Simulation of Swept FM Interference and its Impact on an Aviation Receiver

M. Brenner

Abstract:	GPS jammers used to prevent tracking of cars and trucks have been identified as a potential problem for future GPS aviation applications. So far both GBAS and SBAS stations have been affected and the consequences have been described in recent papers. These jammers are low cost devices that based on simple circuitry generate a swept FM signal in the GPS band. Such jammers are considered broadband interferers and a white noise approximation is often used to model their impact on a GPS receiver. The FAA is currently sponsoring research related to the proposed GBAS standard for precision approach down to CAT III weather minima referred to as GBAS approach service type D (GAST D). In an effort to gain a better understanding of the swept FM jammer signal impact on a GBAS ground station used for safety critical operation such as a CAT IIIb weather minimum landing, Honeywell has developed an aviation receiver simulation model that covers everything from front end filtering and analog to digital conversion to tracking and signal quality monitoring. The simulation provides a time resolution of 1 nanosecond when modeling the incoming signals and sampling rates in the range 20 - 100 MHz are possible. One of the questions the simulation is slated to answer is to what extent and under what conditions the white noise model of the swept FM jammer signal is a valid approximation. In a safety critical system it is essential that the ranging error is bounded at all times and the simulation is used to test the validity of the bounding under various scenarios and assumptions. The paper gives an overview of the simulation capabilities and provides illustrations of how different jammers would impact an aviation receiver in terms of pseudo range and carrier errors as well as signal quality measures such as signal to noise ratio, bit errors, parity errors and cycle slips. The paper also looks at the swept FM jammer from a spectral standpoint to explain why further validation of the white noise approximation is desirable. It then looks at error bounding for different jammer chirp rates by simulating jammer exposure over time frames of the order of minutes and presents the results relative to white noise predictions in cumulative distributions.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	1359 - 1370
Cite this article:	Brenner, M., "Simulation of Swept FM Interference and its Impact on an Aviation Receiver," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1359-1370.
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