C-Nav Hardware Reference Guide
96
or more objects—the ground, a vehicle, boat, building or some other surface—and once
received by the antenna, will yield a larger pseudo-range estimate and increase the error.
Multipath Error is a positioning error resulting from interference between radio waves that has
traveled between the transmitter and the receiver by two paths of different electrical lengths.
Navigation Code uses the two GPS carrier waves and operates on a very low frequency (about
50Hz). This code communicates the GPS message (a string of data) from the GPS satellites to
the GPS receivers on L1 and L2 carrier waves.
Navigation (.YYn) files one of the three file types that make up the RINEX file format. Where
YY indicates the last two digits of the year the data was collected. A navigation file contains
satellite position and time information.
Navigation Message is the 1500-bit message broadcast by each satellite at 50bps on both L1
and L2 beacons. This message contains system time, clock correction parameters, ionospheric
delay model parameters, and the vehicle’s ephemeris and health. This information is used to
process the GPS signal to obtain user position and velocity.
NAVSTAR is the name given to GPS satellites, originally manufactured by Rockwell
International.
Observation (.YYo) files one of the three file types that make up the RINEX file format. Where
YY indicates the last two digits of the year the data was collected. An observation file contains
raw GPS position information.
P-code is the extremely long pseudo-random code generated by a GPS satellite. It is intended
for use only by the U.S. military, so it can be encrypted to Y-code, and then denies unauthorized
users access.
Parity is a method of detecting communication errors by adding an extra parity bit to a group of
bits. The parity bit can be a 0 or 1 value so that every byte will add up to an odd or even number
(depending on whether odd or even parity is chosen).
PDOP Mask is the highest PDOP value at which a receiver computes positions.
Perigee is the point in the orbit of a satellite about the earth that is the least distant from the
center of the earth.
Phase Center is the point in an antenna where the GPS signal from the satellites is received.
The height above ground of the phase center must be measured accurately to ensure accurate
GPS readings. The phase center height can be calculated by adding the height to an easily
measured point, such as the base of the antenna mount, to the known distance between this
point and the phase center.
Phase Lock is the technique where the phase of a signal is set to replicate the phase of a
reference signal by comparing the phase of the two signals and then using the resultant phase
difference to adjust the reference oscillator to eliminate the difference.
Phase Measurement is measurement expressed as a percentage of a portion of a wave (e.g. a
sine wave). For example, a complete wavelength
Position is the latitude, longitude, and altitude of a point. An estimate of error is often
associated with a position.
Position Dilution of Precision (PDOP) is a measure of the magnitude of Dilution of Position
(DOP) errors in the x, y, and z coordinates.
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