Viavi 87339, Руководство по эксплуатации

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C/A Code
The standard (Clear/Acquisition) GPS PRN code, also known as the
Civilian Code or S-Code. A spread spectrum direct sequence code only
modulated on the L1 carrier, used by the GPS receiver to acquire and
decode the L1 satellite signal, and from which the L1 pseudo-range
measurement is made.
Carrier A radio wave having at least one characteristic (e.g., frequency,
amplitude, phase) that can be varied from a known reference value by
modulation. In the case of GPS there are two transmitted carrier waves:
(a) L1 at 1575.42MHz, (b) L2 at 1227.60MHz, modulated by the
Navigation Message (both L1 and L2), the P-Code (both L1 and L2) and
the C/A-Code (L1).
Carrier Phase
GPS measurements made on the L1 or L2 carrier signal. May refer to
the fractional part of the L1 or L2 carrier wavelength (approximately
19cm for L1, 24cm for L2), expressed in units of meters, cycles, fraction
of a wavelength or angle. (One cycle of L1 is equivalent to one
wavelength, and similarly for L2.) In carrier phase-based positioning,
such as employed in GPS Surveying techniques, carrier phase may also
refer to the accumulated or integrated measurement which consists of
the fractional part plus the whole number of wavelengths (or cycles)
since signal lock-on.
Carrier Aided Tracking A signal processing strategy that uses the GPS carrier signal to achieve
an exact lock-on the PRN code. More efficient and accurate than the
standard approach.
Clock Bias
The difference between the receiver or satellite clock's indicated time
and a well-defined time scale reference such as UTC (Coordinated
Universal Time), TAI (International Atomic Time) or GPST (GPS Time).
Chip One bit of a spreading sequence.
Channel
A single satellites signal on a single frequency.
Code Phase GPS measurements based on the C/A-Code. The term is sometimes
restricted to the C/A- or P-Code pseudo-range measurement when
expressed in units of cycles.
Constellation
Refers to either the specific set of satellites used in calculating a
position, or all the satellites visible to a GPS receiver at one time, or the
entire ensemble of GPS satellites comprising the Space Segment.
Control Segment A world-wide network of GPS monitoring and upload telemetry stations
operated by, or on behalf of, the US Department of Defense. The
tracking data is used by the Master Control Station at Colorado Springs
to calculate the satellites' positions (or "broadcast ephemerides") and
their clock biases. These are formatted into the Navigation Message
which is uploaded on a daily (perhaps more frequently) basis by the
Control Segment stations.
Correlator
The GPS receiver "software" or electronic means, implemented in some
fashion (either analogue or digital) within a Tracking Channel, used to
shift or compare the incoming signal with an internally generated signal.
This operation is performed on the PRN codes, but may be used for
more "exotic" mixed signals in the case of L2 measurements, where
under the policy of Anti-Spoofing (AS) the L2 PRN code is not known.
Correlator design may be influenced such that it is optimized for
accuracy, mitigation of multi-path, acquisition of signal under foliage,
etc.
Cut Off Angle The minimum acceptable satellite elevation angle (above the horizon) to
avoid blockage of line-of-sight, multi-path errors or too high
Tropospheric or Ionospheric Delay values. May be preset in the
receiver, or applied during data post-processing. For navigation
receivers may be set as low as 5°, while for GPS Surveying typically a
cutoff angle of 15° is used.
Term Description