NovAtel's Annual Journal of GNSS Technology Solutions and Innovation

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Page 41 of 51

navwar velocity 2014 For more Solutions visit 42 With any GPS denied scenario, it is ideal to have situational awareness to know if jamming (inten- tional or otherwise) is occurring so that actions can be taken to reduce or eliminate the jamming. No- vAtel® has been conducting research in this area by taking samples of the GNSS Radio Frequency (RF) spectrum and time-tagging the samples with precise GNSS time stamps. This is done with standard NovAtel OEM628™ receiver hardware. Neil Gerein, NovAtel's Defense Product Manager stated, "By analyzing short "snapshot" samples, we can not only detect jammers, but also "fingerprint" the jammer by examining the signal characteris- tics. Taking this one step further we have demon- strated that if multiple receivers can 'see' the jam- mer simultaneously we can determine the location of the interference source." "GPS Denied"–Spoofing Spoofing makes a victim receiver 'think' that it is at a different location than it really is. This occurs when an adversary generates a false signal that supplants the real signal. The most robust way to protect against spoofing is for an authorized user to operate a receiver like NovAtel's OEM625S SAASM GPS receiver, to track the military encrypted Y-code sig- nal on GPS L1 and L2. Users without access to Y-code can still protect against spoofing by using a multi-constellation, multi-frequency receiver. Fortunately, techniques that protect against normal interference and jamming can also protect against this kind of attack. Spoofing of GNSS is complicated and requires sophisticated equipment to generate the spoof- ing signal and good knowledge of the victim re- ceiver's velocity. The complexity of this spoofing equipment increases greatly if the adversary tries to spoof all known GNSS constellations simulta- neously. A multi-GNSS, multi-frequency receiver is used as a cross check against possible spoofing sources. Also, the false signal has to supplant the real signal, so normal anti-jam systems like No- vAtel's GAJT have a role in preventing the loss-of- lock on to the real signal. Likewise, multi-sensor navigation like NovA- tel's SPAN GNSS+INS technology is an excellent method to protect against spoofing, particularly if the additional sensors for the PNT solution do not depend on GNSS. IMUs used in NovAtel's SPAN systems rely on accelerometers (motion sensors) and gyroscopes (rotation sensors). These sensors cannot be spoofed. Other lower fidelity RF posi- tioning and timing solutions like eLoran are very difficult to spoof or jam because they use high- power fixed transmitting stations. In the same vein, optical techniques and "Sig- nals of Opportunity" (RF signals that were never meant to be used for navigation) when coupled with other PNT sensors are shown to be effective although the quality of the solution is highly de- pendent on sensor quality. Research to date has shown that signals like AM radio can be effective for nav- igation and timing applica- tions; and optical techniques can help with relative naviga- tion and absolute PNT when compared to a geo-referenced image database. "GPS Denied"– Signal Blockage GNSS can be denied in dif- ficult environments due to a lack of a clear line of sight FIGURE 2: Downtown Calgary denial scenarios: reduced GPS vs reduced GPS + BeiDou.

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