GPS Week Number Rollover part two coming for old devices next month

JC Torres - Oct 21, 2019, 5:36 am CST
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GPS Week Number Rollover part two coming for old devices next month

GPS, short for Global Positioning System, is almost universally known as the technology that helps tell our location in the world. What few probably know is the system is actually designed to also tell the time. GPS receivers have actually relied on this piece of data coming from satellites not only to tell time but to actually make location-based services work properly. Unfortunately, that system might be thrown into chaos for the second time this year when a second GPS Week Number Rollover hits old devices in early November.

Humans may have an almost innate understanding of time but computers don’t. They simply record the passing of time in a string of numbers, leaving it to software to interpret and convert to something humans can read. That number format is often limited by convention or by the technology used at the time period. The Y2K “bug”, for example, was caused by some systems using only two numbers to represent the year. The averted Unix time rollover, on the other hand, would have been caused by a 32-bit limit on the number of seconds used to represent “epoch time”.

The GPS Week Number Rollover situation is similar to the latter. Due to hardware constraints, the system counted weeks in a space that only had room for 10 bits which, in decimal, meant it could only count from week 0 to week 1,023. Once it hits week 1,024, the week number counter goes back (rolls over) to 0, which could cause GPS receivers to function incorrectly.

Fortunately, this “GPS Week Number Rollover” only happens every 19.7 years, the first one being August 21, 1999 and the second just last April 6, 2019. Even better the GPS was updated to use 13 bits so that the rollover only happens every 157 years instead. Unfortunately, the rollover earlier this year, which went by without much incident, might have missed some devices. Apple is now warning owners of iPhones and iPads launched in 2012 and earlier that they will be affected by this next rollover which takes place November 3, 2019 at 12:00 AM UTC.

Apple’s solution is simple: just update your device to iOS 10.3.4 or, barring that, iOS 9.3.6. Verizon is giving the same warning but is strangely lumping in other older Android devices from Samsung, Google, and others. Unsurprisingly, it is also taking the opportunity to encourage owners of these devices to upgrade to a new one from the carrier, provided they’re eligible, of course.


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