New Open GNSS Signals: First Combined GPS/GLONASS/GIOVE Experiments

C. Boulanger, B. Bonhoure, N. Suard, D. Lapeyre

Abstract:	Currently, positioning is widely done with GPS L1C/A or with L1P-L2P dual frequency combination with very good performances. The restoring of GLONASS has increased interest for multi system applications. In the continuity, with the modernisation of GPS and GLONASS and the deployment of GALILEO, COMPASS... a wide number of additional signal combinations will be possible in a very near future and three of them are of particular interest for open service users: -First one is the mono frequency L1 based on a three constellation combination, GPS, GLONASS, and GALILEO, the COMPASS signal interface being not yet published. This configuration is very attractive in constrained environments. -Second one is made with two signals transmitted by two interoperable constellations: L1C/A-L5 on GPS and E1BC-E5a on GALILEO. This bi-frequency combination allowing ionosphere delay correction is likely to be used for precise or Safety of Life applications in future. -Third one is the L1C/A – L2C combination Within the framework of GPS modernisation, L1P and L2P GPS signals which can be used by civilian receivers with codeless or semi-codeless signals processing, will be denied in 2020. Non-military users will then be obliged to switch to the new open signals. The L1C/A-L2C couple of frequencies, shared by GPS and GLONASS is interesting and seems to be the most natural evolution. However L1 and L5 are in ARNS bandwidths and will be used in the next generation SBAS standard. During spring 2011 only one satellite having the L5 capability is operational but with the launches of GPS II-F at the same time as GALILEO deployment, the number of available satellites will increase very quickly. Of course many others configurations can be considered but with a degraded trade-off between complexity and performances and even if these “future” configurations can be fully exploited only by a few years, they can already be tested: For the L1 tri constellation combination, 23 GLONASS satellites are declared operational in addition to the 31 GPS and the 2 GIOVE. On GPS side, two satellites were transmitting on the L5 frequency in 2010: the II-RM satellite, SVN-49 (PRN 01) carrying a demonstration payload for L5 and the SVN-62 (PRN 25) carrying the nominal II-F generation payload. Noting that SVN-49 status was unhealthy, it could be used for experimental purpose by forcing its use in experimental/test facilities. On GALILEO side, the two GIOVE prototype satellites transmit representative E1BC and E5 signals (or E1-E6) and thanks to an agreement between CNES and ESA, we have access to the ground navigation messages. In 2010 there were short periods when these four satellites were simultaneously visible and so a full civilian L1/L5 position could be computed, as for example on the 21st of August 2010. Concerning the user segment, receiver manufacturers have already designed equipment (receiver, antenna…) to track satellites from multi constellations on quasi all available signals. Last year, we have acquired a commercial multi constellation receiver Asterx3 (Septentrio). With a prototype firmware we can track 12 GPS on all signals, the 2 GIOVE prototypes on E1BC-E5a,b and 9 GLONASS on L1C/A-L2C/A and generate RINEX3 files. In addition, in the frame of a CNES contract, Thales Services SAS has developed a tool, ADN (for Analysis and Display of Navigation data), able to use all the signals and messages emitted by the GPS, GLONASS and GALILEO/GIOVE constellations. This software is able, among other possibilities, to process RINEX files to compute GNSS positions in various modes and to include external biases. Considering the new possibilities offered by the 3 systems and based on COTS receivers used as data recorder, this article will aim at describing the experimental PVT computed with sets of real data in the advanced configurations introduced before. In dual frequency, when the considered signals are different from those used by the ground segment to compute the satellite ephemeris and clock, Inter Signal Corrections (ISC) have to be taken into account in addition to the Time Group Delay (All the definitions and equations are detailed in the GPS ICD-200E, ref [5]). For GPS, these correction parameters will be broadcast in the CNAV message in the future but for L1C/A and L2C they are already available in IGS products. On the opposite for the GPS L5 signal, no information is available until now and the ISCL5 has to be calculated. For the signal combinations presented above, early results show good positioning performances within a few meter accuracy.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2821 - 2828
Cite this article:	Boulanger, C., Bonhoure, B., Suard, N., Lapeyre, D., "New Open GNSS Signals: First Combined GPS/GLONASS/GIOVE Experiments," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2821-2828.
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