GPS interference mitigation; Overview and experimental results

Abstract

GPS systems are proliferating, particularly in aviation where the FAA has decided it can be used for en-route navigation and CAT 1 non-precision landing approaches. The relatively low interference power levels that can jam GPS receivers necessitates the need to improve the system against either intentional or unintentional interferences. A number of methods may be used to do so. At a signal input level, the use of adaptive A/D convertors may be used to prevent the digital receivers saturating. Next, adaptive filtering techniques using either single or multiple element antennae coupled with both spatial and temporal digital processors can be used to reject both narrrowband and broadband interferences. Also other digital signal processing algorithms can be used to reject specific interferences from a spread spectrum system. Finally at a systems level both GPS and INS receivers may be tightly or loosely coupled to improve the accuracy and robustness of GPS in the presence of jamming signals. The advantages and disadvantages of various generic implementations of the above methods are reviewed and compared. The state of the art in implementing some selected methods will be reviewed and some experimental and simulation results presented to illustrate key issues. An advantage of digital beamforming is that interference direction of arrival information may readily be obtained from the antenna arrays. Algorithms can be readily borrowed from the sonar and radar fields to both calibrate such antenna and to estimate interference location.