Document Type

Conference Proceeding

Date of Original Version

1-2013

Abstract

GPS spoofing is a hot topic of late; technical discussions vary widely based upon the assumed capabilities and a priori knowledge of the spoofer. For a single GPS receiver, various methods to detect a spoofing event have been proposed in the literature. These range from simple ideas (e.g. monitoring the power levels of the GPS signals) to more complex concepts (e.g. looking for vestigial peaks in the correlator outputs) to the comparison to non- GPS signals (e.g. an IMU). Much of this prior work has been on the conceptual level with limited experimentation; little appears to have been done to analyze the resulting detection performance. The detector of interest here monitors the GPS signals using not one, but two or more receivers with their antennas at known relative positions. The assumption is that during a spoofing event these multiple receivers will receive the same spoofer RF signal in that the satellites’ characteristics (i.e. relative times of arrival) are identical at all of the antennas. With no spoofer present, each antenna would receive a unique RF signal, consistent with its position in space. The concept of the detector, then, is that the presence of spoofing is discernible from the near equivalence of the receivers’ receptions. While one could compare these multiple receptions at the RF level, we compare the position solutions across receivers, declaring a spoofing event if the resulting position solutions are too close to each other as compared to the (known) relative locations of the antennas. The primary advantage of such an approach is that the hypothesis test does not require receiver hardware modification or even access to software GPS methods; a separate processor could easily monitor the positions output from the receivers. In this paper we analyze such a detector from a Neyman-Pearson perspective assuming Gaussian statistics on the position solution data. We consider four cases: (1) two receivers with fixed (known) locations, (2) two receivers with fixed separation and known orientation (but unknown absolute position), (3) two receivers with fixed separation and unknown orientation, and (4) a three receiver example.

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