User`s guide

Appendix
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
200
Code Division Multiple Access (CDMA)
A method of frequency reuse whereby many radios use the same frequency but with
each one having a separate and unique code. GPS uses CDMA techniques with Gold
codes for their unique cross-correlation properties.
Cold Start
Typical time a GPS receiver requires to develop a fix after application of power given that
the receiver has no stored data. Cold starts times normally have a large standard
deviation as the time depends heavily on satellite visibility at any given time.
Conventional International Origin (CIO)
Average position of the earth's rotation axis during the years 1900-1905.
Correlation-Type Channel
A GPS receiver channel that uses a delay-lock-loop (DLL) to maintain an alignment
(correlation peak) between the replica of the GPS code generated in the receiver and the
received code from the satellite.
Deflection of the Vertical
The angle between the normal to the ellipsoid and the vertical (true plumb-line). Since
this angle has both a magnitude and a direction, it is usually resolved into two
components: one in the meridian and the other perpendicular to it in the prime vertical.
Delay-Lock-Loop
The technique whereby the received code (generated by the satellite clock) is compared
with the internal code generated by the receiver clock. The latter is shifted in time until
the two codes match. Delay-lock-loops can be implemented in several ways, including
tau dither and early-minuslate gating.
Delta Pseudorange
See Reconstructed Carrier Phase.
Differential Processing
GPS measurements can be differenced between receivers, satellites, and epochs.
Although many combinations are possible, the present convention for differential
processing of GPS measurements are to first take differences between receivers (single
difference), then between satellites (double difference), then between measurement
epochs (triple difference).
A single-difference measurement between receivers is the instantaneous difference in
phase of the signal from the same satellite, measured by two receivers simultaneously.
A double-difference measurement is obtained by differencing the single difference for one
satellite with respect to the corresponding single difference for a chosen reference
satellite.