5.2.2 Satellite Transmissions at 2014

The IS-GPS-200G (2012) is the authoritative source for details on the GPS signal structures, usage of these signals, and other information broadcasts by the satellites. All satellite transmissions are coherently derived from the fundamental frequency of 10.23 MHz, made available by onboard atomic clocks. This is also true for the new signals discussed further below. Multiplying the fundamental frequency by 154 gives the frequency for the L1 carrier, c05-math-0247, multiplying by 120 gives the frequency of the L2 carrier, c05-math-0248, and multiplying by 115 gives the frequency c05-math-0249. The chipping (code) rate of the P(Y)-code is that of the fundamental frequency, i.e., 10.23 MHz, whereas the chipping rate of the C/A-code is 1.023 MHz (one-tenth of the fundamental frequency). The navigation message (telemetry) is modulated on both the L1 and the L2 carriers at a chipping rate of 50 bps. It is different for modern signals as will be discussed later. It contains information on the ephemerides of the satellites, GPS time, clock behavior, and system status messages.

Onboard atomic clocks define the space vehicle time. Each satellite operates on its own time system, i.e., all satellite ...

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