Good Timing

“Our main business is synchronizing and timing,” says Chronos founder and Managing Director Prof. Charles Curry. “Our clients include Vodafone, Telefónica O2, Three UK and EE, the ‘big ones’ in British telecom, as well as a number of other UK and non-UK wireless and wire line carriers. With this group, we can speak from a well-informed position in the telecom synchronizing and timing business, at least in Britain.”

Network synchronization, or “sync”, is essential to all modern telecom networks. Sync ensures that telecom services are continuously available and reliable. And the quality of timing and sync that goes into a telecom network, in turn, has real consequences for the quality of delivered voice, video, and data services. In fact, timing and sync quality have become a key differentiator in the highly competitive telecom carrier market.

“Timing today does use GPS at core locations, with some backup technologies,” Curry says, appending a caveat. “But GPS is vulnerable, and thus timing and sync are also vulnerable, especially to GPS jamming and other interference.”

In a recent report on GNSS vulnerabilities, Chronos says that while today’s Frequency Division Duplex (FDD) wireless telecom networks must meet a standard based on fractional frequency error—one part per billion—the incoming generation of 4G networks will use Time Division Duplex (TDD) techniques and a new performance metric, phase error, which requires sub-microsecond time accuracy.

New services and capabilities carried over these 4G networks, such as Coordinated Multipoint (CoMP) in which a handset communicates with a macro site and a small cell site simultaneously, will need a timing source with an accuracy of 500 nanoseconds, and this is at the edge of the network.

Some organizations are already providing this by using GPS alone, as is the case with Code Division Multiple Access (CDMA) networks. However, recent jamming attacks on South Korea by North Korea have demonstrated very clearly what can happen when GPS is compromised under this approach: numerous CDMA mobile phone sites lost their timing and failed.
A similar loss of cells was seen in the United States as far back as 2007 when a warship in San Diego harbor accidentally jammed GPS signals in the city, causing parts of the city’s cellular networks to shut down for up to three hours.


“As so much of our business depends on GPS, we wanted to know more about jamming, and we managed to find a generous source of funding in the form of the Innovate UK research program,” says Curry. “We called our project ‘SENTINEL.’”

The SENTINEL Project, which ran from 2011 to 2014, investigated a number of interconnected activities involving mission-critical or safety-critical services that need to be able to “trust” the accuracy and availability of GNSS signals at the point of use.

One simple but very important conclusion highlighted in the final project report was that the GPS jamming threat is getting worse.

“Under SENTINEL, we set up sensors in different parts of the country,” Curry explains, “to look for instances of jamming. One of the sites we chose was a certain UK-based telco rooftop in London, specifically the one above Keybridge House in Vauxhall. This is a high building, 15-stories tall, and important, what a major UK-based telco called an ‘international gateway,’ a key node in their network.”

Very quickly, researchers monitoring the sensor atop the building noticed a lot of interference. What was causing it? It’s still hard to say, says Curry.

“The cause could have been a line-of-sight, microwave radio link, just traversing that roof space. Most likely this would be coming from a tall building nearby, and there are plenty of those to choose from in London. It would actually most probably be a harmonic effect, a radio link with a harmonic that would sit on top of a GPS signal.” Beyond that, he says, there’s just no telling.

“In the meantime, we’d heard about a new anti-jamming antenna,” Curry says, “and we thought it might be interesting to give it a try, as long as we were up there and with a regular pattern of interference to test it against.”