A Software Simulation Tool for GNSS2 BOC Signals Analysis

L. Ries, L. Lestarquit, E. Armengou-Miret, F. Legrand, W. Vigneau, C. Bourga, P. Erhard and JL. Issler

Abstract:	Several BOC(n,m) signals are planned for future GNSS systems, with integer reference values of n and m, including BOC(10,5) for the GPS M-code, BOC(2,2) for the baseline open GALILEO signal, flexible BOC(n,m) for Galileo’s PRS signal and possibly an alternative BOC(a,b) for GALILEO in the E5 bands (E5a/L5 and E5b). The values of a and b are released in the paper. A BOC signal is formed in base-band by the product of two signal components : first, a non filtered Pseudo- random Noise (PN) code having a chip rate, Rc, and two possible values : -1 or 1, then a sub-carrier, either a non filtered square signal, or a sine signal, having a frequency, Rsc, equal or higher than Rc. A BOC(n,m) signal is such as n = Rsc/Rca and m = Rc/Rca ; n & m are not necessarily integers. We note Rca the GPS C/A code chip rate : 1.023 Mcps. The effect of the square sub-carrier is to split the main lobe of the PN code spectrum into two lobes centered at +/- Rsc from the central frequency. The BOC expansion ratio, a, is defined by a = n/m. When n & m are integers and n = m, the associated BOC(n,n) is a Manchester code. An Alternative-BOC (ALTBOC) signal is a BOC-like signal having different PN codes in the lower and the upper main split lobes. Alternative-BOCs allow one signal service per lobe. If the 2 PN codes of an alternative-BOC are made identical, the signal becomes a « classical » BOC. CNES suggested a mean of generating an alternative BOC, with 4 different codes, while keeping the signal’s envelope constant. In order to closely study the BOC signals, in particular those here above, as well as to provide its partner in the GALILEO program with valuable expertise, CNES (the French Space Agency) has undertaken the development of software simulation tools of BOC signals, in cooperation with ESA ( The European Space Agency ). This tool comprises a highly flexible signal transmitter, capable of generating any BOC signal (n and m variable, parametric code length and data rate) and alternative BOC. ( NB : Internal work about the alternative BOC has also been performed in CNES, ESA and GAIN ). The tool includes simulation of payload’s effects (e.g. distorsions). It includes also the definition of several kinds of receiver architectures and perturbations like interference, multipath, and dynamics. This tool is aimed at studying the acquisition strategies, the tracking performances in the presence of thermal noise, interference and multipath. The effect of parameters n and m on the performances are being investigated, as well as the impact of alternative BOC both on the receiver’s architecture and capabilities, but also on the payload. The tool shows to be is a valuable asset to investigate the best compromises for defining a good reference receiver for BOC signal. These reference receivers are then used to compare the influence of parameters n and m as well as different scenarii for future GNSS systems. The paper describes the hypothesis of those simulations including the non-linear distorsions model, as well as the most interesting results and some recommendations on the E5 band signals. The results provided in the paper come from ESA and CNES internal investigations on the Alternative-BOC Modulation, and from M3System and Alcatel Space studies on the subject ( BOC and ALTBOC signals ).
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2225 - 2239
Cite this article:	Ries, L., Lestarquit, L., Armengou-Miret, E., Legrand, F., Vigneau, W., Bourga, C., Erhard, P., Issler, JL., "A Software Simulation Tool for GNSS2 BOC Signals Analysis," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2225-2239.
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