GPS World, September 2010

PRN 15 16 18 21 22 15 1 088 092 092 093 16 088 1 09 09 088 18 092 09 1 093 092 21 093 09 093 1 093 22 092 088 092 093 1 ÅTABLE 1 Correlation coefficient determined for the set of spoofing signals PRN 5 15 16 18 21 5 1 03 02 04 03 15 03 1 05 01 04 16 02 05 1 00 06 18 04 01 00 1 03 21 03 04 06 03 1 ÅTABLE 2 Correlation coefficient determined for the set of authentic signals spoofi ng measurements were conducted inside a modern three story commercial building The spoofi ng signals were generated by a hardware simulator HWS and radiated for a few minutes indoors using a directional antenna pointing downward to affect only a small area of the building The intention was to generate NLOS propagation conditions with signifi cant multipath The second data collection scenario was based on measuring authentic GPS L1 C A signals under open sky conditions in which case the authentic GPS signals are temporally highly correlated At the particular instance of the spoofing and the authentic GPS signal measurement scenarios the SVs were distributed as shown in FIGURE 4 The GPS receiver in both scenarios consisted of an active patch right hand circular polarized RHCP antenna and a down conversion channelizer receiver that sampled the raw complex baseband signal The total data record was subsequently processed and consisted in acquiring the correlation peaks based on 20 millisecond coherent integration of the spoofing signals and in extracting the channel gains as a function of time FIGURE 5 shows a plot of the samples of the magnitude of despreader outputs for the various SV signals generated by the spoofing jammer and authentic signals The signal magnitudes in the spoofing Security RECEIVER DESIGN case are obviously highly correlated as expected since the jammer signals are all emanating from a common antenna Also the SNRs are moderately high such that the decorrelation due to the channel noise is not significant The pairwise correlation coefficient using Equation 4 are calculated for the measurement results represented in Figure 5 and tabulated in TABLE 1 and TABLE 2 for the spoofing and the authentic cases respectively As evident and expected the correlations for the spoofing case are all very high This is anticipated as the spoofing signals all occupy the same frequency band with exception of small incidental shifts due to SV Doppler Conclusions Spoofi ng signals generated from a common source can be effectively detected using a synthetic array antenna The key differentiating attribute exploited is that the spoofi ng signals emanating from a single source are spatially correlated while the authentic signals are not The method works regardless of the severity of multipath that the spoofi ng or authentic signals may be subjected to The receiver antenna trajectory can be random and does not have to be jointly estimated as part of the overall spoofi ng detection A patent is pending on this work Manufacturers The experimental set up used a Spirent GSS7700 simulator National Instruments receiver NI PXI 5600 down converter and NI PXI 5142 digitizer modules TECOM directional helical antennas as the transmitter antenna and NovAtel GPS 701 GG as the receiver antenna JOHN NIELSEN is an associate professor at the University of Calgary ALI BROUMANDAN is a senior research associate in the Position Location And Navigation PLAN group at the University of Calgary He obtained a Ph D in Geomatics Engineering from the University of Calgary in 2009 GERARD LACHAPELLE holds an iCORE CRC Chair in Wireless Location and heads the PLAN Group in the Department of Geomatics Engineering at the University of Calgary Dynamic Capture Geo Imaging Solution GPS Ready Camera Captures Location Data with Your Images Data Imaging Solution Barcode Ready Camera Relates Images to Barcodes All Of This In One Camera The Ricoh 500SE Ruggedized Waterproof Design Wireless Ready Bluetooth or WIFI Connects to Laser Range Finders Populate Data While in the Field Combines Images and Data Easily Embed Data in Image Header Store Sound in Image Header Streamlines Workflow Customizable Firmware Optional GPS Mounts to Camera Dynamic Storage New Cloud Content Management Index Store Manage Search Retrieve User Friendly Interface Versatile Scalable Disaster Protection Remote Collaboration Secure File Access 24 x 7 Trial Dynamic Storage Free for 90 Day Ricoh Dynamic Capture www RicohDC com 19098909039 www gpsworld com September 2010 GPS World 33