GPS Antijam via Subspace Projection: A Performance Analysis for FM Interference in the C/A Code

This paper is concerned with frequency modulated (FM) interference cancelation in GPS receivers. FM signals are instantaneously narrowband and have clear time–frequency signatures that are distinct from the GPS C/A spreading codes. Interference cancelation is performed by first constructing the interference subspace and then projecting the data onto the orthogonal subspace. Interference subspace estimation can be provided by the time–frequency distribution (TFD) or any other instantaneous frequency (IF) estimator. The GPS receiver signal-to-interference and noise ratio in the presence of IF or phase estimation errors is derived. The errors are assumed Gaussian and independent. From both analysis and simulations, it is shown that phase estimation errors can substantially impede interference rejection in GPS using subspace projection techniques.