The GPS Week Number Rollover: what you need to know

Does your company rely on GPS to do business? Then you should make sure you’re ready for the GPS Week Number Roll Over.

Also known as the GPS Leap or WNRO, this event will affect many GPS receivers all over the world in April of this year. If your company is impacted, it could cause serious confusion and potential problems for your team and customers.

So, what’s this all about? How can you check if you’re GPS receivers are likely to be affected? And what can you do to prepare?

Let’s answer the big questions.

What is it?

Do you remember the Millennium Bug? As the year 2000 approached, organisations all over the world were checking and upgrading their computer systems to counteract the effects of a computer programming problem several decades in the making. As many programmes had been setup to recognise the year based on its last two digits, careful measures needed to be taken to ensure the turning of the calendar from 1999 to 2000 did not cause chaos.

The GPS Week Number Roll Over is similar. The week number is tracked as a 10-bit field in a GPS’ time message. For this reason, every 1024 weeks (referred to as an ‘epoch’) the week number must be reset. Everything goes back to zero and the count begins again.

What might happen?

If a GPS receiver is confused by the rollover, it’s possible that errors will occur. For example, a tracking device used as part of your fleet management processes may begin to operate based on information that is timestamped two decades ago.

When is it happening?

April 6th, 2019 is the official date of the GPS Week Number Rollover as that is when the current epoch comes to an end. However, even if you don’t experience system errors or confusion straight away, it’s possible that your GPS receivers will malfunction later on down the line.

This is because some receivers use firmware that ensures the reset comes 19 and a half years after the time of the device’s manufacture rather than after the last reset.

Hasn’t this happened before?

Yes, it has. The first GPS rollover occurred on 26 August 1999, 1024 weeks after the first GPS satellite was launched in 1980.

Is anything being done to stop this happening?

Absolutely. All aspects of the GPS’s performance are constantly being improved and this includes the way it manages the week number. Increasingly, there is a move towards using a 13-bit instead of a 10-bit data field to track week numbers, which will extend the length of the epoch from around 20 years to 157 years.

What should Webfleet Solutions’ customers do?

The good news is that the vast majority of  Webfleet Solutions products will not be affected by this issue. It is more than likely that your system will continue as normal from April onwards. However, as an error is still possible in some cases, we strongly advise all of our customers to check the status of their devices here.

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