A threat to GNSS receivers is posed by a spoofing transmitter that emulates authentic signals but with randomized code phase and Doppler values over a small range. Such spoofing signals can result in large navigational solution errors that are passed onto the unsuspecting user with potentially dire consequences. An effective spoofing detection technique is developed in this paper, based on signal power measurements and that can be readily applied to present consumer grade GNSS receivers with minimal firmware changes. An extensive statistical analysis is carried out based on formulating a multihypothesis detection problem. Expressions are developed to devise a set of thresholds required for signal detection and identification. The detection processing methods developed are further manipulated to exploit incidental antenna motion arising from user interaction with a GNSS handheld receiver to further enhance the detection performance of the proposed algorithm. The statistical analysis supports the effectiveness of the proposed spoofing detection technique under various multipath conditions. 1. Introduction The received GNSS signal power at the output of a 3？dB gain hemispherical linearly polarized antenna at ground level is approximately ？130？dBm [1]. This makes GNSS receivers susceptible to nearby noise jammers and standoff spoofers (SS) that can easily transmit power levels well above ？130？dBm. A high processing gain based on a long integration time is often the only option available to overcome a noise jammer. Nevertheless, if the GNSS receiver undergoes random motion, then the channel decorrelates quickly such that attaining such large processing gains to overcome jamming is neither feasible nor desirable from an operational perspective. Also a jammer is relatively easy to locate with radio direction finding and to potentially disable as its spectrum is significantly larger than the ambient noise [2, 3]. In addition, the noise jammer is at least detectable as the spectral power in the affected GNSS receiver band will be abnormally high. Hence the jammer can deny service but the user is aware of being jammed, limiting the damage potential of the jammer. A more insidious threat is the standoff spoofer that broadcasts a set of replicas of the authentic satellite vehicle (SV) signals visible to the mobile GNSS receiver [2]. Disruption of GNSS services is achieved by randomly modulating the code phase over a small region of the overall Code Delay Space (CDS) that is commensurate with a target area. The spoofing attack is assumed to happen during the
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