Are multi-band GNSS receivers the key to 5G timing?

Ulrich Kohn
Satelites boucing information back to Earth

Satellite-based network timing underpins the world’s critical infrastructure. Coordinated Universal Time (UTC) sourced from GNSS keeps power utilities, transportation, global financial trading, cutting edge scientific research, and countless other sectors in sync.

Distribution of highly accurate UTC timing is also key to implementing 5G networks, particularly for time-sensitive URLLC applications including smart grids, autonomous vehicles and tactile internet for use cases such as telesurgery. This requires mobile network operators to carefully analyze the quality of their existing synchronization network and define a route towards nanosecond accuracy at their base stations. 

New specs for new times

So in today’s networks, timing is everything, and that means synchronization errors – even a difference of tens of nanoseconds – can be costly for operators and end users. New ITU regulations for primary reference time clocks (PRTCs) stipulate timing inaccuracies must be kept within 40 nanoseconds. This new PRTC-B specification also means operators have to deploy technology capable of compensating for errors such as delay variations of GNSS signals in real-time.

GNSS challenges 

Space-based signals are vulnerable in several ways. Activity on the sun and the planet’s day/night cycle can disturb the Earth’s ionosphere resulting in GNSS inaccuracy with timing errors at the receiver end. This is known as ionospheric delay variation (IDV).

GNSS is also vulnerable to malicious attacks like jamming and spoofing. The former blocks timing and location signals entirely, while the latter transmits false signals to the receiver with the potential to cause havoc in sectors such as aviation and medical care. 

So to circumvent GNSS’s inherent weaknesses, it helps to have a receiver capable of filtering out timing errors. As single-band receivers cannot compensate for IDV, they alone are not accurate enough for today’s requirements.

Rubidium-based clocks can filter out disturbances and offer redundancy when GNSS is compromised. A high-quality clock is an efficient way to keep accurate time. But rubidium devices are impractical because deploying them on a large scale is expensive. What’s more, they are less resilient to local environmental conditions.

Multi-band benefits

This is why our Oscilloquartz multi-band technology offers such a vital protection. It receives GNSS signals in several frequency bands and uses the delay differences between them to calculate and compensate for delay variation. This method is far more cost-effective than other techniques, such as deploying GNSS receivers with a filter implemented by a costly high-stability rubidium oscillator. 

Multi-band receivers are cheaper, scalable, and can be paired with timing solutions containing high-quality oscillators. Designed to meet PRTC-B and ePRTC standards, our Oscilloquartz multi-band, multi-constellation receiver exists as a pluggable line card. 

How it works

The device measures propagation delay difference across the upper and lower L-band then calculates the difference between signals. That information is then used to eliminate inaccuracies caused by IDV. 

With our multi-band receiver’s advanced detection mechanisms, you also get improved resilience to jamming and spoofing. And because the device is multi-constellation it can access a higher number of satellites, delivering enhanced redundancy in the event a signal is compromised. 

Multi-band is extremely precise, so you don’t need to rely on grandmasters with expensive rubidium oscillators. But let’s say you’re supporting an application that needs even higher levels of redundancy and accuracy, what then?

Flexible, robust, accurate

Our Oscilloquartz GNSS multi-band line card plugs into both our OSA 5430 and 5440 core grandmasters, both of which support PTP, NTP and SyncE over multiple 1Gbit/s and 10Gbit/s Ethernet interfaces. The solution not only satisfies the ITU’s stringent PRTC-B specs, it now gives the most accurate UTC-based timing information available as part of an enhanced primary reference time clock (ePRTC) solution. 

The pairing of a high-quality quartz, rubidium or cesium clock with a multi-band GNSS receiver delivers nanosecond precision coupled with phenomenal holdover capability. Depending on the application, this may be the setup of choice. In combination with our recently launched optical cesium clock, the accuracy of multi-band GNSS receivers is complemented by unprecedented holdover characteristics for the most stringent timing requirements in our industry.

Operators want to future-proof timing networks, and naturally, they want to do so in the most cost-effective way possible. The evidence is clear – multi-band GNSS receivers are one of the most effective and cost-efficient ways to go.

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