Searching for "GPS protocol" reveals many sources for processed GPS data, e.g. NMEA or binary outputs of GPS units.
Where is the official documentation for the GPS satellite – receiver protocol? Or any interesting supplemental material that might explain it?
Context: I'm especially interested in learning about how (e.g.) the almanac and ephemera are transmitted.
Best Answer
The official documentation for GPS is available online at:
https://www.gps.gov/technical/
The portions you are probably most interested in are the Interface Control Documents, especially:
IS-GPS-200, "NAVSTAR GPS Space Segment / Navigation User Segment Interfaces"
IS-GPS-800, "NAVSTAR GPS Space Segment / User Segment L1C Interface"
These documents jointly define the portions of GPS used for navigation and timing. If you're specifically interested in how the almanac and epherema are transmitted, that's covered in the second document.