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What data is transmitted by GPS satellites?
Each GPS satellite broadcasts a continuous stream of data that's broken up into segments transmitted over 30 seconds. Each of these 30 second frames includes the following information:
- status of the transmitting satellite
- clock / time data
- ephemeris data (describes the location of the transmitting satellite)
- almanac data (describes the orbits of all GPS satellites)
GPS satellites transmit data at 50 bits per second. This is much slower than a computer modem but fast enough to update your location several times per second (once satellites have been acquired).
Data needed to begin using a satellite for position calculations is included in every 30 second frame (clock and ephemeris data).
Almanac data, which is too long to fit within a single frame, is divided into chunks and spread across 25 frames (taking 12½ minutes to transmit).
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