Controlling the Galileo L1 OS Signal Emissions with Satellite Baseband Filters

Anthony R. Pratt and John I. R. Owen

Abstract:	Navigation satellites have a complex series of spectral emission requirement to meet. These range from controlling outof- band energy to protect sensitive services, such as the radio astronomy band at approximately 1612MHz, just above the L1 RNSS frequencies, to controlling in-band emission profiles to prevent harmful interference between one signal and another. Whilst the out-of-band emissions can be controlled through the output filters connected between the high power amplifiers (HPA’s) and antenna, this is not possible for spectral shaping within the transmission band. The technical challenge is increased by the need to transmit many signals within the same band, each carrying a different service. The current Galileo L1 signal proposals are a typical example, whereby 5 signals might be transmitted. These are PRS, BOC(1,1) and pilot OS component, and BCS([s];1) and pilot OS component. A similar situation is also likely to arise in the proposals for GPS3 whereby the signals could be CA code, P(Y), M-code, L1C and pilot signal. The method by which the signals are multiplexed onto the carrier also has a significant effect on the options for spectral control. Galileo will use a modified Interplex scheme to maintain a constant magnitude signal. The paper examines the various options for baseband spectral control through digital filters and proposes some practical options. One characteristic of such filters is the growth in the number of points in the output phase constellation. This growth poses real problems in the satellite payload design due to the precision of the amplitude control of the in-phase and quadrature carrier components. Examples are given showing that even a 2 pole filter may generate as many as 50 or more phase constellation states. The main body of the paper is concerned with the control and separation of the spectral from different services and signals. The filter method is shown to be more effective than other options (such as multi-level signal waveforms).
Published in:	Proceedings of IEEE/ION PLANS 2006 April 25 - 27, 2006 Loews Coronado Resort Hotel San Diego, CA
Pages:	865 - 875
Cite this article:	Pratt, Anthony R., Owen, John I. R., "Controlling the Galileo L1 OS Signal Emissions with Satellite Baseband Filters," Proceedings of IEEE/ION PLANS 2006, San Diego, CA, April 2006, pp. 865-875. https://doi.org/10.1109/PLANS.2006.1650686
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