Will Your GPS Work After April 6?

Image: AFSPC

Image: AFSPC

Technology often lasts longer than it’s designers imagined, generally long enough that at least one design decision made in an early stage eventually rises up and threatens the ecosystem. The GPS system is about to encounter such an event - the counter rollover of 2019!

Yes, very much like Y2K, another counter issue. In this case a counter that stores how many weeks since the constellation of GPS satellites became active will be the problem. The design decision was made to use a 10-bit number to hold this information. A 10-bit number can store values from 0-1023. This rollover of the counter back to zero works out to April 6, 2019. This is sort of like the odometer in a car rolling over, except the implications are a GPS unit that produces incorrect location and/or time information.

I hear you saying, “but GPS has been around for more than 20 years.” You’re not wrong - the counter rollover has been encountered once before on August 21, 1999. Does that mean it is a solved problem? Hardly. Most modern units in the last 10-15 years are probably fine and many more have used firmware updates to clear up the issue. Manufacturers say the only units likely to be affected are older units that have not received firmware updates. I can think of a few disciplines that hang onto equipment for long durations of time with no internet connection and little want to update firmware; namely the earth sciences.

Many of our instruments sit in the field for decades churning out data, but its time to give a little checkup to your hardware friends and make sure they are prepared for this rollover. It never hurts to apply updates and check with your manufacturer for any service bulletins. You can also put the devices in a GPS simulator to simulate the transition. If your device is subject to the issue it could suddenly be time stamping your data incorrectly, making an already difficult problem of timed data acquisition even more of a nightmare.

So will we be worrying again in the next 19.6 years? It’s unlikely. Recent efforts to update and modernize the GPS system have a 13-bit counter in the plan. That works out to be about 157 years, a point by which we will likely have a much different system that the GPS of today.