High Accuracy, Low Cost Integrated Positioning System for the Toronto Transit System

M. Abd El-Gelil and A. El-Rabbany

Abstract:	Until recently, transit systems used old technologies such as odometer/gyro sensors and signposts for position determination. The Toronto Transit System is no exception. Combining the measurements from the odometer and the gyro, the bus’s position can be determined with respect to an initial (known) position. Unfortunately, however, both the odometer and the gyro drift over time, which cause significant error in the estimated position. Signposts, on the other hand, are radio beacon transmitters that are placed at known locations along the bus routes. Each beacon transmits a low power microwave signal, which is detected by a receiver on the bus, to account for the odometer’s drift error. Unfortunately, this system has a number of limitations, including its incapability of knowing the exact location of a bus in-between two signposts. In addition, it is not possible to track a bus that goes off-route as a result of, for example, a road closure. To overcome the limitations of the above conventional systems, an integrated positioning system is proposed. The integrated positioning system consists of a low-cost autonomous GPS system, supplemented by the existing dead reckoning (DR)/signpost system. With the integrated system, GPS helps in controlling the drift of the DR system through frequent calibration, while the DR becomes the main positioning system during the GPS outages. An optimal positioning solution is obtained using Kalman filtering technique, which utilizes all the available sensor information. The biases of the conventional sensors are modelled as first order Gauss-Markov process. In addition, we take advantage of the frequent bus stops to estimate the gyro bias error. To further increase the accuracy of the integrated system, the signposts are used as reference stations to account for the remaining GPS/DR residual errors.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1766 - 1770
Cite this article:	El-Gelil, M. Abd, El-Rabbany, A., "High Accuracy, Low Cost Integrated Positioning System for the Toronto Transit System," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1766-1770.
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