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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 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.
GPSBabel is a cross-platform, free software to transfer routes, tracks, and waypoint data to and from consumer GPS units, and to convert between GPS data formats. [2] It has a command-line interface and a graphical interface for Windows, macOS, and Linux users.
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).
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.
The timecode consists of ASCII characters, each transmitted as 10 bits: 1 start bit; 7 data bits; 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>
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RTCM Version 3, initially released in February 2004, [5] is the current and continually evolving version of the RTCM standard. In contrast to 2.3, version 3.x uses a variable-length message format and a single 24-bit cyclic redundancy check (CRC) on the entire message as opposed to a 6-bit parity for every 30-bit word.