single path environment. However this assumption is not correct as measurement bias will be introduced due to MAI. We propose non linear filtering approach based on unscented Kalman filter (UKF) for MS delay estimation that is subsequently used for multiuser radiolocation. We show through simulations that the proposed method provides MS position location quite accurately in the presence of MAI for closely spaced paths.