GPS and Y2K Deja Vu

Quote of the Day

There is something to be said for cold, calculating competence.

Morning Joe TV program gave this review of the movie Vice and its portrayal of Dick Cheney.


Figure 1: GPS-III-A satellite.

Figure 1: GPS-III-A satellite. (Source: US Government)

I have been working since May 2018 as a contractor for various companies on resolving specific issues – I am a troubleshooter. This role has provided me with a number of interesting challenges. One of my recent challenges is helping folks deal with the GPS Week Number Rollover (WNRO) issue.  This issue involves a 10-bit week counter that has been counting up from 0 every week since 21-August-1999.  This counter can will count up to 1023 and then it will rollover to 0 on 7-April-19. Not everyone is prepared for this rollover. This issue shares many similarities with the Y2K problem. See this presentation for a good overview of the rollover issue.

These 1024 week intervals are referred to as epochs. Each epoch lasts 19 years, 7 months, and 15 days. GPS went live on 6 - Jan-1980 and the first epoch ended on 20-Aug-1999. We are now in the second GPS epoch and the 3rd epoch begins 7-April-2019.

Going forward, GPS implementations will be using 13-bit counters, which will reduce the frequency of these events.

We can easily use Excel to show that the next rollover date is 7-April-2019.


I  swear that I deal with these counter rollover issues at least once a year (earlier example).

 
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One Response to GPS and Y2K Deja Vu

  1. Joel Lagerquist says:

    And there is the upcoming Unix epoch roll-over in 2038.

     

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