An Efficient NLOS Error Mitigation Method for Wireless Location

Wireless location has received considerable attention over the past few years. Many techniques, such as time-based methods (TOA and TDOA), AOA based methods, and Assisted-GPS, have been proposed. Time-based methods such as TOA and TDOA, are particularly exciting since they are sufficiently accurate for E911 under ideal conditions. However, several error sources, such as NLOS (Non-Line-Of-Sight) propagation, received signal strength, and time synchronization, deteriorate performance in real-world situations. NLOS errors cannot be easily removed as they are a function of the mobile radio channel which in turn depends on the environment of the MSs (Mobile Stations) and BSs (Base Stations) and is time variant. Hence, NLOS errors are usually the limiting factor in wireless location. In this paper, an efficient NOLS mitigation algorithm is proposed. Unlike previously developed NLOS mitigation algorithms, the method here has the following important properties: • It is an epoch-to-epoch method that does not need spatial diversity and time-history. Therefore, this method can be used by low dynamic subscribers or even stationary subscribers. • It is a position domain solution and the final solution is obtained by maximizing the so-called distribution function (DF). Unlike the normal Weighted Least-Squares method in the range domain, it is a robust estimation method and the impact of NLOS errors may be automatically removed.