NAVIOR-24S
™
Appendix G
Glossary
227
NAVIOR-24S ™
Revision
V1.00 20.05.2008
elevation drops below the mask.
ROM Read-Only
Memory.
RS-232
A communication standard for digital data. Specifies a number of signal
and control lines. RS-232 is often associated with a 9 pin connector
called a DB-9
RTCM
Radio Technical Commission for Maritime Services. Commission that
recommends standards for differential GPS services. “RTCM
Recommended Standards For Differential GPS Service,” prepared by
RTCM Special Committee No. 104 (RTCM SC-104), defines a
communication protocol for sending GPS differential corrections from a
differential reference station to remote GPS receivers.
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/GLONASS 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/GLONASS signal is a wide bandwidth, low-power
signal (-160dBW). 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 multipath.