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Bandwidth — The range of frequencies in a signal.
Bearing — the horizontal direction of one terrestrial point from anther terrestrial point, expressed as the
angular distance from a reference direction, usually measured from 000° at the reference direction
clockwise through 360°. The reference point may be True North, Magnetic North, or Relative (ship's
head).
Carrier — the steady transmitted RF signal whose amplitude, frequency, or phase may be modulated to carry
information.
Carrier Phase Ambiguity (or sometimes ambiguity for short) — the number of integer carrier phase cycles
between you and the satellite at the start of tracking.
Carrier phase measurements — these are "accumulated delta range" measurements. They contain the
instantaneous phase of the signal (modulo 1 cycle) plus some arbitrary number of integer cycles.
Once the receiver is tracking the satellite, the integer number of cycles correctly accumulates the
change in range seen by the receiver. When a "lock break" occurs, this accumulated value can jump
an arbitrary integer number of cycles (this is called a cycle slip).
CEP — circular error probable; a circle's radius, centered at the true antenna position, containing 50 percent
of the points in the horizontal scatter plot.
Channel — A channel of a combined GPS/GLONASS receiver consists of the circuitry necessary to receive
the signal from a single GPS/GLONASS satellite.
Checksum — by NMEA standard, a validity check performed on the data contained in the sentences,
calculated by the talker, appended to the message, then recalculated by the listener for comparison
to determine if the message was received correctly. Required for some sentences, optional for all
others.
Circular Error Probable (CEP) — the radius of a circle, centered at your true location, that contains 50
percent of the individual position measurements made using a particular navigation system.
Clock Bias — The difference between the clock's indicated time and true universal time.
Clock Offset — Constant difference in the time reading between two clocks.
Coarse Acquisition (C/A) Code — a spread spectrum direct sequence code that is used primarily by
commercial GPS receivers to determine the range to the transmitting GPS satellite. Uses a chip rate
of 1.023 MHz. Also known as the "civilian code."
Communication protocol — a method established for message transfer between a talker and a listener which
includes the message format and the sequence in which the messages are to be transferred. Also
includes the signalling requirements such as bit rate, stop bits, parity, and bits per character.
Control segment — the Master Control Station and the globally dispersed reference Stations used to manage
the satellites, determine their precise orbital parameters, and synchronize their clocks. GLONASS
and GPS have their own control segments and use their own time for determining clock offset.
Course — the horizontal direction in which a vessel is to be steered or is being steered; the direction of travel
through the air or water. Expressed as angular distance from reference North (either true, magnetic,
compass, or grid), usually 000° (north), clockwise through 360°. Strictly, the term applies to
direction through the air or water, not the direction intended to be made good over the ground (see
track, Page 122). Differs from heading.
Course Made Good (CMG) — the single resultant direction from a given point of departure to a subsequent
position; the direction of the net movement from one point to the other. This often varies from the
track caused by inaccuracies in steering, currents, cross-winds, etc. This term is often considered to
be synonymous with Track Made Good, however, track made good is the more correct term.
Course Over Ground (COG) — the actual path of a vessel with respect to the Earth (a misnomer in that
courses are directions steered or intended to be steered through the water with respect to a reference
meridian); this will not be a straight line if the vessel's heading yaws back and forth across the course.
Crab — the apparent sideways motion of an aircraft with respect to the ground when headed into a crosswind.
GPS/GLONASS Receiver User Manual Rev 1
I GPS/GLONASS Glossary of Terms
115
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