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Developers of high-end GNSS timing receivers face new test challenges

trainFrom telecommunications networks to energy grids and financial services, much of our critical infrastructure relies on the precise time signal broadcast by global navigation satellite systems (GNSS) like GPS, GLONASS, Galileo and BeiDou.

According to the US Department of Homeland Security, these are sectors whose “assets, systems, and networks… are considered so vital […] that their incapacitation or destruction would have a debilitating effect” on the country.

The receivers used by these industries to obtain precise time must be robust, resilient and capable of performing to expectation. As the GNSS environment – and the threats to it – continues to evolve, receiver developers must evolve their test approaches to keep pace.

The three GNSS threat classes

The signals broadcast by global navigation satellite systems (GNSS) are the first source of timing information used by critical infrastructure operators to synchronise and timestamp activity across their networks.

Because it comes from the atomic clocks on board each navigation satellite, GNSS time is ideal for applications that require accurate and precise measurements within a tolerance of hundreds of nanoseconds. But as GNSS signals come from Medium Earth Orbit satellites in space, their power level is below noise floor. Because the signals can be faint, even minimal disruption can affect signals and prevent the synchronisation required by critical infrastructure.

In fact a 2018 DHS report identifies three threat classes that can put the signal – and the infrastructure that relies on it – at risk:

  • Interference, jamming, and atmospheric disturbances that can degrade a receiver’s ability to process signals and prevent it from obtaining a PNT fix
  • Spoofing signals that mimics GNSS signals to cause a target receiver to produce incorrect measurements
  • Hacking software that introduces incorrect digital data to a receiver, altering how it calculates positioning, navigation and timing

The risks to critical infrastructure

Some of these threats are established and well understood. However, disruption methods like jammers are becoming more widespread and more accessible, and pose a growing risk to critical infrastructure.

Modern cellular networks, for example, rely on continuous time synchronisation across the network to transmit data effectively. In 5G networks, if base stations are out of sync, network capacity and throughput can be degraded – harming quality of service.

In the energy sector, an electricity grid will use a primary reference clock to obtain precise time, which is then synchronized to all clocks on the network. And in financial trading networks, institutions often use GNSS-derived time to timestamp transactions down to the sub-second level.

In each of these applications, a disrupted or compromised GNSS time signal can lead to errors with potentially serious ramifications – like loss of cellular data service, power outages, or cancelled transactions.

We got an idea of the potential disruption in 2016, when a glitch in the GPS system caused several GPS satellites to broadcast time that was 13 microseconds out. Digital radio and television broadcasts, telecoms networks and computer networks all reported issues over a 12-hour period.

Developers seek to make timing receivers more robust

With so many factors affecting performance, timing receiver developers for the critical infrastructure market are continually exploring new ways to make receivers more reliable, robust and resilient – and that presents new test challenges.

Those measures may include supporting multiple GNSS constellations and frequencies, incorporating advanced anti-jam and anti-spoofing technologies, and – for European operators – potentially gaining authorisation to use the secure, encrypted Galileo PRS signal rather than rely on the open one.

Thorough testing is essential

As performance and security measures evolve, so will the test regimes that ensure they perform to expectation. Timing receiver developers serving the critical infrastructure market will need to thoroughly test how their receiver design:

  • Receives and processes time signals from more and more GNSS constellations and frequencies – both open and encrypted
  • Handles signal obstructions such as multipath and obscuration
  • Responds to man-made interference from jamming devices, adjacent band activity and noise from nearby circuitry
  • Reacts to spoofing attempts – and if it can even detect when these attacks are happening
  • Copes with natural interference like ionospheric effects and solar flares

Prepare for the future with Spirent

Spirent is committed to helping developers characterise GNSS timing receiver performance – today and into the future.

Our multi-frequency, multi-constellation GNSS simulators offer the flexibility to test receivers with all current GNSS signals and frequencies, including regional augmentation systems and classified signals. We’re also committed to implementing new signals and ICDs as they’re introduced, so you can start testing with new signals straightaway.

With our GSS7725 Interference Generator you can evaluate how a receiver performs in the presence of interference sources like jamming.

Providing a low RF to 1PPS delay, the GSS9000 is equipped to test receivers against even the most stringent timing criteria. We offer extensive test scenarios and professional advice to help you assess conformance to standards like ITU G.8272 for Primary Reference Time Clocks in cellular networks, and will add to these as future standards emerge.

Questions about current or future Spirent capabilities? Get in touch

If you’d like to know more about future-proofing your timing receiver testing with Spirent, or if you have any other questions, please do get in touch.

 
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