UPGRADE RnS Indoor Positioning System in an Office Building

Julien Caratori, Marc Francois, Nel Samama and Alexandre Vervisch-Picois

Abstract:	The present paper will describe the latest results of an UPGRADE RnS indoor positioning system obtained in a typical office building. The theoretical approach is briefly summarised with details of the actual implementation of the processing, showing how it is possible to make the best use of current GNSS receivers’ capabilities. Then experimental set-up and results are presented. The UPGRADE RnS indoor positioning system is based on the use of so-called GNSS repeaters that, in the case of this RnS system, have the role of collecting the GNSS signals in the best possible environment (namely outdoors on the roof of the building). Then the second role is that of a transmitting system that forwards these signals into the indoor environment, without any further treatments other than amplifying. In such a case, it is well known that the indoor computed navigation solution with any current GNSS receiver is the location of the outdoor receiving antenna. The UPGRADE RnS approach takes advantage of the fact that within the fourth co-ordinate of the navigation solution, i.e. the receiver clock bias, lies the distance that separates the indoor transmitting antenna of the repeater to the indoor receiver antenna. Various papers have already described the theory and have also experimentally shown the potential of such a technique [1]. The purpose of the present paper is to develop further this approach by the way of experimental studies in an office building. The experimental set-up consists of a single outdoor antenna that is linked (through a coaxial cable) to the core of the system: an amplifying part that boosts the GNSS power level, a dispatching part that allows the splitting of the incident signal into 3 or 4 identical signals (depending on the number of repeaters) and the cycling machine that permits the necessary temporal cycle to be carried out. Furthermore, the last part of the system is of course the repeater itself: it is composed of an amplifier driven by the cycling machine and a passive antenna used for emitting purposes. A large number of experiments have been carried out with different goals. The first one was to precisely determine the best processing for indoor location determination. We then computed data such as calculated clock bias (from the position calculation) or calculated clock bias drift (from the velocity calculation), but we also tried to evaluate the utility of raw measurements. Once achieved, our purpose has been to evaluate the global system architecture efficiency. The first important point to take into account when one will try to draw a comparison between indoor positioning solutions (pseudolites, wireless LAN, mobile networks or network of sensors) is certainly the infrastructure complexity. UPGRADE’s approaches state that only 4 RnS repeaters are needed for a whole building, even if it has few floors. So we experimentally implemented a configuration with 3 repeaters and tested the propagation path through walls and ceilings. Another important feature is the actual geographical repartition of the repeaters. Many trials have confirmed that with our current resolution method (classical linearisation approach) there is the need to stay inside the rectangle defined by the outermost repeaters to converge to an acceptable location. Basically, comparisons are made on the basis of the resulting achievable accuracy of the computed location (typical final accuracy remains within the 1 to 2 meter goal). The last experiments we carried out concern the evaluation of the impact of motion in the resulting computed location. As a matter of fact, the time required ION GNSS 17th International Technical Meeting of the to cycle the 3 or 4 repeaters leads to a drift in the mobile terminal from one repeater to another. In other words, the location of the indoor receiver, when receiving signals from repeater “j”, is no longer the one it had when it received signals from the preceding repeater number “i”. This point is of importance since we are dealing with location accuracy. Both experimental results and extrapolation are discussed, showing the relationship between the speed of motion of the indoor receiver and the resulting accuracy (using the total cycling time as a variable).
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1959 - 1969
Cite this article:	Caratori, Julien, Francois, Marc, Samama, Nel, Vervisch-Picois, Alexandre, "UPGRADE RnS Indoor Positioning System in an Office Building," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1959-1969.
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