Comparative A-GPS and 3G-Matrix Testing in a Dense Urban Environment

P. Duffett-Smith, R. Rowe

Abstract:	It is now widely accepted that GPS alone cannot provide the quality of service needed for mobile-terminal location-based services (LBS), measured by availability, time to respond, and accuracy. The satellite signals are heavily attenuated in shielded spaces where there is no direct line of sight between the terminal and the satellite, and they are also subject to multi-path propagation so that, even when a position fix can be achieved within a reasonable integration period, the accuracy is diminished. The general solution to this problem comes in two parts. The first is to provide the terminal with an alternative location-finding method. Generally in W-CDMA and GSM, this has been the Cell-ID method by which the position of the terminal is taken to be the position of the serving cell-tower or the centroid of the area served by it. Although the Cell-ID method provides a fast result, it is generally not sufficiently accurate to smooth the transition between the one method and the other. The second part is to provide the GPS receiver in the terminal with assistance (A-GPS) sent from a server in the network. This includes satellite, time, and position information. The assistance message both reduces the delay before a GPS position fix is obtained and increases availability of GPS position fixes where the GPS data message cannot be directly decoded from the satellite signal. Matrix [1,2] is a positioning method which can be used in support of A-GPS instead of the Cell-ID method. It uses the relative times-of-flight of the signals between the cell towers and two or more terminals to calculate, simultaneously, the positions of the terminals. It is equally applicable to 2G or 3G wireless communication systems, and furthermore operates in unsynchronised networks such as GSM and W-CDMA. As a by-product, the method constructs a synchronisation map of the network and hence enables the provision of fine time aiding (FTA) to the GPS receiver in the terminal (the ‘EGPS’ method [3,4,5]). In this paper, we present the results of side-by-side testing of A-GPS and 3G-Matrix in a W-CDMA network in the Shinjuku area of Tokyo, a dense urban environment (see Figure 1). The tests were carried out over several days in 2006 in different areas of the city including high-rise close-packed concrete-and-steel structures, both outside and inside buildings. Testers were equipped with several terminals containing A-GPS and Matrix technology. Measurements were made simultaneously on all the terminals at each location. The results show the accuracy of each method, together with the percentage of attempts which were successful (i.e. the availability). We conclude that a combination of A-GPS and Matrix provides smooth, all-area, fast positioning characteristics suitable for LBS in W-CDMA networks.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	3006 - 3011
Cite this article:	Duffett-Smith, P., Rowe, R., "Comparative A-GPS and 3G-Matrix Testing in a Dense Urban Environment," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 3006-3011.
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