Galileo Signal Optimisation In L1

Anthony R. Pratt and John I. R. Owen

Abstract:	Since the decision was made to change the baseline modulation for the Galileo open service on L1 to BOC(1,1) format, speculation has continued on the possibility of further optimisation. This has been driven, amongst other motivations, primarily by the desire to improve the multipath performance of the L1 open service. The paper reports the recent United Kingdom studies in seeking alternative but compatible modulation which might offer improved performance. It has become clear that the multi-path mitigation algorithms, upon which the equality of the various modulation options considered for L1 was, in part, based, may have a significant cost in terms of signal to noise ratio (see reference 1). This reference shows that it is the high frequency content of the modulation that makes most contribution to the effectiveness of multi-path mitigation algorithms. At this stage in Galileo’s signal development, the possibility remains to modify the baseline modulation in such a way as to improve the higher frequency content, thereby ensuring better performance from multi-path mitigation algorithms without any signal to noise penalty (such as narrow and strobe correlation). It has become clear that one additional modulation format which might not interfere significantly with other services on L1 is a BOC(5,1) as this is located in a null in BOC(10,5). This paper considers a number of options for mixing BOC(5,x) and BOC(1,1) modulation waveforms in a way which enhances multi-path mitigation processes in the receiver. The authors have accepted a number of constraints to the mixture process in order that the resulting modulation remains BPSK although there are other mixing techniques without this constraint. This may affect the inter-operability of GPS and Galileo. The paper also considers the receiver options and signal losses available to mass market and other classes of users that may not wish to use the full bandwidth of the signal, thereby only partially decoding the signal using a BOC(1,1) reception replica. Conclusions are drawn as to whether the proposed modulation options represent useful optimisation.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	332 - 345
Cite this article:	Pratt, Anthony R., Owen, John I. R., "Galileo Signal Optimisation In L1," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 332-345.
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