Signal Choice for Galileo Compared Performances of Two Candidate Signals

Laurent Lestarquit and Pierre-Alexis Brison

Abstract:	A choice shall be made for the GALILEO signal for Open Acces Service (OAS), based on the performances of candidate signals. The declared bandwidth available for this signal is 4 MHz wide at the most. Therefore when assessing the performances of the GALILEO system, this bandwidth limitation shall be taken into account. Two main signal structures are currently proposed in Europe among others. The first one is a signal cadenced at 3 Mchip per seconds and filtered with a Square Raised Cosine (SRC) filter so as to limit its spectral occupancy to 4 MHz. The second candidate is a standard C/A code at 1.023 MHz, but filtered at the payload with a 4 MHz n the order butterworth filter. The performances of both signals are compared with regards to multipath effect mitigation, which is the main error source for a dual frequency system. With standard ½ chip spacing correlator, the 3 Mchip/s rate signal has better performances, but this is not the case when advanced correlators are used. For this later signal, the use of narrow correlators and of the Double Delta Correlator (DDC) based on 5 evenly spaced correlators doesn’t improve the multipath mitigation. This is because with SRC filtering, only a part of the main lobe of the signal is transmited. On the oher hand, with the standard C/A 1.023 Mchip/s rate code the use of advanced correlators improves the multipath rejection. This is because at least the first secondary lobe is transmitted. Results show that for most multipaths the GPS signal is more robust to multipath when the DDC is used. With short multipath, the 3 Mchip/s signal is not as good as the GPS signal. The conclusion is that the 3 Mchip/s signal doesn’t offer a clear advantage over the standard C/A code, even when filtered in a 4 MHz bandwidth. Moreover, if backward compability, or signal interoperability with GPS is to be taken into account, a GPS like signal shall be recommended for GALILEO.
Published in:	Proceedings of the 2000 National Technical Meeting of The Institute of Navigation January 26 - 28, 2000 Pacific Hotel Disneyland Anaheim, CA
Pages:	175 - 180
Cite this article:	Lestarquit, Laurent, Brison, Pierre-Alexis, "Signal Choice for Galileo Compared Performances of Two Candidate Signals," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 175-180.
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