![]() ![]() The exact time at which these kind of problems will occur depends on the GPS receiver model and firmware version, and is not related to the GPS system-specific rollover dates mentioned above. This has happened with some 3rd party GPS receivers in February 2016, and some other 3rd party GPS receivers are expected to have problems after July, 2016. Instead, it can occur at an arbitrary weekend when the number reaches the threshold determined by the firmware developers. The worst thing with this approach is that this switchback doesn't occur at the same time as the scheduled week number rollover in the satellite data. 1884 for the extended week number, but after real week number 1884 the calculation yields a number in the range 0.860, thus a wrong date 1024 weeks in the past. If you take 90 as a limit the resulting range would be 1990.2089.įor the GPS week number example this results in a valid range like 860. GPS WEEK NUMBER FULLThis approach is similar to extending a 2 digit year number to a full 4 digit year number. ![]() If the week number is above 860 we assume a rollover has not yet occurred.” “If the transmitted week number is below 860 we assume a rollover has already occurred, and thus add 1024 to get a full week number. There are 3rd party GPS receivers out there which take a very simply approach with a fixed week number limit, e.g.: ![]() The first GPS week number rollover occured 1024 weeks later, on Saturday, 21st August 1999, and the next rollover occured another 1024 weeks later, on Saturday, 6th April 2019.įor pure navigational receivers this doesn't matter much since they work based on time differences only, but GPS receivers used for time synchronization have to properly account for these rollovers to determine the correct calendar date.Īll Meinberg devices with integrated GPS or GNSS receivers handle the week number rollovers without problems.Ī more detailed explanation follows below. The “start date” of the GPS system time is Sunday, 6th January 1980. This behavior is intentional and has been clearly specified in the GPS Interface Control Document Unfortunately most GPS satellites send the GPS week number encoded in 10 bits only, covering a range of 1024 weeks (week numbers 0 through 1023), and after week 1023 the week number transmitted by the satellites rolls over to 0. Topcon has released new firmware for this receiver to correctly handle the rollover.Įvery manufacturer is advising that you ensure that every device has the most up-to-date firmware available installed.įor details on the resources made available by the primary high-precision GPS hardware manufacturers detailing their concerns visit UNAVCO.The GPS system time is based on week numbers since an epoch, and seconds of the current week. Note that the receiver is displaying UTC, which differs from GPS time by 18-seconds. GPS WEEK NUMBER SIMULATORHere is a 1-minute video from UNAVCO’s simulator tests demonstrating the improper behavior of a Topcon GB-1000 GNSS receiver with an older firmware version during the rollover. Critical systems should be actively monitored during and after the rollover to ensure continued operation. GPS WEEK NUMBER SOFTWAREAlso ensure that any software systems that use real-time streams from suspect hardware are capable of handling bad date stamps. The best courses of action are to ensure that firmware is updated for every device that requires it and has available updates, or to replace any hardware that cannot be updated. And while any incorrectly time-stamped data files MIGHT be recoverable using translation software for post-processing, this has not yet been confirmed. Simulator testing conducted by UNAVCO and many others has shown that satellite tracking, position solutions and other functions would continue, so the devices would not fail, but any system that relies on the time stamps produced by those devices might. The primary symptom of a device that doesn’t handle the rollover correctly would be that any data logged or streamed would be time stamped by 19.7 or 39.4 years in the past, i.e. may also require firmware updates or hardware replacement in order to properly handle the rollover.įurthermore it’s possible that the effects of the rollover may not be immediately noticed on, but later if improper methods are used in firmware to adjust the date. In addition to the high-precision receivers such as seismometers, dataloggers, cellular modems, internet routers, etc. As the gps.gov presentation states, the best course of action for all owners of GPS receivers and any other hardware that uses GPS for timing or geolocation is to “Trust but Verify” by directly contacting the manufacturer of any such hardware for advice. ![]()
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