Robust Time Transfer from Space to Backup GPS

D. Whelan, P. Enge, G. Gutt

Abstract:	This paper describes the ongoing development of two space-based systems to transfer time when GPS is unavailable due to radio frequency interference (RFI). The first is based on controlled radiation pattern antennas (CRPAs) in conjunction with the geostationary satellites used by Space Based Augmentation Systems (SBAS). In this case, the sought-after processing gain derives from three factors: attenuation of the interfering signal by the CRPA; increased spread spectrum processing gain by the use of L5 rather than the C/A code; and reduced tracking bandwidths. The second system is based on the use of the low earth orbiting satellites from the Iridium constellation. In this case, a processing gain of approximately 27 dB derives from the increased signal strength from satellites with an 850 km altitude rather than the 20,190 km altitude of the GPS satellites. In addition, CRPAs can be used to further increase the processing gain of the Iridium satellites. The paper describes both concepts and includes preliminary performance results. It also describes an application of near term interest: time transfer between terrestrial ranging sources used to provide alternative position navigation and time (APNT) to civil aviation.
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	907 - 914
Cite this article:	Whelan, D., Enge, P., Gutt, G., "Robust Time Transfer from Space to Backup GPS," Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010, pp. 907-914.
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