GPS weekcounter rollover and the Pyra mobile edition


Alphasys

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Oct 22, 2018
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On April the 6th, 2019, GPS will have a sort of Y2K-type rollover thing happening. The 10-bit weekcode will roll over from 1023 back to 0. Most recent GPS modules will have this accounted for, others require a firmware upgrade to deal with this fact. At the same time, this field in the GPS data will also be increased in bitcount.

Just putting this here to raise awareness of this, hoping the GPS modules in the Pyra Mobile edition have this accounted for. Together with any accompanying software.

Source: "How Does GPS Actually Work and Why Many GPS Devices are About to Stop Working" by "Today I Found Out" on youtube.
 

levi

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Yeah, I have a few old phones still in my drawers which no longer get any type of updated, but had GPS inbuilt, plus a bluetooth GPS module bought probably some time early in the 00s which I've never even connected to a computer and has no update buttons. I'm thinking I might be forced into a clear out, because as I understand it at the core level, GPS works by comparing time stamps to those broadcast by the connected satellites so if they're all out by ten bits then that'll never work.
 

Failbert

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Apr 18, 2017
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Not the first time it happened (see table below, notes from a lecture by my former professor Mr. George Preiss), although I don't know what happened to the functionality of any hardware (well, non-military hardware) during the 1st and 2nd "unwraps" of the week number.

upload_2019-4-3_0-49-1.png

Further very basic on how it works/why GPS is genius: A GPS receiver works by comparing a received snippet of a cycling (I'm not sure if that's the term, I'll edit if I come up with a better one) sequence from a satellite with a snippet of a sequence generated using the same parameters, based on the difference how far are they into the sequence it calculated to get the distance to dat satellite, and by doing this for a number of known and visible satellites of a known (broadcasted) position relative to Earth, it can approximate location on said Earth. It can also employ phase readings to further approximate the time difference. Early on during/after the measurement it can download corrections from reference stations (which themselves are sort-of static GPS receivers), and later we can apply further corrections based on astrological and geographical phenomena and make it accurate enough as a land surveying instrument. Very cool technology invented to precisely target nuclear weapons at my country, among others.
 
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