User`s guide

Appendix
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
208
Phase Observable
See Reconstructed Carrier Phase.
Point Positioning
Geographic positions produced from one receiver in stand-alone mode. At best, position
accuracy obtained from a standalone receiver is 15 to 25 meters (without SA), depending
on the geometry of the satellites.
Polar Motion
Motion of the instantaneous axis of the rotation of the earth with respect to the solid body
of the earth. This motion is irregular but more or less circular with an amplitude of about
15 miles and a main period of about 430 days (also called Chandler Wobble).
Precise Positioning Service (PPS)
The highest level of military dynamic positioning accuracy provided by GPS, based on
the dual frequency P code and having high anti jam and anti-spoof qualities.
Prime Vertical
The vertical circle perpendicular to the celestial meridian.
PRN
Pseudorandom noise, a sequence of digital ones and zeros that appear to be randomly
distributed like noise, but which can be exactly reproduced. The most significant property
of PRN codes is that they have a low autocorrelation value for all delays or lags except
when they are exactly coincident. Each NAVSTAR satellite has its own unique C/A and P
pseudorandom noise codes.
Pseudolite
A ground-based GPS transmitter station that broadcasts a signal with a structure similar
to that of an actual GPS satellite. Pseudolites are designed to improve the accuracy and
integrity of GPS, particularly near airports.
Pseudorange
A measure of the apparent propagation time from satellite to receiver antenna, expressed
as a distance. A pseudorange is obtained by multiplying the apparent signal propagation
time by the speed of light. Pseudoranges differ from actual geometric ranges due to the
satellite/receiver clock offset, propagation delays, and other errors. The apparent
propagation time is determined from the time shift required to align (correlate) a replica of
the GPS code generated in the receiver with the received GPS code. The time shift is the
difference between the time of signal reception (measured in the receiver time frame) and
the time of signal emission (measured in the satellite time frame).
Range Rate
The rate of change of range between the satellite and the receiver. The range to a
satellite changes due to both satellite and receiver motion. Range rate (or pseudorange
rate) is determined by measuring the Doppler shift of the satellite signal's carrier
frequency.