AEROSPACE, MILITARY & DEFENCE
Building PNT resilience with Silicon Timing
By Steve Pratt, Sr. director, marketing - Aerospace & Defence, SiTime I
n the modern era, cyber-attacks and other electronic sabotage against critical services, networks and utilities are becoming more powerful as societies depend increasingly on connected systems and infrastructure. Among critical infrastructure targets, interfering with Global Navigation Satellite System (GNSS) signals is an increasingly common technique.
Positioning, Navigation, and Timing (PNT) information is critically important for a wide variety of civil and commercial activities including air and sea transport, road haulage and private motoring, as well as general logistics. The UK government estimates that a 24-hour PNT outage could cost the economy £1.4 billion.
Attempts to disrupt GNSS navigation within a targeted area generally involve either involves broadcasting overwhelmingly strong signals in the frequency range of the satellite signals, which prevents receivers begins with jamming, causing the receiver to presents a stronger, fake signal with false information to misdirect the receiver’s
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and open-source tools can generate these shift a vessel or aircraft’s reported position, manipulate timing systems, create false velocity vectors, or seamlessly take over a receiver without triggering alarms. This is an extremely dangerous threat that can silently mislead navigation and timing systems.
drift in the receiver’s internal timing source is a key factor contributing to divergence between the calculated and actual positions.
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Navigation systems can fall back to alternative modes if satellite signals become unavailable, which can occur due to obscuring in urban canyons or other uses the last known position, heading and speed to estimate new position and can be assisted with an inertial measurement unit (IMU) to enhance accuracy. Comprising multiple sensors including accelerometers, gyroscopes and magnetometers, the IMU
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can help the system maintain a position estimate for several minutes or even hours. Cars, robots and autonomous guided vehicles (AGVs) can use data from wheel encoders, steering angle sensors and are also employed to track motion relative to visual references. Also, constraining the estimated path to roads, lanes, or known routes can reduce drift.
Although these fallbacks can be effective against unintended or unavoidable signal loss, the holdover time for which the system can continue to maintain acceptable positional accuracy is usually quite short. In the event of unwanted signal interference, such as jamming, a much longer holdover duration may be needed. The key to this is timing.
Stable and accurate timing Timing is critical in satellite navigation as position is calculated based on time-of- receiver. The receiver solves for both time and its own location as unknowns in the positioning equations. Hence four satellites must be in view despite calculating position by trilateration. While satellites use extremely accurate and stable atomic clocks to timestamp the exact moment each signal
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