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A-46 Lassen-SK8 Embedded GPS Module
Trimble Standard Interface Protocol
The receiver codephase resolution is 1/16th of a C/A code chip, this corresponds to:
1/16
*
C/A code chip ≈ 977.517ns/16 ≈ 61.0948 ns
≈ 61.0948
*
speed of light, m/s
≈ 18.3158 meter
The integer millisecond portion of the pseudo-range must then be derived by utilizing the
approximate user and satellite positions. Rough user position (within a few hundred
kilometers) must be known; the satellite position can be found in its almanac / ephemeris
data.
Each mS integer corresponds to:
C/A code epoch
*
speed of light = 1 ms
*
speed of light, m/s
≈ 300km
(approx.)
≈ 299.792458 km (precise)
The satellite time-of-transmission for a measurement can be reconstructed using the code
phase, the time of measurement, and the user-determined integer number of milliseconds.
*
Note – The receiver occasionally adjusts its clock to maintain time accuracy within 1
msec. At this time, all pseudorange values for all satellites are adjusted upward or
downward by one millisecond. Message 0x6F shows this clearly; it is hidden in 0x5A.