User`s guide

Appendix
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
207
NAVSTAR
The acronym given to GPS satellites, which stands for NAVigation Satellite Timing And
Ranging.
Observation Session
The period of time over which simultaneous GPS data is collected by two or more
receivers.
Outage
A point in time and space that the GPS receiver is unable to compute a position fix. This
may be due to satellite signal blockage, unhealthy satellites, or a dilution of precision
(DOP) value that exceeds a specified limit.
P-Code
The protected or precise code modulated on both the L1 and L2 GPS signals. The P-
Code is a very long (about 1014 bits) sequence of pseudorandom binary bi-phase
modulations on the GPS carrier at a chipping rate of 10.23 MHz that does not repeat
itself for about 38 weeks. Each satellite uses its own unique one-week segment of this
code, which is reset each week. Under anti-spoofing, the P-Code is encrypted to form Y
code. The Y code is only accessible by authorized users, as controlled by the U.S.
Department of Defense.
PDOP
Position dilution of precision, a unitless figure of merit expressing the relationship
between the error in user position and the error in satellite ranges. Geometrically, PDOP
is proportional to the inverse of the volume of the pyramid formed by lines running from
the receiver to four observed satellites. Values considered good for positioning are small,
such as 3 or less. Values greater than 7 are considered poor. Small PDOP is associated
with many or widely separated satellites, and large PDOP is
associated with bunched up or few satellites. See Dilution of Precision.
Parity Error
A digital message consists of ones and zeros. Parity is an Exclusive-Or sum of these bits
in a word unit. A parity error results when a bit (or bits) is changed during transmission,
so that the parity calculated at reception is not the same as it was when the message
was transmitted.
Perigee
That point in a geocentric orbit when the geometric distance is at a minimum. The closest
approach of the orbiting body.
Phase-Lock-Loop
The technique of making the phase of an oscillator signal follow exactly the phase of a
reference signal. This is accomplished by first comparing the phases of the two signals,
and then using the resulting phase difference signal to adjust the reference oscillator
frequency to eliminate phase difference when the two signals are next compared.