GNSS jamming mitigation using adaptive-partitioned subspace projection technique

Intentional jammers broadcasting chirp-style signals present a major threat to the operation of the global navigation satellite systems (GNSS) receivers. The time-frequency (TF) domain method based on the subspace projection technique is a common countermeasure against jamming. However, it is sensitive to inaccuracies in the instantaneous frequency (IF) estimates when dealing with jammers with rapidly changing frequency characteristics. In this paper, an approach for chirp-style jamming signal suppression in GNSS receivers using an adaptive-partitioned subspace projection is developed, which is insensitive to IF estimation errors. We first propose to choose the TF observation window length based on the jammer sweep rate and displace the IF estimates by a spectral bin to handle the resolution errors in the IF estimates. This operation ensures that the instantaneous phase (IP) estimation errors approximately stay constant for the interval that the jammer IF varies linearly upward. Owing to this property, the received data vector is partitioned into adaptive block sizes based on the jammer chirp rate estimates, which reflect the varying IF characteristics. The received signal is then projected onto the jammer orthogonal subspace constructed from the IF estimates according to the adaptive projection blocks. Simulation results indicate the effectiveness of the proposed technique for suppressing chirp-style jammers when compared with other techniques reported in the literature. The proposed approach provides an improvement by up to 11 dB in terms of the correlator signal-to-noise power ratio of the processed signal.