GPS World, September 2010

foliage attenuation and therefore the SV signal bearing is random with significant variations As we discuss here effective spoofing detection is still possible for a single antenna GNSS receiver based on the differing spatial correlation of the spoofing and authentic signals in the proximity of the receiver antenna The basic assumption is that the antenna will be spatially moved while collecting GNSS signal snapshots Hence the moving antenna generates a signal snapshot output similar to that of a synthetic array SA which under some additional constraints can provide an effective means of detecting the source of the GNSS signals from a spoofing jammer or from an authentic set of SVs We assume here an arbitrary antenna trajectory with the spoofing and authentic signals subjected to random spatial multipath fading The processing will be based on exploiting the difference in the spatial correlation of the spoofing and the authentic signals Spoofing Detection Principle Consider a GNSS handset receiver FIGURE 1 consisting of a single antenna that is spatially translated in time along an arbitrary trajectory as the signal is processed by the GNSS receiver There are L authentic GNSS SV signals visible to the receiver along with a jammer source that transmits spoofi ng replicas of the same L authentic signals It is assumed that the number of spoofed signals range from 1 to L which are coordinated such that they correspond to a realistic navigation solution at the output of the receiver processing The code delay and Doppler associated with the spoofing signals will typically be different than those of the authentic signal The basic technique of coordinated spoofing jamming is to present the receiver with a set of L signals that appear to be sufficiently authentic such that the spoofing and authentic signal sets are indistinguishable Then the spoofing signals separate slowly in terms of code delay and Doppler such that the navigation solution corresponding to the L spoofing signals will pull away from the authentic navigation solution The focus herein is on methods where the authenticity of the L tracked GNSS signals can be tested directly by the standalone receiver and then selected for the navigation processing This is in contrast with other methods where the received signals are Security RECEIVER DESIGN transmitted back to a communication command center for verification of authenticity The consideration here is on the binary detection problem of assessing if each of the 2L potential signals is authentic or generated by a spoofing source This decision is based on observations of the GSG 54 GPS 8 CHANNEL SIMULATOR GPS Constellation in a Box Eight Channel GPS Test Device for Manufacturing and Development Applications user movements Synchronizing Critical Operations 15853215800 North America sales@ spectracomcorp com Test Measurement by Spectracom 46 8 598 510 00 Europe www spectracomcorp com www gpsworld com September 2010 GPS World 29