Mobile security

We're Jamming: GPS Weakness Could Sink Wireless

A timing expert from the National Institute of Standards is concerned that the ease with which GPS signals can be jammed could spell trouble for wireless networks, as well as many other commercial endeavors, in the coming years.

Dr. Marc Weiss of the Time and Frequency division of the US National Institute of Standards and Technology (NIST) laid out his concerns at the recent Mobile Network Security Strategies conference in New York City. Weiss said that wireless networks increasingly require pinpoint accurate timing to synchronize transmissions between basestations and deliver faster connectivity, and they rely on global positioning system (GPS) signals from satellites to deliver that data.

"Most industries don't even know how dependent they are on GPS," Weiss told the crowd. "The problem is it's vulnerable -- the signals are extremely weak."

Weiss should know -- he's been working in this field for more than 30 years. (If you want to dig into the technical details of using a GPS signal to synchronize clocks to a standardized time, here's a paper he wrote on the topic in 1980.)

Weiss said it only takes a picowatt at the antenna to block GPS signals in the vicinity. "I've heard of garage door openers blocking GPS," he said.

This means that a number of unintentional and malicious jamming possibilities could drown out GPS and thereby affect transmissions over wireless networks.

Weiss cited the infamous example of a trucker who sped past Newark airport at the same time every week with a GPS jammer blazing -- to stop being tracked by his employers -- and shut down the navigation systems at the airfield.

And regular Light Reading readers will remember the major problems that LightSquared faced because its network signals were found to interfere with GPS. (See LightSquared: The Company That Won't Die.)

The issue is set to become an even greater concern as small cell basestations are added to the edge of mobile networks, and it was a topic of debate during the Q&A session at the end of Weiss's presentation. Several conference attendees asked whether the Precision Time Protocol (PTP) could be an alternative method of synchronizing radio access network infrastructure. (See Synching Up Small-Cell Backhaul.)

"The problem with PTP is you can only go a couple of hops and have it keep the timing," said Weiss. (It should be noted that some in the audience didn't appear to agree with that analysis.)

Weiss's real concern, however, is the prospect of malicious jamming from parties deploying much more powerful megawatt devices. North Korea has reportedly been attempting to use such transmitters to block the GPS on US spy planes since 2011.

The NIST guy's worry is that someone could smuggle a powerful jammer into a big city such as New York and blot out navigation channels and communications networks while remaining undetected. "The US lacks the capability to rapidly detect and geo-locate malicious GPS jamming."

As Weiss suggests, this has wider implications beyond the wireless industry. He also said that GPS spoofing has already been used to take down a "drone helicoper" by convincing it that down was up. (See Here Come the WiFi Drones.)

— Dan Jones, Mobile Editor, Light Reading

year2525 12/16/2013 | 2:40:03 PM
Re: Need for fallback So is it, to your knowledge, being implemented in small cells yet?

Weiss seemed to believe that European carriers were spending more on alternatives to GPS than their US counterparts.
Vitesse Semiconductor 12/16/2013 | 2:37:14 PM
Re: Need for fallback It is already commercially available
year2525 12/16/2013 | 1:22:50 PM
Re: Need for fallback So would you say this silicon is widely commercially available yet? Or testing, sampling etc?
Vitesse Semiconductor 12/16/2013 | 1:16:16 PM
Re: Need for fallback We agree, in part, with Dr. Weiss' assertion that PTP can only maintain timing over a couple of hops. However, this is an implementation issue, rather than a protocol-specific issue. If network operators implement a simple, low-cost transparent clock or boundary clock on intermediate nodes, they can maintain PTP timing over many, many hops. An ITU-T demonstration in 2012 showed that time stamping in the PHY chips can keep time errors around 25-50ns – even over 10 hops. For transparent clocks, these time errors can be filtered out so they typically will perform even better.  This level of accuracy is sufficient even for LTE-Advanced, which requires times errors of 500ns or less. For macro networks, therefore, PTP can be a perfect backup to GPS. Plus, operators can move grand master clocks further into the network to be housed in secure locations where GPS is harder to compromise.

For small cell networks though, GPS becomes far less reliable. Thanks to recent advances in silicon technology, PTP can maintain timing without interfering with network encryption. Any multi-hop network requires this combination of security and timing, but small cells are particularly vulnerable and will need to rely on PTP as the primary timing solution.

Sarah Reedy's article from late November, and the discussion that followed, highlighted small cells' dual challenge of security and timing:

DanJones 12/11/2013 | 11:34:34 AM
Re: Need for fallback Yep, add more LTE cells in the form of small cells and the sync and phase problem gets worse too.
rameshchandra0 12/11/2013 | 1:22:46 AM
Re: Need for fallback This is more prone to LTE because of phase requirement. I guess, development of boundary clock functionality in transport shall maintain phase & frequency to more number of hops in PTP. Having PTP does not rule out jamming of GPS used with Grandmaster impacting whole network.

There is need for develoment of periodic reactivation of GPS while Grandmaser is in holdover mode for couple of hours. 

DanJones 12/10/2013 | 11:08:07 AM
Re: Need for fallback Yes, Weiss suggested that European carriers are actually spending more on hardware assisted PTP, which he said works as a back-up/supplement to GPS.

He doesn't think US carriers are investing in assisted PTP so much because they haven't seen problems with GPS yet and so don't see the need to spend the money on it.
MordyK 12/10/2013 | 10:41:00 AM
Need for fallback This highlights the need for backups to the "newfangled" technologies.

The early cellphone and car navigation systems relied solely on GPS which caused problems in urban canyons and under overpasses, but adding in WiFi and Cell ID along with sensor fusion which brought the old dead reckoning into the mix improved it.

The same applies to all new technologies, where its important not to forget the old which can be used as a fallback as well as creating backups - even at considerable expense - to ensure that services we come to rely on simply don't collapse.

During the blackout a few years back this came to the fore when old plain phones had DC power and service but most peopledidnt have operating phones because the were using "smarter"phones - or VoIP - which required AC power, which was also why the internet went down.

This same issue arose with Sandy when cell towers relied on a single source of both power and backhaul, which when cut effectively disabled the network (even with a few hours of diesel). There are technologies such as microwave and some new power sources which while expensive can be used for alternative sources, which although not cost effective nor "entirely" capable of supoporting our new needs, can still provide interim reduced capabilities.
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