Inside GNSS Media & Research

MAY-JUN 2018

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Page 46 of 67 M A Y / J U N E 2 0 1 8 Inside GNSS 47 remote adversary, including inertial, odometer barometer sen- sors; some are based on spatial-signal processing techniques, including multi-element or synthetic-aperture antennas; some are based on signal fidelity tests, which assess whether certain characteristics of the received signal fulfill the expectation of the receiver, being power levels, data content, modulation, or the presence of certain signals. e trust we can place in the receiver is therefore inherently tied to our estimate of the capabilities of the adversary, and how each of these relative capabilities might evolve over time. Unfortunately, advances in technology play in the favor of the ever-adapting adversary, not the user with installed equipment or infrastructure. ere is a risk that if the capability of the adversary is underestimated, or the difficulty of signal genera- tion is overestimated, then the user will be exposed. An addi- tional challenge is that it can be difficult to envisage how the adversary might approach the problem. As engineers, we are oen biased, even subconsciously, by best practices, rules-of- thumb, precedence, or general convention — we tend to use things in the way they are supposed to be used. In contrast, an adversary who is already committed to breaking the law is unlikely to hesitate to break some design rules too. In this article, we examine this problem through an exam- ple of multi-frequency signal generation via existing off-the- shelf low-cost equipment which was dismissed as incapable of such signal generation. It has been generally held that the generation of multi-frequency GNSS signals is beyond the capability of an "entry-level" adversary, and so multi-frequen- cy receivers are, to some extent, invulnerable. is belief is FIGURE 1 Example of the reported carrier-to-noise ratio for the re- ceiver under test, when broadcasting L1 C/A (green), L1 P(Y) (blue), L2 P(Y) (red), and L2C (yellow) from a narrow-band single-frequency transmitter centered between L1 and L2. The new AsteRx-i Best-in-class IMU enhanced GNSS PRECISE, RELIABLE WITH ATTITUDE septentrio . com/asterx-i

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