Impact of the Spreading Codes onto the S-Curve Bias for the Galileo E5 Signals

F. Soualle

Abstract:	At a time when the first Galileo test and validation satellite is operational, the main characteristics of the Galileo signal structure are for most of them well specified. One of the possible final tasks deals with the application of shifts between the four spreading codes of the E5 signal, which are combined with a so-called Alt-BOC pulse modulation. For this purpose, the criterion that will be taken into account is the bias of the S-Curve characteristic used by the delay lock loop (DLL). It is namely shown in this paper that the S-curve bias (SCB) for a receiver tracking the E5 signals, can achieve several hundreds of picoseconds, if no shift between the four spreading codes for the E5a-I, E5a-Q, E5b-I and E5b-Q signal components is applied. Though this value is not critical for most GNSS applications, it might impact specific high performance applications. This paper, describes a method which determines appropriate shift values between the four E5 codes in order to reach SCB levels with an order of magnitude below the 50 ps. For this purpose, a non-coherent DLL using the single side band tracking option will be considered for all four code replicas. With these hypotheses, a cost function based onto the symmetry properties of the code crosscorrelation between the code replica and the different code components (including the codes used by the product signals of the Alt-BOC modulation) will be developed and integrated into a shift selection algorithm. The benefit of applying these shifts in term of reduction of the SCB will be described when considering correlation times equal either to the duration of the primary or of the secondary code period. It has to be mentioned that this study has been carried out in the frame of the Galileo program, under contract with ESA. Furthermore, and to avoid any confusion, the term Galileo used in this paper refers to a trademark of the European Commission. The space program Galileo is a joint initiative of the European Commission and the European Space Agency.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	1583 - 1594
Cite this article:	Soualle, F., "Impact of the Spreading Codes onto the S-Curve Bias for the Galileo E5 Signals," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 1583-1594.
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