What you need to know about the GPS Week Number Rollover


Does your company rely on GPS or use equipment that relies on GPS to function? If so, it’s imperative you ensure your business is ready for the GPS Week Number Roll Over (WNRO).

Also known as the GPS Leap, this event will affect many GPS receivers in Australia and will take effect from 6 April 2019. If your company is impacted, it could cause serious confusion and potential problems for your team and customers.

To help prepare your business, leading telematics solution provider, TomTom has answered some of the more important questions you may be asking in the wake of WNRO.

What is GPS Week Number Rollover?

Do you remember the Millennium Bug? As the year 2000 approached, organisations all over the world were upgrading their computer systems to counteract the effects of a programing issue several decades in the making. As many programmes had been set up 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 WNRO is similar. All GPS receivers use a 10-bit field to encode a GPS’ time message. In other words, there is a limited amount of possibilities to be shown on the clock. This allows up to 1,024 weeks to be handled and is referred to as an ‘epoch’.

For this reason, every 1,024 weeks, the system clock must be reset. Everything goes back to zero and the count begins again. However, when the calendar resets, it causes a miscommunication between GPS satellites and GPS receiver chips. As a result, some chips in driver terminals will lose the ability to process certain functions.

What does this mean for my business?

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 process, may begin to operate based on information that is timestamped two decades ago. To avoid any potential errors in your fleet, we recommend checking the status of your GPS equipment before the WNRO takes place.

When is the number rollover happening?

6 April 2019 is when the current epoch comes to an end and the GPS WNRO begins. However, even if you don’t experience system errors or confusion straight away, it’s possible that your GPS receivers will malfunction later down the line. This is because some receivers use firmware that ensures the reset comes after the time of the device’s manufacturer date, rather than after the last reset.

Has this happened before?

Yes, it has. The first GPS rollover occurred on 26 August 1999, 1,024 weeks after the first GPS satellite was launched in 1980.

For the most part – everything continued on as normal with little implications. However, that does not mean you should ignore this WNRO. Simply ensuring your software is up to date can mitigate future technical glitches.

Is anything being done to prevent this from happening again?

All aspects of GPS performance are constantly being monitored and 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. This would extend the length of the epoch to around 157 years versus the current standard of approximately 20 years.

What should businesses do?

It’s important to check in with your GPS software provider. They can help share the status of your device and/or equipment to help your business better prepare for the WNRO.  


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