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Acutime 2000 Synchronization Kit User Guide Glossary-11
Glossary
satellite masks As satellites approach the horizon, their signals can become
weak and distorted, preventing the receiver from gathering
accurate data. Satellite masks enable you to establish criteria
for using satellite data in a position solution. There are three
types of satellite masks: Elevation, SNR, and PDOP.
SA Selective Availability. This is the name of the policy and the
implementation scheme by which unauthorized users of
GPS will have their accuracy limited to 100 meters 2D RMS
horizontal and 156 meters 2D RMS vertical.
SEP Spherical Error Probability. The radius of a sphere such that
50% of the position estimates will fall within the surface of
the sphere.
serial
communication
A system of sending bits of data on a single channel one
after the other, rather than simultaneously.
serial port A port in which each bit of information is brought in/out on
a single channel. Serial ports are designed for devices that
receive data one bit at a time.
signal-to-noise
level
GPS signals with SNRs that do not meet the mask criteria
are considered unusable.
signal-to-noise
ratio
A measure of the relative power levels of a communication
signal and noise on a data line. SNR is expressed in decibels
(dB).
SNR Signal-to-Noise Ratio.
spread spectrum The received GPS signal is a wide bandwidth, low-power
signal (-160 dBW). This property results from modulating
the L-band signal with a PRN code in order to spread the
signal energy over a bandwidth which is much greater than
the signal information bandwidth. This is done to provide
the ability to receive all satellites unambiguously and to
provide some resistance to noise and multi-path.