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GPS Weel rollover.

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  • GPS Weel rollover.

    What is the GPS Week Rollover issue?

    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. 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. Each of these periods is known in GPS terms as an “epoch”.

    At the end of each epoch of 1,024 weeks, the receiver resets the week number to zero and starts counting again.

    The first GPS satellites went live on 6 January 1980, meaning that the first epoch of GPS time lasted until 21 August 1999. We are now nearing the end of the second epoch, which will fall on the 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.

    Problems could occur on or after 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. In fact, it’s much more likely that an affected receiver won’t start outputting erroneous data until long after the 6 April 2019.

    That’s because many receiver manufacturers have sought to maximise 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 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.

    For 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. This diagram shows how hard-coded pivot dates work:

    Last edited by chaccamacca; 8th March 2019, 15:09.

  • #2
    It this for all GPS systems and what about older TomTom systems?

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    • #3
      I started my TomTom Go 720 T this morning and everything was OK.So the device works like yesterday.

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