Performance estimations of mobile terminal location with database correlation in UMTS networks

The most important cellular location application area is security service, where new terminals must support location within 50-150 meters. Only GPS or short-range systems provide the ultimate resolution below 10 m. The coarse-level location can rely on cell identification. More accurate methods are based on time or time difference of arrival, angle of arrival or signal strength measurements. Multipath propagation, the lack of a line-of-sight path and the hearability problem may hamper OTDOA-type performance in UMTS. The database correlation method (DCM) enables positioning with fewer measurements and avoids multipath problems. The idea is to use a previously collected signal database from the coverage area. The telephone measures the same parameter and sends it to the location server. Position is determined by correlation, which compares the measured and stored signal parameters. DCM can exploit the wide UMTS bandwidth by using the measured power delay profiles and location estimation is possible by using only one base station. Results imply a need of two different measurement layers: signal strength and power delay profile. Direction measurements can further narrow the possible physical area. The drawbacks are the unstandardized measurement procedure of the power delay profile, its reporting and initial field measurements. Our simulations with 24 sites and 57 cells indicate DCM accuracy within 25 meters (67 percent) and within 188 meters (95 percent).