On the Performance of Hybrid GPS/GSM Mobile Terminal Tracking

The Global Positioning System (GPS) has become one of the state-of-the-art location systems that offers reliable mobile terminal (MT) location estimates. However, there exist situations where GPS is not available, e.g., when the MT is used indoors or when the MT is located close to high buildings. In these scenarios, a promising approach is to combine the GPS measured values with measured values from the Global System for Mobile Communication (GSM), which is known as hybrid localization method. In this paper, a hybrid MT tracking algorithm based on a Rao-Blackwellized unscented Kalman filter (RBUKF) is proposed that combines pseudoranges from GPS with timing advance and received signal strengths from GSM. Simulation results show that the proposed hybrid method outperforms the GSM method. Furthermore, the performance of the RBUKF is compared to the extended Kalman filter and the corresponding posterior Cramer-Rao lower bounds.