Mobile position location estimation in cellular systems.

摘要

Providing the accurate location information of the Mobile Station (MS) for Emergent 911 call has become mandatory in the States, and is of great interest for location related applications. We have studied the Cellular-Based location system, which is a location system overlaid on the existing cellular system with or without modifications. Four technical challenges in cellular-based location systems are identified as accuracy improvement, hearability problem, Non-Line-of-Sight (NLOS) problem, and network aspect.; We analyze the hearability problem in a CDMA cellular system complied with the IS-95 standard on both forward and reverse links. Motivated by the hearability challenge, we propose the enhanced measurements on pilot channels to increase the location coverage area and improve the location accuracy in CDMA based location systems. The basic idea is to obtain the Time Difference of Arrival (TDOA) measurements derived from the timing information of several pilot signals by increasing the integration time at the correlator of a MS. It is shown that performance of the location system is a tradeoff between the accuracy requirements, location service coverage area, and processing time.; We have developed an algorithm to mitigate the location estimation error caused by NLOS errors when NLOS measurements are not identifiable. This algorithm, referred to as Residual Weighting algorithm (Rwgh), is compared with two other generic algorithms and tested under various scenarios and NLOS error models. Rwgh has shown the effective NLOS error mitigation capability in location estimation from the simulation results.; Due to the constraint on the network processing speed, the frequency of getting geolocation measurements from base stations (BSs) is limited. We investigate the optimal polling pattern to extract the range measurements under this polling frequency constraint. We have presented an analytic framework to gain the understanding of estimation accuracy by calculating the CRLB (Cramer-Rao Lower Bound) on the error of the estimation parameters and further apply the CRLB to estimate the location error by extrapolating ahead when no valid measurements are present.; Observing the intermittent and erroneous location estimates obtained from the cellular-based location system, we propose a cellular-based location tracking system to make the best use of the range measurements and supplementary information obtainable in cellular systems. The NLOS mitigation algorithm developed previously is used to improve erroneous location estimates corrupted by NLOS errors. The performance of the proposed cellular-based location tracking system is evaluated through simulations. (Abstract shortened by UMI.)