Vehicle Location Using GPS in Urban Areas

Hayato Torii and Yoshiaki Takechi

Abstract:	In the marine and air navigation sectors, GPS receivers are rapidly replacing conventional navigational aids such as Loran-C, Omega and TRANSIT satellite navigators in recent years. On the other hand, land use of GPS receivers is emerging as an important sector of future GPS applications. GPS receivers for land navigation are required to have the following characteristics: (1) Reduced Computational Complexity The navigation filter used in many conventional GPS receivers consists of a Kalman filter that takes measurements using signals from 4 satellites. This type of navigation filter is associated with extremely high computational complexity. One solution to this problem would be to use the most advanced hardware, however, this approach makes it impossible to develop a low-cost, low-power GPS receiver. From this point of view, it is essential to optimize the software so that the computational complexity is reduced without sacrificing the required system performance. (2) Increased Availability of Position Fm When traveling in urban areas, where satellite signals are frequently blocked by buildings, it is often experienced that au onboard GPS receiver cannot receive the necessary number of satellite signals (at least 3 for 2-D f& 4 for 3-D fm). ‘lhe GPS receiver is not adequate for land navigation if every outage of satellite signals results in an position ftx interrup tion. It is therefore essential to increase the position frx availability. (3) Improved Accuracy of Position Fix Extremely high positioning accuracyisrequiredto plot a vehicle’s track exactly along its actual route. It is particularly imporumt to minimize jumping of plots, that may occur when the combination of satellites changes. FURUNO has developed a navigation filter used in the GN-72 for car use. GN-72 is our new product. It has been designed with particular attention to provide the aforementioned characteristics, that is, reduced computational complexity, higher position fm accuracy and availability compared to earlier navigation filters. This paper provides a general description of the algorithm used in the navigation filter and reports on the results of the field tests. The test results have proved that the algorithm offers high performance for land mobii applications. It reduces the computational workload on CPU (to about l/3 compared to the conventional navigation filters used in the GP-70), increases the availability of position fix. And it improves the positioning accuracy to take all-in-view solution.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	1153 - 1158
Cite this article:	Torii, Hayato, Takechi, Yoshiaki, "Vehicle Location Using GPS in Urban Areas," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 1153-1158.
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