AEROSPACE, MILITARY & DEFENCE
is transmitted, receivers have tended to rely on quartz-based timing. Although cost- effective and relatively compact, quartz related drift under environmental stressors. They also drift over temperature and due to ageing. The receiver must frequently realign its own timing with that of the satellites, when available. During an outage, drift in the receiver’s internal timing source is a key factor contributing to divergence between the calculated and actual positions. The divergence can become large if the satellite signal is unavailable for a long period. Silicon MEMS resonators have about 1000 times less mass than quartz components, which dramatically reduces vibration sensitivity. SiTime’s Endura super temperature compensated oscillator (Super-TCXO), ENDR-TTT, has acceleration sensitivity of 0.004 ppb/g with ±50 ppb frequency stability over temperature and low aging enabled by the MEMS manufacturing process. In real-world PNT applications, where quartz-based solutions these properties enable approximately 20 times longer holdover.
In defense systems, local timing with ENDR-TTT remains accurate enough for synchronising critical systems like imaging, datalinks and control functions, even when exposed to harsh temperature and vibration. This can extend mission operations without satellite signals, even during GNSS jamming. Moreover, extremely accurate local timing using a source such as ENDR-TTT enables begin with jamming, causing the receiver to lose the connection with the satellite signal and a spoofed signal is broadcast to capture the receiver during the reacquisition phase. As the attack duration grows, the search space in time and frequency the also increases. The spoofer captures the receiver by being the strongest signal inside the search space. Precision timing can minimise the search window and prevent the spoofer from capturing the receiver.
Precision timing tested In a recent test, a receiver containing the SiTime ENDR-TTT Super-TCXO evaded capture throughout a four and a half minute attack by maintaining a narrow enough even though the spoofer had knowledge of the vehicle’s location. The ENDR-TTT frequency stability was better than 0.1 parts per billion (PPB), contributing less than ten meters to the total search window.
range uncertainty by almost 60 per cent. from capturing the receiver.
Figure 1. Comparison of true and calculated positions.
Figure 1 shows the real and calculated positions of the receiver, which was mounted on board a boat, during the attack. The solid portion of the curve was recorded during the system self-calibration phase, while the dashed portion represents the jamming attack. During jamming, the receiver continues calculating its position accurately despite having lost satellite- present when the jamming ends but is unable to capture the receiver due to the narrow search window. Figure 2 shows the total range uncertainty as a composite of timing uncertainty and position uncertainty due to IMU error. Compared to the typical quartz TCXO performance, the superior stability of the silicon oscillator almost eliminates the timing component, reducing the overall
Future spoof resistance Historically, GNSS receivers have obtained relatively simple signal easily replicated by spoofers. All GNSS systems also now operate and complex signals that require 20 times the bandwidth and transmission power or meaconing. A GNSS receiver containing the ultra-stable ENDR-TTT Super-TCXO can easily detect the spoofer’s reference oscillator error, thus providing a critical
Conclusion
Attacking GNSS signals is expected to become an increasingly common technique as a wide variety of modern services rely on these satellites for position, navigation and are attacks that compromise navigation in commercial, private and military defence scenarios. Precision Timing, leveraging the stability of silicon MEMS oscillators, can enhance the accuracy of fallback navigation techniques based on dead reckoning and sensor fusion. In addition, by minimising the signal-acquisition search window and enhancing the ability to identify replicated signals, Precision Timing can
Figure 2. Comparing the impact of quartz and MEMS TCXO stability on overall range uncertainty. APRIL 2026 | ELECTRONICS FOR ENGINEERS 23
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