Testing a GNSS receiver’s response to RF interference used to be a pretty major undertaking.
One of my first ever projects in the GPS world was to test anti-jam antenna systems to evaluate how they coped with signal jamming.
In those days it was difficult to create wholly realistic scenarios with injected RF interference in the lab. So, to conduct the test, we set up scaled-down jammers on an open test range located in the South East of the UK. One of my abiding memories is of having to be vigilant over calibrating and adjusting the signal level of the jammers so that the interference we caused wouldn’t spill out beyond the range and interfere with nearby equipment.
The unintentional effects of open-air jamming tests
Collateral damage is something of an occupational hazard when it comes to large-scale, open-air interference tests. In 2007, a US Navy jamming exercise near San Diego knocked out cellular networks in the city, which were unable to synchronise time while GPS signals in the area were being jammed. And in April 2015, a US Air Force interference test in Idaho caused significant disruption to GPS-reliant agricultural businesses operating nearby.
But, while they can be disruptive, those kinds of tests are utterly necessary - and not just for military users of the GPS system. Today, it’s also critically important for commercial manufacturers to understand how their location-aware systems perform in the presence of RF interference.
GNSS interference is becoming more common
That importance is growing for two reasons. Firstly, interference to GPS and other global navigation satellite systems (GNSS) is becoming more common, mainly due to more people buying illegal jammers for personal use. At a conference I attended in June, over 70% of the attending equipment manufacturers, professional users, designers, and system integrators agreed that GNSS interference is getting worse.
And secondly, humankind’s reliance on GPS and GNSS is growing fast. It’s an essential element in connected and autonomous vehicles. It drives precision agriculture, construction and mining. It sits at the core of consumer products like exercise trackers and games like Pokémon GO (whose runaway success is sure to usher in a whole wave of location-based augmented-reality games).
And that’s only on the geolocation side. GPS and GNSS also play a critical role in precision timing for everything from mobile networks to power grids and financial trading systems. In 2011, the US Department of Homeland Security said that 15 of the country’s 19 “Critical Infrastructure and Key Resources” sectors relied to some degree on GPS-based timing.
So understanding the resilience of a GPS-based system to interference is essential. But can it be done without setting up very expensive - and potentially widely disruptive - open-air jamming tests?
A more effective approach to interference testing
That’s one of the questions I’m going to address in my conference session next Friday afternoon at the ION GNSS 2016 conference in Portland, Oregon
Together with my colleagues from Spirent’s Professional Services team, we’ll present the results from a lab-based test framework and methodology we’ve developed for measuring and comparing receiver performance in the presence of GPS signal jamming.
The testbed can combine GNSS signal simulation with lab-based playback of real, recorded jamming incidents for maximum verisimilitude, and is designed to make interference testing rapid, repeatable and highly automated.
To illustrate the need for such a test, we’ll show the (anonymised) results we obtained from testing three widely-used, commercial-grade receivers in the same jamming scenario.
If your role includes selecting GNSS receivers for integration into a wider system, you should find our initial results quite interesting, and I’d definitely recommend you attend the session. And if you’re interested in talking more about measuring receiver robustness, do come and speak to us on the Spirent stand - see the details below.
ION GNSS 2016: Spirent session and stand details
Developing a Real-World Test Framework and Methodology for PNT Systems and Devices will be presented by Guy Buesnel, John Pottle, Fabio Simon Gabaldon and Mark Holbrow in Conference session e6B (Interference and Spectrum Protection 2) from 1345-1655 on Friday 16th September at ION GNSS 2016.
Visit Spirent at Stand A in the Exhibit Hall on Wednesday 14th and Thursday 15th September.