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The GPS week number rollover is a phenomenon that happens every 1,024 weeks, which is about 19.6 years. The Global Positioning System (GPS) broadcasts a date, including a week number counter that is stored in only ten binary digits , whose range is therefore 0–1,023.
GPS encodes this information into the navigation message and modulates it onto both the C/A and P(Y) ranging codes at 50 bit/s. The navigation message format described in this section is called LNAV data (for legacy navigation). The navigation message conveys information of three types: The GPS date and time, and the satellite's status.
GPS dates are expressed as a week number and a day-of-week number, with the week number initially using a ten-bit value and modernised GPS navigation messages using a 13-bit field. Ten-bit systems would roll over every 1024 weeks (about 19.6 years) after Sunday 6 January 1980 (the GPS epoch ), and 13-bit systems roll over every 8192 weeks.
As opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number and a seconds-into-week number. The week number is transmitted as a ten- bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years).
Qualcomm BREW, GPS, ATSC 32-bit time stamps: GPS counts weeks (a week is defined to start on Sunday) and 6 January is the first Sunday of 1980. [35] [36] Weeks are stored in a 10-bit integer, and the first GPS week number rollover occurred in August 1999. 31 December 1989: Garmin FIT Epoch. [37]
The format does not define the source of the messages and has been used with systems as varied as longwave marine radio, communications satellite broadcasts, and internet distribution. The first widely used version of the format was released in 1990 and was based on the 30-bit long packet used by the GPS satellites, known as a "frame".
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1 odd parity bit; 1 stop bit; The on-time marker is the leading edge of the first start bit. IRIG J-1 timecode consists of 15 characters (150 bit times), sent once per second at a baud rate of 300 or greater: <SOH>DDD:HH:MM:SS<CR><LF> SOH is the ASCII "start of header" code, with binary value 0x01. DDD is the ordinal date (day of year), from 1 ...