A method is developed to detect GNSS spoofing by processing beat carrier-phase measurements from a pair of antennas in a CDGPS-type calculation. This system detects spoofing attacks that are resistant to standard RAIM technique, and it can sense an attack in a fraction of a second without external aiding. The signal-in-space properties used to detect spoofing are the relationships of the signal arrival directions to the vector that points from one antenna to the other. In the un-spoofed case, there are a multiplicity of relationships between the inter-antenna vector and the arrival directions of the multiple signals, which results in a quantifiable multiplicity of carrier-phase single-differences between the antennas. In the spoofed case, there is a single direction of arrival, assuming a single spoofer transmission antenna, and the carrier phase single-differences are identical for all channels, up to an integer cycle ambiguity. A real-time implementation of this detection method has been developed, and it has been tested against live-signal spoofing attacks aboard a superyacht that was cruising around Italy en route from Monaco to Venice. The prototype system demonstrated an ability to detect spoofing attacks in a fraction of a second, though lags in the system’s signal processing lengthened the detection delay to as much as 6 seconds. The system experienced challenges during the initial phase of a spoofing attack if the spoofer power was not much greater than that of the true signal. The true and spoofed signals interfere in a beating pattern in this case, making the composite signal harder to track and harder to classify as being either spoofed or non-spoofed. After the spoofer drags the victim receiver off to an erroneous position or timing fix, the beating subsides, and the new spoofing detection system performs well.

Cite and download the paper:
M.L. Psiaki, B.W. O'Hanlon, S.P. Powell, J.A. Bhatti, K.D. Wesson, T.E. Humphreys, A. Schofield, "GNSS Spoofing Detection using Two-Antenna Differential Carrier Phase," ION GNSS+, Tampa, FL, September 2014.

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