What You Need to Know About the 2019 GPS Rollover
It’s hard to believe that it’s been nearly 20 years since the turn of the millennium. It seems like just yesterday that we were prepping for the inevitable global disaster that was Y2K. Back then, electric cars were still a dream, the Galileo constellation was still just a “plan”, mobile phones were bricks with miniature monochrome screens and the idea of an internet connection on a phone was like science fiction. However, one important moment in 1999 directly affected our industry - the first GPS epoch week rollover.
What is the epoch week rollover? To answer that we’ll need to go over some of the basics. The Global Positioning System (GPS) provides accurate timing and positioning information to many crucial industries and services in everyday life. It also has its own date and time scale that expresses the current week number and the current number of seconds within a week. This allows the receiver to translate the supplied information into an accurate format that presents the time of day, day, month and year. To restrict the size of the data that is transmitted by the satellite, the GPS Week Number is a 10-bit binary code. This limits the range of the GPS Week Number to 0-1023 or 1024 weeks in total. This 1024-week duration is known as an epoch, and at the end of each epoch the week number rolls over and resets the week number to zero, starting the process over again.
GPS week zero originally began on January 6th, 1980 and incremented for the next 1024 weeks until the counter ran out and rolled over on August 21st, 1999. Based on the binary number limitations, the next epoch week rollover will take place on April 6th, 2019. This means from that date onward, it is likely to start seeing rollover problems in GPS receivers that aren’t programmed to cope with the week number reset.
Fortunately, over the last 20 years, NovAtel® has designed products with this rollover in mind. As previously mentioned, this will be the second era rollover since GPS was established and in preparation, NovAtel has thoroughly tested our OEM4 through OEM7® receivers in multiple scenarios using commercially available GPS simulators to ensure that our products will function properly on April 6, 2019.
The tests we conducted were completed with no operational problems and we don’t expect any user issues when the rollover date occurs. All NovAtel OEM4 (version 2.322) through OEM7 commercial receivers will continue to increment the week number from 2047 to 2048 and operate as expected both during and after the rollover. We did note one issue on OEM6 receivers with firmware < 6.510, OEMStar, OEMV and OEM4 with the RAWALM log, however, the ALMANAC log does not have an issue. If you are using the RAWALM log on any of these systems, please refer to our GPS Week Rollover Service Bulletin for additional information.