Methodologies for Assessing Intrasystem and Intersystem Interference to Satellite Navigation Systems

A. J. Van Dierendonck and Chris Hegarty

Abstract:	GPS intrasystem interference is defined as interference to the acquisition, tracking, and data demodulation of GPS and WAAS (or SBAS) signals by C/A, Y, and M code signals generated by GPS satellites and by C/A code signals generated by SBAS satellites. GPS intersystem interference is defined as interference from signals from another satellite navigation system such as Galileo. To date, the assessment of these interferences has generally been pessimistic, but under certain analysis conditions optimistic. This result is primarily attributable to the use of methodologies that are either too simplistic or even erroneous. This situation is further compounded by the fact that some of the signals, such as the GPS C/A code signals, are coded with relatively short repeating codes. Because the past and more simplistic assessment of intrasystem interference between the C/A code signals resulted in pessimistic and, in some cases, erroneous results, refined methodologies have been developed to assess C/A code intrasystem interference (sometimes called self-interference). This paper presents these refined methodologies, along with derivations, and applies them to realistic scenarios. These methodologies do not lose sight that the C/A codes produce line spectrums. However, they do account for the fact that the codes are modulated with navigation data that spread the lines over the data bandwidth. This is even more significant when addressing SBAS signals that essentially have 500-baud random symbols (because of the FEC encoding utilized in these 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:	1241 - 1250
Cite this article:	Van Dierendonck, A. J., Hegarty, Chris, "Methodologies for Assessing Intrasystem and Intersystem Interference to Satellite Navigation Systems," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1241-1250.
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