![]() If the users of these receivers had been aware of the problem, in many cases they could have obtained a firmware update from the manufacturer before the receiver failed. But because they were manufactured near the end of that epoch, the manufacturers were able to implement pivot dates in 2014, 20 – causing problems nearly 20 years after the epoch ended. These receivers were still running their original firmware from the first GPS epoch, which ended in 1999. In November 2017, the US Naval Observatory published a partial list of legacy receivers that started to malfunction on dates in December 2014, February 2016, August 2016 and July 2017 – see slide 22 of this PDF presentation. We already have some good insight into how hard-coded pivot dates can create problems long after the official epoch rollover day. Week Number Rollover issues have happened before To improve the situation regarding Week Number Roll Over, message types (CNAV and MNAV) use a 13-bit field to represent the GPS week number and newer GPS receivers that utilize that 13-bit field will not have a problem with 1,024-week epochs. The upgraded features include new civilian and military GPS signals. The GPS modernization program is an ongoing, multibillion-dollar effort to upgrade the features and overall performance of the Global Positioning System. This diagram shows how hard-coded pivot dates work: In effect this means that older GPS receivers will operate normally for almost 20 years before problems begin to occur – and if firmware is implemented in this manner, no issue is likely to be seen when the GPS epoch changes.įor example, while the second GPS epoch began on 26 August 1999, a receiver manufactured in January 2005 may have a “pivot date” of January 2005 + 1,024 weeks coded into its firmware – meaning it will function smoothly until August 2025. That’s because many receiver manufacturers have sought to maximize the default lifespan of their receivers by implementing the 1,024-week limit from the date the firmware was compiled, rather than from the date the current GPS epoch began. In fact, it’s much more likely that an affected receiver won’t start outputting erroneous data until long after the 6 April 2019. One of the things that makes this issue different from the Millennium Bug is that the impact won’t necessarily be felt on rollover day itself. Problems could occur on or after 6 April 2019 That means from that date onwards, we are likely to start seeing rollover problems in GPS receivers that aren’t programmed to cope with the week number reset. We are now nearing the end of the second epoch, which will fall on the 6 April 2019. The first GPS satellites went live on 6 January 1980, meaning that the first epoch of GPS time lasted until 21 August 1999. Each of these periods is known in GPS terms as an “epoch”.Īt the end of each epoch of 1,024 weeks, the receiver resets the week number to zero and starts counting again. GPS used a 10 bit field to encode the week number in each GPS time message, which means that a maximum of 1,024 weeks (19.7 years), could be handled. The Week Rollover Problem is a known issue caused by the way that GPS used to handle the week element of the data that forms an essential part of the navigation signal. The good news is, it’s easy to check now whether your receivers are affected or not, giving plenty of time to implement a solution.īut first, let’s look at what’s causing the problem. Similar – but different – to the Millennium BugĪs we’ll see, it’s not quite the Millennium Bug for GPS receivers, but it does share some similarities. (To give just one example, GPS trackers employed in a fleet management system to track deliveries could cause system errors or even a crash if they suddenly start to output location data timestamped with a date 20 years in the past.) But it will create week, month and year timestamps that are wildly wrong, which could seriously impact any systems and applications that rely on GPS data at that level. This won’t affect the receiver’s ability to navigate and/or calculate precise time from the day level down to the microsecond level. The data they output may suddenly jump backwards in time, putting timestamps on your timing and navigation data that are nearly 20 years out of date. If they are, you may find your receivers start to behave strangely on – or more likely at some point after – 6 April 2019. If your vehicles or equipment rely on GPS receivers, now is the time to check if they’re affected by the GPS Week Number Rollover issue. Here’s what that means and how to check if a receiver is vulnerable. Tags: GPS Interference, Week Number Rollover Problem Some GPS receivers may malfunction on or after 6 April 2019 due to the GPS Week Rollover. Blog The GPS Week Number Rollover problem
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