GPS Week Number Rollover (WNRO)

Dear customers, 

In the past, you may have ordered one or more Trimble modules or system level products. With this, we want to bring to your attention an upcoming event that could affect the performance of your GPS devices.

On April 6, 2019 there will be a GPS rollover that could affect all GPS / Timing units in the world, regardless of manufacturer.

The Background
In addition to providing an accurate location information, the Global Positioning System provides accurate timing information to many critical systems – power grid, communications, financial markets, emergency services, and industrial control to name a few. It also includes the ability to transmit the proper date and time to a receiver by supplying the receiver with the current week and the current number of seconds into the week. This allows the receiver to translate the date and time into a more typical format – day, month, year, and time of day.

However, the field from the Satellite system that contains the week number is a 10-bit binary number. This limits the range of the week number to 0 – 1023, or 1024 total weeks.

GPS week zero started January 6, 1980. The 1024 weeks counter ran out and rolled over on August 21, 1999. The week counter then reset to zero, and it has been recounting ever since. The next time the counter will reach week 1023 and rollover to zero is on April 6, 2019.

April 6, 2019 is the 1024^th week and unless a GPS module or application has already accounted for this, the date may not report accurately. If the application does not use the date or if there are other sources for the date outside of the GPS module, you may not be affected.

Which GPS Units are affected?
Below is a partial list ofTrimble GPS modules with part numbers and names.   The units that have the potential to be affected by the April 6 WNRO Event have a star (*) beside it.  Not all products will have the same WNRO date.  Even if your product is not affected by the imminent WNRO Event, all products have a WNRO date.  Please use the below links to review the bulletin of your particular product for full information.

Note:  Position data (lat, lon), velocity and PPS will continue as normal and will not be effected. Only the week number will be affected.  The actual time should not be affected. The Week Number problem just affects the calculated date.  Therefore, the roll over event should only affect the UTC date.  The position output will not be effected.

How to Fix?
Please review the bulletin for the particular module that you use.  For some devices, there is a fw upgrade that will allow your device to continue normal operation beyond the WNRO date.  Most Condor family devices have fw updates available to download. Unfortunately, some modules will not have a fw update available.

In lieu of a fw update to the GPS device itself, the customer may wish to update their fw on their end product to accommodate for the week number change from the GPS module.  Additionally if the end product is connected over the air to a backend....the fw on the backend application can be modified to accommodate for the week number change.

Should you wish to change your host fw on your device or backend to detect and correct the date......sample source code and instructions can be found here.