First GNSS Positioning using IOV Galileo Satellites

B. Bonhoure, C. Boulanger, T. Chapuis, F.X. Marmet, N. Suard

Abstract:	With 30 operational satellites, the GPS system is an excellent mean to determine one’s position or time. GPS has become quite strategic today and similar systems will emerge in the coming years, like GALILEO for Europe or BEIDOU for China. The GLONASS constellation is also being completed and improved, and can be used today with GPS. Augmentation systems like WAAS and EGNOS may also provide usable range measurements. The future is GNSS, i.e. the major part of receivers is likely to receive and combine signals from several systems. This will permit improvement of performances, in particular in constrained environments, and also will offer operational back-up or independence in case of failure or unavailability of one system. An important agreement was signed in 2007 between USA and Europe for GPS/GALILEO compatibility and interoperability. With the successful launch of the four In Orbit Validation GALILEO satellites in 2011 and 2012, and reception of first signals on ground, it is now possible to combine GALILEO and GPS measurements for positioning, or even get a position from only GALILEO satellites. Mixed GPS/GIOVE PVTs have been successfully calculated over the last years by CNES, for static and dynamic receivers. A realistic approach was followed for the extrapolation of GIOVE Broadcast with an extrapolation time of 2 hours close to the 100 minute requirement for GALILEO. Results were presented and published for ION GNSS 2010 & 2011, and showed a pseudo-range accuracy of the same order for GPS & GIOVE satellites. IOV GALILEO satellites can now be used instead of GIOVE satellites. This paper will very briefly remind theoretical approach and will more focus on practical results including Key Parameter Indicators (KPI) like 95% accuracies or pseudo-range residuals, over long enough periods. Global Navigation Satellite Systems positioning is based on the synchronization of emitting satellites to a common reference time. With at least 4 synchronized satellites, the receiver can calculate the four usual unknowns: the 3D position and the delay between receiver and system time. So, in order to combine measurements from different satellite systems like GPS and GALILEO, the bias between the different system times shall be broadcast, or determined at the user level as additional unknowns. In fact, Galileo and future GPS satellites will transmit the time delay between both systems, which is called GGTO - Galileo to GPS Time Offset. This way, receiver measurements - called pseudo-ranges - can be combined directly to calculate the position and time offset of receiver. Results will be presented for different types of receivers, in different environments i.e. static/dynamic and open/constrained, and for single and dual frequency measurements i.e. for key configurations like L1 and L1/L5 in the future thanks to the fact that GALILEO IOV signals are received today by different types of receivers, including commercial receivers like Trimble NetR9, JAVAD Delta, LEICA GR10, Septentrio PolaRx4, Novatel OEM6…, some of them being deployed by CNES in its GNSS network and included in the IGS MGEX (Multi-GNSS Experiment) initiative. Some prototype receivers like Septentrio GeneRx and TURN - used for GIOVE/GALILEO validation by ESA – can also be used. As for GPS/GIOVE mixed PVTs, base-line is to use the GALILEO Broadcast ephemerides generated on ground by ESA. This information can be accessed thanks to an agreement between CNES and ESA. Since the GALILEO system is being deployed, Broadcast ephemerides from satellites may be not available or as accurate as for the future operational phase. First Broadcast ephemerides have been sent from real GALILEO in January 2013 during a test, but were not accurate as foreseen in routine, as shown in comparison with precise ephemerides calculated in the IGS MGEX campaign. If real GALILEO ephemerides sent from satellites are accurate enough within the coming months, they will be used for the paper. At the end of December 2012, first successful GALILEO only and GPS/GALILEO PVTs in mono and dual frequency mode have been processed by CNES, using ESA ground ephemerides. GALILEO only PVTs show already an accuracy of a few meters for positioning when there is good geometry, around 5% of time every 1.5 days for a given position, i.e. with HDOP from 2 to 4. Results show a iono-free range accuracy of around 1 meter for GALILEO and GPS satellites. Those good results will be consolidated over the coming months and presented in the paper.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	1480 - 1491
Cite this article:	Bonhoure, B., Boulanger, C., Chapuis, T., Marmet, F.X., Suard, N., "First GNSS Positioning using IOV Galileo Satellites," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1480-1491.
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