Dual Use of Military Anti- Jam GPS Receiver Design Techniques for Commercial Aviation RF Interference Integrity Monitoring

Phillip Ward

Abstract:	There have been numerous papers published on GPS integrity monitoring from the perspective of detect- ing and reporting space segment failures. Another im- portant aspect of GPS integrity monitoring that has received less attention is the monitoring of radio fre- quency (RF) interference which can result in degraded accuracy performance or complete loss of receiver tracking. The RF interference source can be friendly or intentional and may be predictable or unpredictable. For military applications, intentional jamming is expected. Therefore, military GPS receivers are usually designed to be robust under severe jamming threats. Commercial GPS receivers seldom have built-in design provisions to either monitor or minimize the effects of RF interference, but this may become an important requirement for com- mercial aviation. The effect of RF interference is reduced carrier to noise power density ratio, C/No. When C/No is reduced below the tracking threshold of a receiver, the GPS measurements are corrupted and the navigation func- tion can no longer operate reliably unless the system is augmented by an inertial measurement unit (which is immune to RF interference). P(Y) code is more robust than C/A code to RF interference. In addition, C/A code is vulnerable to continuous wave (CW) RF interference due to a leak- through phenomena that is described in the paper. This C/Acodevulnerability may become an additional source of RF interference problems for commercial aviation GPS receivers since Standard Positioning Service (SPS) GPS users will be denied access to P(Y) code when antispoofing is activated. This paper describes RF interference measurement techniques for the purpose of GPS integrity monitoring. It also describes several GPS receiver and antenna design techniques which can add tracking robustness when C/No is reduced by RF interference. These dual- use techniques should be considered if RF interference becomes a source of GPS signal integrity problems for commercial avionics applications.
Published in:	Proceedings of the 50th Annual Meeting of The Institute of Navigation (1994) June 6 - 8, 1994 Antlers Doubletree Hotel Colorado Springs, CO
Pages:	41 - 54
Cite this article:	Ward, Phillip, "Dual Use of Military Anti- Jam GPS Receiver Design Techniques for Commercial Aviation RF Interference Integrity Monitoring," Proceedings of the 50th Annual Meeting of The Institute of Navigation (1994), Colorado Springs, CO, June 1994, pp. 41-54.
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