A new approach for decimeter accurate GNSS indoor positioning using carrier phase measurements

In order to improve the potential accuracy of our indoor positioning system, previously based on repeaters, we have moved for a few years to the so called 'repealite system'. The main idea is to be able to carry out carrier phase measurements: one knows that these Doppler based values are usually much more accurate and less sensitive to multipath than code based approaches. Thus, the current system is based on transmitters that broadcast a single signal, just time shifted from one 'repealite' to the next in order to avoid intentional interference. The present paper copes mainly with carrier phase measurements and proposes new ways of resolving ambiguities. The two main techniques are based respectively on the elimination of 'non-possible' combinations of phase ambiguities from various transmitters and the direct calculation of the ambiguity value from transmitters. The first method is quite classical when the second is original, but both are helped by the reduced size of the considered environment. In addition, the paper shows the beneficial effect of redundancy in the measurements, provided by an increased in the number of transmitters (note that only 2D positioning is considered with either 3 or 4 transmitters). In addition, these two techniques are implemented and experimental results are available in a real harsh environment (a classroom with metallic walls and many windows). A comparison is given for the two approaches and benchmark carried out with respect to the real locations. The main goal being to obtained the more accurate 'absolute' positioning, while one knows that relative positioning using carrier phase measurements can easily reach the decimeter accuracy in quite good environments. Obtained accuracy values are in the 10 to 50 centimeters, depending on both the technique and the real experimental conditions.