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GPS Network May Experience Errors in "Week Number" Rollback

posted by martyb on Tuesday March 12 2019, @12:23PM   
from the the-times-they-are-a-changin' dept.

canopic jug writes:

The American Radio Relay League (ARRL), the national association for amateur radio, has a reminder about older GPS receivers which may hit a wrap-around bug on April 6^th this year.

The GPS network will encounter a small millennium bug of its own in April when the network's "week number" rolls back to zero. This known issue especially could affect those who use GPS to obtain accurate Coordinated Universal Time (i.e., UTC). In the GPS network, the number of the current week is encoded into the message the GPS receives using a 10-bit field. This allows for weeks ranging from zero to 1023. The current period began on August 1, 1999. On April 6, 2019, the week number rolls over to zero and starts counting back up to 1023.

This should not affect later-model GPS receivers that conform to IS-GPS-200 and provide UTC, [...]

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Original Submission

• Re:Timing Re:Timing (Score: 2) by urza9814 on Tuesday March 12 2019, @05:49PM (1 child)

  by urza9814 (3954) on Tuesday March 12 2019, @05:49PM (#813385) Journal

  The real mistake in the GPS specification is making this happen every 20 years. This is too infrequent to discover any problem via testing. In hindsight, it would have been better to make the counter smaller -- say 4-5 bits or so -- so that the wraparound occurs every few months and is more likely to be noticed during a product's development cycle.

  Presumably it needs to be infrequent enough for the device to stay calibrated though....The only way I can see that the device would know how many times it's rolled over is if it's counting them and storing that in some other memory location. So if it rolls over every few months, and you only use your GPS for a long trip you take once or twice a year, you'd have to manually reset the date every single time you turned the thing on, right? Best case it calibrates against an RTC and lasts until the RTC battery dies, but then the poorly designed devices would have a non-removable RTC battery and might be useless in four or five years instead of twenty...

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• Re:Rollover (Score: 0) by Anonymous Coward on Tuesday March 12 2019, @06:48PM

  by Anonymous Coward on Tuesday March 12 2019, @06:48PM (#813412)

  Six bits is enough for a year. For an infrequently used device, telling it what year it is isn't a large hurdle.

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