UPGRADE an Indoor Positioning System Using a Standard GPS Receiver

J. Caratori, M. Francois, N. Samama

Abstract:	UPGRADE (Universal Positioning Theory Based on Global Positioning System) approaches have already been described [1]-[2], showing that it was theoretically feasible to use so-called "GPS repeaters" to implement an indoor positioning system which will allow a standard GPS receiver to give accurate indoor location information. The subject of this paper is now to present the practical way to implement the approach that uses "RnS" repeaters, which transmit the signals of all the visible satellites from outdoors to indoors. We also present experimental results that confirm the possibility to achieve an indoor positioning system accurate to a few meters (basically the same receiver accuracy as outdoors). The methodology followed was to design a satisfactory repeater, to work on specific programs to drive the indoor GPS receiver and to compute data towards the distance "d" separating the repeater antenna and the receiver. Concerning the programming approach, let us first recall that when using such a repeater, the indoor receiver computed fix gives the repeater receiving antenna location. But it also provides an indoor receiver clock bias that is the sum of the real internal clock bias, the repeater induced delay and the signal propagation time required to reach the indoor receiver from the emitting repeater antenna. This time corresponds to the distance "d" we are so interested in. Thus, since the induced repeater delay is a known value, and as long as we have the means to know about the drift of the internal clock bias, it is possible to get the variation "D(d)" of the distance "d", from one fix to another. Experiments have been carried out to do this. We show how precisely it is possible to calculate d in this 1-D approach: typical values of less than 1 meter have been obtained. To achieve a full positioning system, UPGRADE states that 3 or 4 such repeaters are required for a complete global system. Experiments with 3 have been carried out that allowed a 2-D location to be computed, assuming we are moving on a given floor of a building. As a matter of fact, a 1-meter accurate altimeter could be used to help in the determination of the floor. Experimental results have shown typical 1 to 2 meter accuracy in positioning capabilities in an open space (light multipath) environment. With these first results, we feel confident in designing a fully integrated GPS receiver that will have indoor accuracy as yet unknown. The global indoor system architecture is still to be improved, taking into account different types of applications and environments, but the very simple theoretical method has proved to be a credible alternative to pseudolites or Enhanced-GPS (high sensitivity) solutions [3]. The next steps are to achieve this full indoor positioning system with 4 RnS repeaters and to improve the computations.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	593 - 602
Cite this article:	Caratori, J., Francois, M., Samama, N., "UPGRADE an Indoor Positioning System Using a Standard GPS Receiver," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 593-602.
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