Potential Interference Sources to GPS and Solutions Appropriate for Applications to Civil Aviation

R. Johannessen, S. J. Gale, M. J. A. Asbury

Abstract:	When GPS is subjected to interference the system performance gradually deteriorates as the interfering levels increase. Two modes of interference are discussed in detail, namely that arising from transmissions at frequencies close to the GPS frequencies and transmissions with a harmonic in the GPS band. It is argued that the former requires RF filtering in the receiver with a quality better than generally specified. The latter cannot be dealt with in such a way. The paper reports on measurements carried out on the harmonic levels transmitted by one UK TV transmitter and several hundred aircraft VHF transmitters. These measurements show there is a measurable level of harmonics in the GPS band. The UK TV transmitter does not however represent a threat to aviation unless the aircraft is so close as to represent a physical danger. The probability that one aircraft's VHF transmitter will interfere with the GPS receiver on an other aircraft is tolerably small, but there is a significant probability that a GPS receiver can suffer when there is a VHF transmission from the same aircraft. The paper makes several recommendations including suggested international effort to ensure spurious emissions are both quantified, and kept at a level significantly lower than that achieved today.
Published in:	Proceedings of the 45th Annual Meeting of The Institute of Navigation (1989) June 27 - 29, 1989 Alexandria, VA
Pages:	195 - 201
Cite this article:	Johannessen, R., Gale, S. J., Asbury, M. J. A., "Potential Interference Sources to GPS and Solutions Appropriate for Applications to Civil Aviation," Proceedings of the 45th Annual Meeting of The Institute of Navigation (1989), Alexandria, VA, June 1989, pp. 195-201.
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