Trimble Standard Interface Protocol

A

Time of measurement

The time of measurement (Byte 17) is the center of the sample interval adjusted by adding the receiver-supplied codephase (modulo mS) to a user-determined integer number of mS between user and satellite.

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 meters

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

=

300 km (approximate)

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.

0x5B Report Packet 5B

Satellite Ephemeris Status Report

This packet is sent in response to packet 3B and optionally, when a new ephemeris (based on IODE) is received. It contains information

A-66

Acutime 2000 Synchronization Kit User Guide

Page 172
Image 172
Trimble Outdoors Part Number 45005-00-ENG Satellite Ephemeris Status Report, Time of measurement, 0x5B Report Packet 5B