Proc. SPIE. 5084, Location Services and Navigation Technologies
KEYWORDS: Cell phones, Signal attenuation, Error analysis, Networks, Time metrology, Antennas, Network architectures, Global Positioning System, Standards development, Global system for mobile communications
Finding the position of a mobile user has become important for many wireless applications. There are many methods, which fulfill this task but require extensions of the network or the terminals. The technique presented here is based on the received signal powers obtained from standard measurements. It uses a restricted search area and a time series of measurements. The search area is determined by the intersection of the maximum area covered by the serving cell and a ring determined from round-trip time measurements. A Viterbi-like algorithm is used to compare the time series of reception power levels measured by the handset with predicted values from the network planning process. It returns a weighted average of possible positions. Since only standard measurements are used, no changes of the network or the handsets are required, making the method inexpensive. Furthermore, the method can be used for traffic localization. The method has actually been implemented by Siemens for GSM. Extensive field trials in an operating network in Germany showed an accuracy of 130 meters in urban environments and about 300 meters in suburban and rural areas. Since similar measurements exist in UMTS networks, the method is applicable in UTRAN as well.