GPS Week Number Rollover (WNRO) Information

Summary: GNSS receivers that rely on Global Positioning System (GPS) face a notable event on April 6, 2019, because it marks a reset of their date information known as the GPS Week Number Rollover (GPS WNRO). Receivers that are not current with their firmware risk incorrectly reporting the GPS week which may cause additional unforeseen consequences.

Background: GPS dates are expressed as a week number and a day-of-week number, with the week number transmitted as a ten-bit value. This means that every 1024 weeks (about 19.6 years) after Sunday 6 January 1980 (the GPS epoch), the date resets again to that date; this happened for the first time at 23:59:47 on Saturday 21 August 1999 and will happen again at 23:59:42 on 6 April 2019 and on 20 November 2038.

Solution: To address this concern, modernized GPS navigation messages use a 13-bit field, which only repeats every 8,192 weeks (157 years), and will not return to zero until near the year 2137. Legacy systems with current firmware will also be unaffected. To verify you’re using the current firmware, refer to Trimble Installation Manager. All Trimble receivers with firmware version ≥2.32 will continue to operate normally following the rollover.* It is always recommended to have quality checks in place before or during the collection of data, such as checking into known control points, to ensure equipment is working properly.

*NOTE: New Trimble GNSS receivers MPS865 and SPS785 MUST use the most recent FW despite being greater than v2.32.

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