Galileo Consumer Receiver: Live Satellites at Last

P.G. Mattos, F. Pisoni

Abstract:	Galileo has been on the horizon for some years, and ST receiver development started in 2005 with the GR-Poster project for a Galileo-Ready Receiver which was demonstrated in 2007 in FPGA with signals from a simulator. With the public ICD released in 2008, well in advance of the signals, Galileo capability was incorporated in the silicon for the chips used in Satnavs/PNDs from 2009, meaning many millions of these devices in the field are Galileo capable with just a software upgrade. The Galileo test satellites (GIOVE-A and B) did not transmit the standard signal, so were useful for infrastructure development, but not for consumer receiver testing. Specifically they used non-standard spreading-code lengths, not in the same family as GPS Gold-codes, and twice the length of the production Galileo satellites as specified in the ICD. As a result existing silicon could not support them, not on the hardware code generators nor on the memory code generators, and research could only be done by capturing the signals and processing them in software emulator of the receiver. That did not prevent research continuing in the background, and a second generation of Galileo capable GNSS chips, Teseo-2, was produced. It was sold in volume as a multi-constellation GNSS chip, but in practice only used GPS and Glonass in the field, waiting for the Galileo satellites to appear. In late 2011, the first two IOV satellites were launched, and in late 2012 IOV3 and 4, with their orbits chosen such that as a group of four they could support positioning for one or two hours a day. As these 4 satellites transmitted the real ICD signals, consumer receiver silicon could burst into life. In December 2012, while the IOV satellites were being commissioned, the full Teseo-2 consumer receiver acquired and tracked all 4 simultaneously for the first time, but they could not be used for positioning yet as the data packets were not populated. Full receiver operation to PVT was only possible with signals from the simulator. In mid January 2013 the first two IOV satellites transmitted ephemeris data temporarily, and first attempts were made to position using them in conjunction with GPS in a multiconstellation solution, though there were no guarantees on the data, as it was marked unhealthy. These tests will be continued whenever possible, whenever live data is seen on the satellites as part of the satellite’s own testing. A critical part of the transmitted data that determines the receiver test strategy is the availability and precision of the GGTO parameter, which reports the difference between Galileo and GPS system time. Without this parameter, either a minimum of two Galileo satellites are needed in the mixed constellation, or alternatively the parameter must be estimated in the receiver when there is an accurate GPS fix, and then held constant for subsequent mixed fixes. While the Galileo constellation is so small, it is very difficult for the control segment to accurately determine both the orbits and the GGTO, so it is not expected to be immediately available or accurate, though laser-ranging may be used to bootstrap the system. It is anticipated that full healthy data from all four satellites will be transmitted from the end of Q2/2013, allowing the first true Galileo positioning to be demonstrated for a short time each day, and its use in multi-constellation fixes for a significant percentage of the time. This will allow tests to be conducted to generate the appropriate results for the full paper. Galileo signals have several differences from legacy GPS, such as BOC modulation, a pilot signal with secondary code, convolutional coding/Viterbi decoding for error correction etc. Comparisons will be made between the signals in real world tests in urban canyons and light indoor scenarios, mobile as well as static. The BOC modulation sharpens the correlation peak, allowing tighter tracking in a benign environment, while it also widens the bandwidth, reducing the effect of local reflections and multipath. The pilot signal allows tracking with much longer coherent integration time, as there are no unknown data bits, while its secondary code allows continuous confirmation that the signal is real and not a jammer or a cross-correlation. The convolutional coding enables error-free downloading in marginal scenarios of either attenuation or momentary obstructions. Having a full Galileo receiver that can also receive GPS for comparison will allow the individual benefits of each signal improvement in each scenario to be studied. The full paper will report the initial testing of the receiver from Q2/2013 and also the full testing with healthy signals in Q3. It will concentrate on the characteristics of the Galileo signal in the consumer and automotive environment, its acquisition, tracking and positioning as a standalone constellation, in comparison with a GPS-only receiver, rather than its use as a component of a multiconstellation receiver, which is reported in another 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:	1457 - 1460
Cite this article:	Mattos, P.G., Pisoni, F., "Galileo Consumer Receiver: Live Satellites at Last," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1457-1460.
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