GPS reversal event on April 6th could have side effects

On April 6, the Global Positioning System will arrive at the end of an era, or more accurately, of an era. It is at this point that the Coordinated Universal Time (UTC) clock used by the satellite navigation system will reach the limit of its 10-bit "week number" counter (WN) and will return to 0000000000 .

The GPS time is related to the official UTC time provided by the US Naval Observatory. But the GPS version of the clock follows the date counting the number of weeks since the beginning of the current GPS "epoch" – August 21, 1999. The clock reaching midnight tonight on the prime meridian, the GPS calendar become 20 years obsolete.

This should not be a surprise for most newer GPS navigation systems. There have been many warnings: the GPS has already undergone a similar reversal. And the Department of Homeland Security's National Cybersecurity and Communications Integration Center warned in April 2018 that this would happen, as it will happen every 1024 weeks, until that the modernization of the GPS constellation is completed, then the WN meter will be expanded. at 13 bits.

Most recent GPS receivers will ignore the switchover because they have been programmed to adapt to the change of the times. But old systems will not do it – and that can have interesting side effects, because the timing data skips 19.7 years. The clock change will not directly affect the location calculations. But if GPS receivers do not properly account for failover, time stamps in location data may corrupt navigation data in different ways.

But navigation is not the only concern. Many systems use time for other purposes – cellular networks, utilities, and other industrial systems use GPS receivers for synchronization and control functions. Since many of these systems have an extremely long life cycle, they are the ones most at risk of not being updated.

The problem of turnover is not limited to one day. Due to the way in which some manufacturers have accounted for the switchover date in the past (by hard coding a date correction in the receiver's firmware), their systems may fail at an arbitrary later date. Some have already succumbed: in July 2017, an old GPS system NovAtel broke down and, although the company has issued a notice several months earlier to warn users of the firmware upgrade, many would have ignored until that happens. Motorola OncoreUT + systems and some receivers using Trimble GPS engines have also failed in the past three years for similar reasons.

If you have a built-in GPS receiver for one of your existing assets in recent years, do yourself a favor today and check to see if a firmware update is up-to-date.