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GPS to have it's 2ⁿᵈ Y2K Moment on April 6 This Year
Posted by alexkemp on 12 February 2019 in English. Last updated on 13 February 2019.Is Location on my Smartphone going to die? OS updates may well be available, but Vodaphone stopped providing them 0 secs after I bought it.
(boring detail from the Register link above follows)
GPS satellites contain an atomic clock, and the signal that they put out contains a timestamp derived from that clock. The timestamp is an inherent part of the way in which a device Location is calculated from the accumulated GPS signals. However, that Timestamp stores the week number using ten binary bits…
Ten binary bits == 2¹⁰ == 1,024 weeks ≈ 20 years
The first GPS satellite launch was 1978. The first epoch was 6 January 1980 & the first rollover was midnight UTC Sun 22 Aug 1999 & the next will be the first Saturday in April 2019. Yikes!
Extra
If you want to see the timestamp for a JPEG with embedded Location info, then do this (and note: this was done because the time went weird for this set of photos (all 3 timestamps should be the same)):–
$ identify -verbose 2016-10-08_11-27-27.jpg | fgrep 'exif:DateTime'
exif:DateTime: 2016:10:08 10:27:27
exif:DateTimeDigitized: 2016:10:08 10:27:27
exif:DateTimeOriginal: 2016:10:08 21:58:52
Phew! We are all Saved!
I’m indebted to TheSwavu (see Comments) for a link to wired.com detailing how everything went fine (?) on the last time this happened in 1999:–
At 8 p.m. EDT Saturday (21 Aug 1999), the clock was reset to zero
The US Coast Guard said it was unaware of any serious distress calls from boaters related to malfunctioning GPS receivers.
He said fewer than 12 Coast Guard cutters, aircraft, boats, cars, and other auxiliary vessels reported a glitch, however fleeting, when their GPS receivers failed to update automatically. Fixing those short-lived glitches typically required nothing more than powering down a GPS receiver to get re-synchronized with the satellites, McPherson said.
In Japan, Pioneer Electronic, one of several car navigation system makers, said it had received several hundred phone calls Sunday from customers whose devices failed because they baulked at the clock resetting. Some of the older models, made before 1995, were now showing the date of 7 January, 1980, as if this were Day 2 back in the original week 0. But they were otherwise showing the correct position and time, he said.
So there we are. Only 12 US Coast-Guard vessels & several hundred Japanese customers. So it is all going to be OK. As long as you do not work for the Coast Guard. Or are Japanese (or, god forbid, are a Japanese Coast Guard). And if you do suffer a glitch, then just turn it off then back on again.
Discussion
Comment from TheSwavu on 13 February 2019 at 00:44
Meh, the GPS rollover doesn’t affect the ability to provide accurate location data or time of day information. The real problem is that the day/month/year could be wildly wrong. However, as smart phones set their time from data received over the network this really isn’t going to be a problem.
Comment from alexkemp on 13 February 2019 at 02:01
It is not the Smartphone time that is the issue; as you say, ’phones get their time from the network, not GPS.
Clearly you do not understand GPS, else you would understand that the embedded-timestamp within the GPS-satellite server-signal is integral to all client GPS devices being able to derive their location from that signal.
Try How does GPS work?:–
Thus, the receiving device needs:
It is at #2 above that the 2¹⁰ allowance becomes an issue.
Comment from TheSwavu on 13 February 2019 at 05:37
Internally GPS works on the GPS time scale, which is the number of seconds since the epoch. All of the navigation calculations are done using the GPS time scale. The GPS time scale repeats every 19.6 years because the week number occupies only 10 bits, which means that the GPS receiver can only convert GPS time to UTC with a 19.6 year ambiguity.
This is why it is most likely that during the rollover a GPS will continue to give you correct navigation information as it doesn’t care what the current time is in UTC. It is also why the advisory from Homeland Security is addressed to “owners and operators and other users who obtain Coordinated Universal Time (UTC) from Global Positioning System (GPS) devices” and other, navigation concerned, organisations such as the FAA have not released any advisories.
To work out which particular UTC time and date it is now requires an external source of data. To do this your smart phone can just ask the network if it is currently 1980, 1998, or 2019 (or remember what the date was the last time it asked or what date it was when it was built).
Comment from Piskvor on 13 February 2019 at 09:38
@alexkemp: Actually, it doesn’t even need accurate time to begin with - that’s just a helper for obtaining a GPS fix faster. Without, the fix is still usable, but a) more satellites are needed and/or b) time to fix is increased. Old GPS receivers had no RTC clock, the GPS fix has 4 coordinates (X,Y,Z,time).
Comment from alexkemp on 13 February 2019 at 09:47
@TheSwavu:
Are you saying that only non-network connected client GPS devices greater than 20 years old will suffer problems on April 6? I certainly hope that you are right, though you may have more belief in software writers than I do.
My recall shortly after the Millennium rollover was that an analogue modem stopped working and Y2K was blamed for that by the driver supplier. I recall distinctly being boggled that (completely seriously) Y2K could stop a modem from squawking.
Comment from TheSwavu on 13 February 2019 at 10:20
The GPS receiver would also have to have been switched off for 20 years as the receivers store the last values it used so that they know when the counter has looped around.
Last time this happened it was pretty much a damp squib. Bugs do occasionally turn up GPS firmware but they are fairly rare.