Cramér-Rao Lower Bounds for hybrid localization of mobile terminals

While in outdoor scenarios the global positioning system (GPS) provides accurate mobile station (MS) location estimates in the majority of cases, in dense urban and indoor scenarios GPS often cannot provide reliable MS location estimates, due to the attenuation or complete shadowing of the satellite signals. The existing cellular radio network (CRN)-based localization methods, however, provide MS location estimates in almost every scenario, but they do not reach the accuracy of the MS location estimates provided by GPS. Hybrid localization methods combine MS location information available from measured values of the CRN with MS location information provided by the measured values of GPS. In this paper, a hybrid localization method is proposed that combines received signal level and timing advance measured values from the global system for mobile communication (GSM) and time of arrival measured values from GPS. The best achievable localization accuracy of the proposed hybrid localization method is evaluated in terms of the Cramer-Rao Lower Bound. It is shown that the hybrid localization method significantly improves the localization accuracy compared to existing CRN-based localization methods.