Satellite dictionary of Terms &
Definitions
To Setup or move your Dish you Will need to know what some of these terms mean.
ACTS Communications Technology Satellite. A NASA experimental satellite
project to
demonstrate the use of the Ka-Band (30/20 GHz) services.
Advanced
Communications Technology Satellite. A NASA experimental satellite
project to
demonstrate the use of the Ka-Band (30/20 GHz) services.
A/D Conversion - (analog-to-digital conversation) The process of converting a time-continuous analog signal to a sampled digital representation.
Adaptive - Refers to the ability of the DCLZ algorithm to "adapt" or change to accommodate differences in the type of data to be compressed.
Algorithm - Systematic means of describing a problem; a procedure for solving a problem in a finite number of steps.
Amplitude Shift Keying- A digital modulation format where information is conveyed in the amplitude of a carrier signal.
Amplitude Modulation (AM)
The
baseband signal is caused to vary the amplitude or height of the carrier
wave to
create the desired information content.
Analog - Analog refers to electronic transmission accomplished by adding signals of varying frequency or amplitude to carrier waves of a given frequency of alternating electromagnetic current. Broadcast and phone transmission have conventionally used analog technology. A modem is used to convert analog to digital information to and from your computer.
Asymmetrical links - are ideal for data based communications such as web browsing due to the limited need for uplink and the high need for downlink to display pages. Ideally, bandwidth for web browsing should be assigned to the network asymmetrically as there should be little or no need to provide and pay for the same bandwidth for inbound delivery as is needed for the outbound. Unlike terrestrial networks, with satellite links it is possible to assign bandwidth exactly as required for each direction
Analog-to-Digital Conversion (ADC)
Process of converting analog signals to a digital
representation. DAC
represents the reverse translation.
Automatic Repeat Request - (ARR) Protocol for dealing with data words that are corrupted by errors whereby the receiving system requests a re-transmission of the word(s) in error.
ANIK
The Canadian
domestic
satellite system that transmits Canadian Broadcasting Corporation's
(CSC)
network feeds throughout the country. This system also carries long
distance
voice and data services throughout Canada as well as some transborder
service to
the U.S. and Mexico.
Antenna
A device
for
transmitting and receiving radio waves. Depending on their use and
operating
frequency, antennas can take the form of a single piece of wire, a
di-pole a
grid such as a yagi array, a horn, a helix, a sophisticated
parabolic-shaped
dish, or a phase array of active electronic elements of virtually any
flat or
convoluted surface.
Aperture
A cross
sectional area
of the antenna which is exposed to the satellite signal.
Apogee
The point in
an
elliptical satellite orbit which is farthest from the surface of the
earth.
Geosynchronous satellites which maintain circular orbits around the
earth are
first launched into highly elliptical orbits with apogees of 22,237
miles. When
the communication satellite reaches the appropriate apogee, a rocket
motor is
fired to place the satellite into its permanent circular orbit of 22,237
miles.
Apogee Kick Motor (AKM)
Rocket
motor fired to circulate orbit and deploy satellite into geostationary
orbit.
Apstar (Asia-Pacific Star)
Name of the
Chinese
satellite system which carries commercial video services in the
region.
Arabsat
This is the Arabsat Satellite
Organization and
its is headquartered in Riyadh, Saudi Arabia. It provides regional
telecommunications services for the Middle East
region.
AsiaSat
A satellite system covering the Asia
mainland.
Asynchronous Communications
Stream of data
routed
through a network as generated, rather than in organized message blocks.
Most
personal computers send data in this format. (See ATM)
Asynchronous Transfer Mode (ATM)
This is the
new form
of super-fast packet switching operating at speeds in the
Gigabits/second.
Attenuation
The
loss in power
of electromagnetic signals between transmission and reception
points.
Attitude Control
The
orientation of the satellite in relationship to the earth and the
sun.
Audio Subcarrier
The carrier between 5 MHz and 8 MHz containing audio (or voice) information inside of a video carrier.
Automatic Frequency Control (AFC)
A circuit which automatically controls the frequency of a
signal.
Automatic Gain Control (AGC)
A
circuit which automatically controls the gain of an amplifier so that
the output
signal level is virtually constant for varying input signal
levels.
AZ/EL Mount
Antenna
mount that
requires two separate adjustments to move from one satellite to
another;
Azimuth
The angle
of rotation
(horizontal) that a ground based parabolic antenna must be rotated
through to
point to a specific satellite in a geosynchronous orbit. The azimuth
angle for
any particular satellite can be determined for any point on the surface
of the
earth giver the latitude and longitude of that point. It is defined with
respect
to due north as a matter of easy convenience.
Bandwidth - The number of cycles per second expressing the difference between limiting frequencies of a band; in digital systems, the measure of the amount of information that can be processed per unit time.
BCH - A type of block coding of data words named after the inventors Bose, Chaudhuri and Hocquenghem.
8PSK – 8 Phase-Shift Key – data modulation is performed to the bits from the output of the physical channel mapping procedure. Modulation 3 consecutive binary bits are represented by one complex valued data symbol. 8PSK deals with bandwidth by reducing spectral occupancy compared to lower order modulation methods.
BER – Bit Error Rate - In a digital transmission, BER is the percentage of bits with errors divided by the total number of bits that have been transmitted, received or processed over a given time period. The rate is typically expressed as 10 to the negative power. For example, four erroneous bits out of 100,000 bits transmitted would be expressed as 4 x 10 -5, or the expression 3 x 10 -6 would indicate that three bits were in error out of 1,000,000 transmitted. BER is the digital equivalent to signal-to-noise ratio in an analog system.
BERT – Bit Error Rate Test - a procedure or device that measures the bit error rate of a transmission.
Block Codes - A code with a fixed number of bytes.
Broadband - Describing transmission equipment and media that can support a wide range of electromagnetic frequencies; typically, the technology of Cable Antenna Television transmissions, as applied to data communications, that employs coaxial cable as the transmission medium and radio frequency carrier signals in the 50- to 500- MHz range; any communication channel with bandwidth greater than that of a voice-grade telecommunications channel; sometimes used synonymously with wideband.
Bandwidth 2
A measure
of spectrum
(frequency) use or capacity. For instance, a voice transmission by
telephone
requires a bandwidth of about 3000 cycles per second (3KHz). A TV
channel
occupies a bandwidth of 6 million cycles per second (6 MHz) in
terrestrial
Systems. In satellite based systems a larger bandwidth of 17.5 to 72 MHz
is used
to spread or "dither" the television signal in order to prevent
interference.
Buffer - A temporary storage space in a computer system or subsystem; especially one that accepts data at one rate and delivers it at another (to coordinate subsystems that process data at different rates).
Byte - Digital word containing eight information bits (1's or 0's).
B-Mac
A method of
transmitting
and scrambling television signals. In such transmissions MAC
(Multiplexed Analog
Component) signals are time-multiplexed with a digital burst containing
digitized sound, video synchronizing, authorization, and
information.
Backhaul
A
terrestrial
communications channel linking an earth station to a local switching
network or
population center.
Backoff
The process
of reducing
the input and output power levels of a traveling wave tube to obtain
more linear
operation.
Band Pass Filter
An
active or
passive circuit which allows signals within the desired frequency band
to pass
through but impedes signals outside this pass band from getting
through.
Baseband
The basic
direct
output signal in an intermediate frequency based obtained directly from
a
television camera, satellite television receiver, or video tape
recorder.
Baseband signals can be viewed only on studio monitors. To display the
baseband
signal on a conventional television set a "modulator" is required to
convert the
baseband signal to one of the VHF or UHF television channels which the
television set can be tuned to receive.
Baud
The rate of
data
transmission based on the number of signal elements or symbols
transmitted per
second. Today most digital signals are characterized in bits per
second.
Beacon
Low-power
carrier
transmitted by a satellite which supplies the controlling engineers on
the
ground with a means of monitoring telemetry data, tracking the
satellite, or
conducting propagation experiments. This tracking beacon is usually a
horn or
omni antenna.
Beamwidth
The angle
or conical
shape of the beam the antenna projects. Large antennas have narrower
beamwidths
and can pinpoint satellites in space or dense traffic areas on the earth
more
precisely. Tighter beamwidths thus deliver higher levels of power and
thus
greater communications performance.
Bird
Slang for a
communications
satellite located in geosynchronous orbit.
Bit
A single
digital unit of
information
Bit Error Rate
The
fraction of
a sequence of message bits that are in error. A bit error rate of 10-6
means
that there is an average of one error per million bits.
Bit Rate
The speed
of a digital
transmission, measured in bits per second.
Blanking
An
ordinary television
signal consists of 30 separate still pictures or frames sent every
second. They
occur so rapidly, the human eye blurs them together to form an illusion
of
moving pictures. This is the basis for television and motion picture
systems.
The blanking interval is that portion of the television signal which
occurs
after one picture frame is sent and before the next one is transmitted.
During
this period of time special data signals can be sent which will not be
picked up
on an ordinary television receiver.
Block Down Converter
A device
used to convert the 3.7 to 4.2 KHz signal down to UHF or lower
frequencies (1
GHz and lower).
BPSK (Binary Phase Shift Keying)
A digital
modulation
technique in which the carrier phase can have one of two possible
values, namely
0 degrees or 180 degrees.
Broad
beam
A single large circular beam that covers a large
geographic
area
Broadcast
The
sending of one
transmission to multiple users in a defined group (compare to
unicast).
BSS (Broadcast Satellite Service)
This is
the ITU
designation but DBS or Direct Broadcast Service is more
commonly used term
in the satellite industry.
Business
Television
Corporate
communications tool involving video transmission of information via
satellite.
Common uses of business television are for meetings,
product
introductions and training.
Buttonhook Feed
A shaped
piece of
waveguide directing signal from the feed to the LNA behind the
antenna.
Bypass
Use of satellite, local area network,
wide area
network or metropolitan area network as an alternative transmission
facility.
C Band
This is the
band between
4 and 8 GHz with the 6 and 4 GHz band being used for satellite
communications.
Specifically, the 3.7 to 4.2 GHz satellite communication band is used as
the
down link frequencies in tandem with the 5.925 to 6,425 GHz band that
serves as
the uplink.
Carrier
The basic
radio,
television, or telephony center of frequency transmit signal. The
carrier in an
analog signal. is modulated by manipulating its amplitude (making it
louder or
softer) or its frequency (shifting it up or down) in relation to the
incoming
signal. Satellite carriers operating in the analog mode are usually
frequency
modulated.
Carrier Frequency
The main
frequency on which a voice, data, or video signal is sent. Microwave and
satellite communications transmitters operate in the band from 1 to 14
GHz (a
GHz is one billion cycles per second).
Carrier to Noise Ratio (C/N)
The ratio of the received carrier power and the noise power in
a given
bandwidth, expressed in dB. This figure is directly related to G/T and
S/N; and
in a video signal the higher the C/N, the better the received
picture.
Cassegrain Antenna
The antenna
principle that utilizes a subreflector at the focal point which reflects
energy
to or from a feed located at the apex of the main reflector.
CATV
Originally meant Community Antenna
Television.
Independent smaller companies in rural communities would build a
large
television receiving antenna on a nearby mountain to pick up the weak TV
signals
from a distant metropolis. These signals were amplified, modulated onto
television channels and sent along a coaxial cable strung from house to
house.
CCITT (now TSS)
Comite Consultatif
Internationale de
Telegraphique et Telephonique. International body, associated with the
ITU,
which establishes worldwide standards for telecommunications.
Reorganized to
include CCIR (radio standards group) and renamed TSS (Telecommunications
Standardization Sector).
CDMA
Code division
multiple
access. Refers to a multiple-access scheme where stations use
spread-spectrum
modulations and orthogonal codes to avoid interfering with one
another.
Channel
A frequency
band in
which a specific broadcast signal is transmitted. Channel frequencies
are
specified in the United States by the Federal Communications Commission.
Television signals require a 6 MHz frequency band to carry all the
necessary
picture detail.
CIF
Common Intermediate Format. A compromise
television display format adopted by the CCITT which is relatively easy to
derive from both PAL and NTSC.
Circular Polarization
Unlike
many domestic satellites which utilize vertical or horizontal
polarization, the
international Intelsat satellites transmit their signals in a rotating
corkscrew-like pattern as they are down-linked to earth. On some
satellites,
both right-hand rotating and left-hand rotating signals can be
transmitted
simultaneously on the same frequency; thereby doubling the capacity of
the
satellite to carry communications channels.
Clamp
A video
processing
circuit that removes the energy dispersal signal component from the
video
waveform.
Clarke Orbit
That
circular
orbit in space 22,237 miles from the surface of the earth at which
geosynchronous satellites are placed. This orbit was first postulated by
the
science fiction writer Arthur C. Clarke in Wireless World magazine in
1945.
Satellites placed in these orbits, although traveling around the earth
at
thousands of miles an hour, appear to be stationary when viewed from a
point on
the earth, since the earth is rotating upon its axis at the same angular
rate
that the satellite is traveling around the earth.
C/No or C/kTB
Carrier-to-noise
ratio measured either at the Radio Frequency (RF) or Intermediate
Frequency
(IF).
Coaxial Cable
A transmission line in which
an inner
conductor is surrounded by an outer conductor or shield and separated by
a
nonconductive dielectric.
Codec
Coder/decoder
system for
digital transmission.
Co-Location
Ability
of multiple
satellites to share the same approximate geostationary orbital
assignment
frequently due to the fact that different frequency bands are
used.
Color Subcarrler
A
subcarrier
that is added to the main video signal to convey the color information.
In NTSC
systems, the color subcarrier is centered on a frequency of 3.579545
MHz,
referenced to the main video carrier.
Common Carrier
Any
organization
which operates communications circuits used by other people. Common
carriers
include the telephone companies as well as the owners of the
communications
satellites, RCA, Comsat, Direct Net Telecommunications, AT&T and
others.
Common carriers are required to file fixed tariffs for specific
services.
Companding
A
noise-reduction
technique that applies single compression at the transmitter and
complementary
expansion at the receiver.
Composite Baseband
The
unclamped and unfiltered output of the satellite receiver's demodulator
circuit,
containg the video information as well as all transmitted
subcarriers.
Compression Algorithms
Software that allows
codecs to
reduce the number of bits required for data storage or
transmission.
COMSAT
The Communications Satellite
Corporation (part
of Lockheed Martin) which serves as the U.S. Signatory to INTELSAT and
INMARSAT.
Conus
Contiguous
United States.
In short, all the states in the U.S. except Hawaii and Alaska.
Cross Modulation
A
form of
signal distortion in which modulation from one or more RF carrier(s) is
imposed
on another carrier.
CSU
Channel service
unit. A
digital interface device that connects end-user equipment to the local
digital
telephone loop. CSU is frequently coupled with DSU (see below) as
CSU/DSU.
CDMA – code division multiple access - CDMA is a digital spread-spectrum modulation technique used mainly with personal communications devices such as mobile phones. CDMA digitizes the conversation and tags it with a special frequency code. The data is then scattered across the frequency band in a pseudorandom pattern. The receiving device is instructed to decipher only the data corresponding to a particular code to reconstruct the signal.
Channel Efficiency - In error correction, the ratio of the input information divided by the transmitted information plus code.
Coaxial Cable - A popular transmission medium usually consisting of one central wire conductor (two, for twin axial cable) surrounded by a dielectric insulator and encased in either a wire mesh or an extruded metal sheathing; coaxial cable comes in many varieties, depending on the degree of EMI shielding afforded and voltages and frequencies accommodated; common Community Antenna Television (Cable Antenna Television) transmission cable, typically supporting RF frequencies from 50 to about 500 MHz; also called coax.
Code Division Multiple Access - (CDMA) Method of combining multiple users on a given channel bandwidth using unique spreading codes, or hopping patterns to distinguish and given user.
Code Rate - In error correction, the ratio of information divided by information plus redundancy. Codes with a high code rate are desirable because they efficiently use the available channel for information transmission.
Codec - Semiconductor device containing both an encoder and a decoder. In communications engineering, the term codec is used in reference to integrated circuits, or chips that perform data conversion. In this context, the term is an acronym for "coder/decoder".
Coding Gain - In communications engineering, coding gain refers to the improvement in decibels (dB) that a particular code offers over other option. An improvement in coding gain can provide the designer with options such as reducing transmission power or bandwidth.
Compression Ratio - The ratio of the number of original data bytes to the number of compressed data bytes.
Compression - Any of several techniques that reduce the number of bits required to represent information in data transmission or storage (thus conserving bandwidth and/or memory), in which the original form of the information can be reconstructed; also called "compaction".
Continuous Phase Frequency Shift Keying - (CPFSK) Digital modulation format where information is conveyed in the frequency of a carrier signal ensuring that the phase is continuous between symbol transitions.
D/A Conversion - (digital-to-analog conversation) The process of converting a discrete time digital representation of a waveform to a continuous analog voltage equivalent.
D-TDMA – deterministic time division multiple access – this technology simply takes TDMA and adds the ability to prioritize types of traffic. This will allow voice and video to be prioritized above data transfers to make the best use of the bandwidth. This technology is used in digital-advanced mobile phone system (D-AMPS) and Global System for Mobile communications (GSM). Packets are transmitted based on priorities established within the router which allow for VoIP and video teleconferencing to transmit first since they are real-time traffic.
DAMA - Demand Assignment Multiple Access -- DAMA is a technique of Satellite resource manipulation that allows many users on a Satellite to share a limited assignment of transponder capacity. As one user connects to the transponder they draw from a common "pool". When that user disconnects the transponder space returns to the pool for other users to access.
DAMA, 2
A highly efficient means of instantaneously assigning telephony
channels in a transponder according to immediate traffic demands.
DBS
Direct
broadcast satellite.
Refers to service that uses satellites to broadcast multiple channels of
television programming directly to home mounted small-dish
antennas.
dBi
The dB power
relative to an
isotropic source.
dBW
The ratio of
the power to
one Watt expressed in decibels.
De-BPSK
Differential Binary Phase Shift
Keying
De-QPSK
Differential Quadrature Phase Shift
Keying.
Decibel (dB)
The
standard unit used to express the ratio of two power levels. It is used
in
communications to express either a gain or loss in power between the
input and
output devices.
Declination
The
offset angle of
an antenna from the axis of its polar mount as measured in the meridian
plane
between the equatorial plane and the antenna main beam.
Decoder
A television set-top device which enables the home subscriber to convert an electronically
scrambled television picture into a viewable signal. This should not be confused with a
digital coder/decoder known as a CODEC which is used in conjunction with digital
transmissions.
Deemphasis
Reinstatement of a
uniform baseband frequency response following demodulation.
Delay
The time it takes for a signal to go from the sending station through the satellite to the
receiving station. This transmission delay for a single hop satellite connection is very
close on one-quarter of a second.
Demodulator
A satellite receiver circuit which extracts or "demodulates" the "wanted "signals from the
received carrier.
Deviation
The
modulation level
of an FM signal determined by the amount of frequency shift from the
frequency
of the main carrier.
Digital
Conversion
of
information into bits of data for transmission through wire, fiber optic
cable,
satellite, or over air techniques. Method allows simultaneous
transmission of
voice, data or video.
Data Coding - Operating on data with an algorithm to accomplish encryption, error correction, compression, or some other feature.
dBc - The level of a signal in dB relative to a wanted carrier signal level.
dBm - The level of a signal in dB relative to 1 m W (0 dBm).
DBS, 2- Direct Broadcast Satellite is a video programming or data delivery service which is delivered via satellite directly to the end-user. An example is DircTV or Echostar.
DC - (Data Compression) A method to encode data by eliminating redundancy. May be implemented in hardware or software.
Density - A measure of how much data is stored in a given area or linear sequence (track) on a specific medium. Density may be measured in Bits per inch or millimeter, in tracks per inch or millimeter, or in bits per square inch or millimeter.
DES - (Data Encryption Standard) A Scheme approved by the National Bureau of Standards that encrypts data for security purposes. DES is the data-communications encryption standard specified by Federal Information Processing Systems (FIPS) Publication 46.
Differential Phase Shift Keying - (DPSK) Digital modulation format where information is conveyed in phase difference of a carrier signal between consecutive symbols.
Differentially Encoded Phase Shift Keying - (DEPSK) Digital modulation format where data is pre-coded to convey information in the change of state between consecutive bits, to overcome the phase ambiguity problem with coherent phase shift keying.
Digital Audio Broadcasting - (DAB) The generic name given to the new generation of radio transmission using digitally encoded audio waveforms.
DVB – Digital Video Broadcast – This is an all digital as the name indicates, and was originally designed for broadcast video and has been modified to allow various types of traffic.
DVB-S - Digital Video Broadcast via satellite
DVB-C - Digital Video Broadcast via cable
DVB-RCS – Digital Video Broadcast, Return Channel via Satellite
E1
Wide-area
digital
transmission facility used predominantly in Europe that carries data at
a rate
of 2.048 Mbit/s.
E3
Wide-area
digital
transmission facility used predominantly in Europe that carries data at
a rate
of 34.368 Mbit/s.
Earth Station
The
term used to
describe the combination or antenna, low-noise amplifier (LNA),
down-converter,
and receiver electronics. used to receive a signal transmitted by a
satellite.
Earth Station antennas vary in size from the.2 foot to 12 foot (65
centimeters
to 3.7 meters) diameter size used for TV reception to as large as 100
feet (30
meters) in diameter sometimes used for international communications. The
typical
antenna used for INTELSAT communication is today 13 to 18 meters or 40
to 60
feet.
Echo Canceller
An
electronic
circuit which attenuates or eliminates the echo effect on satellite
telephony
links. Echo cancellers are largely replacing obsolete echo
suppressors.
Echo Effect
A
time-delayed
electronic reflection of a speaker's voice. This is largely eliminated
by modern
digital echo cancellers.
Eclipse
When a satellite passes through the
line
between the earth and the sun or the earth and the
moon.
Eclipse
Protected
Refers to a transponder that can remain powered during
the
period of an eclipse.
El/Az
An antenna mount providing
independent adjustments in elevation and azimuth.
Edge of Coverage
Limit of a
satellite's
defined service area. In many cases, the EOC is defined as being 3 dB
down from
the signal level at beam center. However, reception may still be
possible beyond
the -3dB point.
EIRP - (
Effective
Isotropic
Radiated Power) - This term describes the strength of the signal leaving
the
satellite antenna or the transmitting earth station antenna, and is used
in
determining the C/N and S/N. The transmit power value in units of dBW is
expressed by the product of the transponder output power and the gain of
the
satellite transmit antenna.
Elevation
The
upward tilt to a
satellite antenna measured in degrees required to aim the antenna at the
communications satellite. When. aimed at the horizon, the elevation
angle is
zero. If it were tilted to a point directly overhead, the satellite
antenna
would have an elevation of 90 degrees.
Encoder
A device
used to
electronically alter a signal so that it can only be viewed on a
receiver
equipped with a special decoder.
Energy Dispersal
A low-frequency waveform
combined
with the baseband signal prior to modulation, to spread the FM signal's
peak
power across the available transponder bandwidth in order to reduce the
potential for creating interference to ground-based communications
services.
EOL
End of
Life of a satellite.
Equatorial Orbit
An
orbit with
a plane parallel to the earth's equator.
ESC -
(Engineering
Service Circuit)
- The 300-3,400 Hertz voice plus teletype (S+DX) channel used for earth
station-to-earth station and earth station-to-operations center
communications
for the purpose of system maintenance, coordination and general system
information dissemination. In analog (FDM/FM) systems there are two S+DX
channels available for this purpose in the 4,000-12,000 Hertz portion of
the
baseband. In digital systems there are one or two channels available
which are
usually convened to a 32 or 64 Kbps digital signal and combined with the
earth
station traffic digital bit stream. Modern ESC equipment interfaces with
any mix
of analog and digital satellite carriers, as well as backhaul
terrestrial links
to the local switching center.
Eutelsat
The European Telecommunications
Satellite
Organization which is headquartered in Paris, France. It provides a
satellite
network for Europe and parts of North Africa and the Middle Eas
Encoding/Decoding - The process of organizing information into a particular format and then reconverting it for use; for pulse-code-modulated voice transmission, the generation of digital signals to represent quantified samples, and the subsequent reverse process.
Ethernet – A popular local area network design, the product of Xerox Corp., characterized by 10 Mbps baseband transmission over a shielded coaxial cable and employing CSMA/CD as the access control mechanism; standardized by the IEEE as specification IEEE 802.3; referring to the Ethernet design or as a compatible with Ethernet.
FCC (Federal Communications
Commission) -
The U.S. federal regulatory body, consisting of five
members,
one of who is designated chairman, appointed by the President and
confirmed by
the Senate, which regulates interstate communications under the Communications
Act of 1934.
FDMA – (frequency division multiple access) – allocates a single channel to one user at a time, if the transmission path deteriorates, the controller switches the system to another channel. Although technically simple to implement, FDMA is wasteful of bandwidth and cannot handle alternate forms of a data, only voice transmissions. This is the basic technology used in cellular phones and is also used in the total access communication systems (TACS).
FEC – Forward Error Correction – It is a powerful technique for improving the performance of error-prone channels found in communication systems. It is a system of error control for data transmission where the receiving device has the capability to detect and correct any character or code block that contains fewer then a predetermined number of symbols in error. It is intended to improve the capacity of a channel by adding some carefully designed redundant information to the data being transmitted through the channel.
Feed - This term has
at least two
key meanings within the field of satellite communications. It is used to
describe the transmission of video programming from a distribution =
center. It is
also used to describe the feed system of an antenna. The feed system may =
consist
of a subreflector plus a feedhorn or a feedhorn only.
the under drops performance when lost dramatically and sudden is signal =
however,
transmission, digital a In picture. video in appear to begins sparkles
called
noise random of type threshold Below 7db. ratio carrier incoming an with pictures good provide successfully will receiver TV satellite typical
techniques, extension Using carrier. from picture television quality =
recover
detect circuitry demodulator enable enough strong just power
Fiber Optic – Transmission technology in which modulated light wave signals., generated by laser or LED, are propagated along a typically glass or plastic medium, and then demodulated to electrical signals by a light-sensitive receiver.
FTDMA – (frequency time division multiple access) – The FTDMA features a unique and patented two-dimensional satellite access scheme, which combines the TDMA slotted ALOHA and FDMA techniques. Remote terminals burst in randomly-selected frequency channels at each transmission. Occasional high traffic sites are automatically off-loaded from the shared resources and have dedicated frequency channels allotted to them upstream communications are transmitted using a patented, proprietary technology – Frequency/Time Division Multiple Access, or FTDMA. Downstream transmissions, however, use the industry standard Digital Video Broadcast (DVB) carrier.
FSK – (Frequency Shift Keying) - Digital modulation format where information is conveyed in the frequency of a carrier signal.
FTP - (File Transfer Protocol) - A very common method of moving files between two Internet sites. FTP is a special way to login to another Internet site for the purposes of retrieving and/or sending files. There are many Internet sites that have established publicly accessible repositories of material that can be obtained using FTP, by logging in using the account name anonymous, thus these sites are called anonymous ftp servers.
GMSK – (Gaussian Minimum Shift Keying) - Digital modulation format where information is conveyed in the frequency of a carrier signal, where the incoming data is first shaped with a Gaussian low-pass filter.
GSM - (Global System for Mobile Communication) - A cellular radio standard using digital GMSK modulation.
G.711 - Describes the 64-kbps PCM voice coding technique. In G.711, encoded voice is already in the correct format for digital voice delivery in the PSTN or through PBXs. Described in the ITU-T standard in its G-series recommendations.
G.723 - Audio (Voice) Compression Protocol reducing the required bandwidth per call, per direction to 8 kbps using adaptive multi-rate wideband.
G.729 - Audio (Voice) Compression Protocol reducing the required bandwidth per call, per direction to 12 kbps using conjugate-structure algebraic-code-excited linear-predication.
Geostationary Orbit – circular orbits that are orientated in the plane of the earth’s equator. The satellite appears stationary.
H.323 - is a protocol for the transmission of real-time audio, video and data information over packet switching-based networks. Such networks include IP-based (including the Internet), Internet packet exchange-based local area networks, enterprise networks and metropolitan and wide area networks. H.323 can also be applied to multipoint-multimedia communications. The technology provides a vast array of services which means it can be used in consumer, business and entertainment applications. H.323 is an essential element in ensuring that the compatibility of the mobile multimedia applications and services will be introduced with the implementation of third generation wireless technologies.
Headers - Blocks of data written at the beginning of cartridges or files that contain specific identification information.
HTPC - Hyper Turbo Product Code is a TPC with an added parity correction code dimension.
HTTP - HyperText Transfer Protocol - The protocol for moving hypertext files across the Internet. Requires a HTTP client program on one end, and an HTTP server program on the other end. HTTP is the most important protocol used in the World Wide Web.
Information Transport - Transferring electronic information or data via electronic, photonic, or any other mans. May be point to point or network, one or two way, also referred to as "communications" or "telecommunications" (same as data transport).
IP - Internet Protocol - is the most basic protocol to communicate on the Internet. An IP number is a numerical address consisting of four numbers separated by periods. Each IP address uniquely identifies a certain computer on the Internet. The domain name is used to make using them easier.
LAN - (Local Area Network) - A network of interconnected workstations sharing the resources of a single processor or server within a relatively small geographic area.
Latency - In a network, latency, a synonym for delay, is an expression of how much time it takes for a packet of data to get from one designated point to another. In some usages latency is measured by sending a packet that will be returned back to the sender and thus the round-trip time is considered the latency.
LNA – Lowe Noise Amplifier – Special type of amplifier used in communication systems to amplify very weak signals captured by an antenna.
LNB - Low Noise Block – take a block or band of relatively high frequencies and convert them to similar signals carried at much lower frequencies (intermediate frequency or IF. These lower frequencies travel through cables with much less attenuation of the signal, so there is much more signal left on the satellite receiver end of the cable. The “low noise” part means that special electronic engineering techniques are used so that the signal has less noise (unwanted signals) on the output than would be possible with less stringent engineering. If low noise engineering techniques were not used, the sound and picture of satellite would be very low quality if it could be received at all.
LNC – Low Noise Converter converters the incoming signal from the satellite (3.6 to 4.2 GHz in the c-band and 10.700 to 12.750 in ku-band) into a lower frequency (900 to 2150 MHz).
Lossless - Characteristic of data compression algorithms such that when compressed data is decompressed, it is identical to the form it had prior to compression.
Lossy - Characteristic of data compression algorithms in which compressed data may not decompress exactly to its original form. Lossy compression is typically capable of very high compression performance, and is used primarily on data which may be slightly changed without significant effect.
MCPC – Multi Channel per Carrier – This is a byproduct of SCPC combined with TDM (Time division Multiple) voice/data multiplexing that operates in a star configuration
Mesh Topology – devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network. T he topology of a network whose components are all connected directly to every other component A group of nodes sharing a large number of interconnections, where the interconnections are graphically represented with lines, can be visualized as a mesh.
Minimum Shift Keying - (MSK) - Digital modulation format where information is conveyed in the frequency of a carrier signal with modulation index equal to half the symbol period.
Modulation – the transmission of a signal by using it to vary a carrier wave, changing the carrier’s amplitude or frequency or phase. The process in which electrical encoding or modulation is used to format the information according to the transmission medium.
OC-3 - A telecommunications standard for data rate speeds of 155 Mbits/second.
ON-OFF Keying - (OOK) - Digital modulation format where information is conveyed by switching on and off a carrier signal.
Point to Multipoint - a connection consisting of a central connection endpoint and other peripheral connection endpoints and in which data originating from the central connection endpoint are received by all other connection endpoints and data originating from the peripheral connection endpoints is received only by the central connection endpoint.
Point to point – This service requires the incorporation of an earth station as the HUB with connection to needed services. It incorporates various sites with a VSAT to communicate with the HUB.
PSK - Phase-Shift Key - It's a form of phase modulation for digital signals, where the bits are quantified by various phase changes. It involves changing the phase of transmitted waveform instead of the frequency, these finite phase changes representing digital data. In its simplest form, a phase-modulated waveform can be generated by using the digital data to switch between two signals of equal frequency but opposing phase.
QoS – Quality of Service - QoS is the set of techniques to manage network resources. QoS enables you to provide better service to certain flows. This is done by either raising the priority of a flow or limiting the priority of another flow.
QPSK – Quaternary Phase-Shift Key is a more elaborate form of PSK. Each pair of bits of the incoming sequence causes a change in the carrier phase between four possible states. The carrier undergoes four changes in phase (four symbols) and can thus represent 2 binary bits of data per symbol. Although this may seem insignificant initially, a modulation scheme has now been supposed that enables a carrier to transmit 2 bits of information instead of 1, thus effectively doubling the bandwidth of the carrier.
Quadrature Amplitude Modulation - (QAM) - Digital modulation format where information is conveyed in the amplitude and phase of a carrier signal.
Redundancy - Extra bytes added to data that allows error detection and correction to occur; having backup equipment to ensure the minimal interruption.
RF - Radio Frequency
RS - Reed Solomon Codes – are block-based error correcting codes with a wide range of applications in digital communications and storage. These codes are used to correct errors in many systems including storage devices, wireless or mobile communications, satellite communications, digital television, DVB, high-speed modems such as ADSL. The Reed-Solomon encoder takes a block of digital data and adds extra “redundant” bits. Errors occur during transmission or storage for a number of reasons (for example noise or interference, scratches). The Reed-Solomon decoder processes each block and attempts to correct errors and recover the original data. The number and type of errors that can be corrected depends on the characteristics of the code.
RS-Viterbi - Reed-Solomon/Viterbi coding technology
RTP - Real-time transport protocol - The Internet-standard protocol for the transport of real-time data, including audio and video. RTP is used in virtually all voice-over-IP architectures, for videoconferencing, media-on-demand, and other applications. A thin protocol, it supports content identification, timing reconstruction, and detection of lost packets.
RX - Short for receive
SAP - This protocol is used on NetWare networks to advertise available network services. For example, a NetWare server uses SAP to let other computers know that it's offering up some shared files. This also stands for "Standard Accounting Program," a program on which some large businesses run their accounting.
SCPC – Single Channel Per Carrier
S/N ratio - Signal-to-noise ratio
SOHO – Small Office, Home Office
SSL - Secured Sockets Layer - a protocol that transmits your communications over the Internet in an encrypted form. SSL ensures that the information is sent, unchanged, only to the server you intended to send it to. Online shopping sites frequently use SSL technology to safeguard your credit card information.
Star Topology - Network designed in the shape of a star, where all end points are connected to one central switching device, or hub. Star networks are easier to manage than ring topology but are slower because every message must pass through the central point.
SER - (Symbol Error Rate) - The probability of receiving a symbol in error (not to be confused with BER)
Symmetrical - or full duplex is for two way communications such as voice or any real time data.
TCC - Turbo Convolutional Codes
TPC - Turbo Product Codes – These codes have performance approaching the theoretical limit for any error correction code. TPC uses block codes solving multiple steps simultaneously, thereby achieving high data throughput in hardware. They do not suffer from the error floor at low BERs that have been attributed to other codes.
TCP/IP – Transmission Control Protocol/Internet Protocol - the suite of communications protocols used to connect hosts on the Internet. TCP/IP uses several protocols, the two main ones being TCP and IPP. TCP/IP is built into the UNIX operating system and is used by the Internet, making it the de facto standard for transmitting data over networks. Even network operating systems that have their own protocols, such as Netware, also support TCP/IP
TDMA – time division multiple access – is digital transmission technology that allows a number of users to access a single radio-frequency (RF) channel without interference by allocating unique time slots to each user within each channel. Each caller is assigned a specific time slot for transmission.
TX - Short for Transmit
UNIX® - Operating system originally designed by AT&T for communicating multi-user, 32-bt minicomputers; has come into wide commercial acceptance because of its predominance in academia and its programming versatility. AT&T System V Version 3 and Berkeley System Development Version 4.3 are currently popular.
VAN - (Value Added Network) - A network whose services go beyond simple switching.
Viterbi Encoding/Decoding – is widely used for satellite and other noisy communication channels. There are two important components of a channel using Viterbi encoding: the Viterbi encoder (at the transmitter) and Viterbi Decoder (at the receiver). A Viterbi encoder includes extra information in the transmitted signal to reduce the probability of errors in the received signal that may be corrupted by noise.
V.35
ITU-T standard
describing
a synchronous, physical layer protocol used for communications between a
network
access device and a packet network. V.35 is most commonly used in the
United
States and in Europe, and is recommended for speeds up to 48
Kbit/s.
Van Allen radiation belts
These are two high
level
radiation belts discovered by an Explorer Satellite designed by Dr. Van
Allen of
Cal Tech. These belts which are highly destructive to communications
satellites
consists of two belts of highly charged particles and high energy
neutrons.
VBI
Vertical blanking
interval.
Vertical
Interval Test Signal
A method whereby broadcasters add test
signals to
the blanked portion of the vertical interval. Normally placed on lines
17
through 21 in both field one and two.
Very High Frequencies
(VHF)
The range of frequencies extending from 30 to 300 MHz; also
television channels 2 through 13.
VSAT
Very small aperture terminal. Refers to small earth
stations,
usually in the 1.2 to 2.4 meter range. Small aperture terminals under
0.5 meters
are sometimes referred to Ultra Small Aperture Terminals (USAT's)
VSWR
Voltage Standing Wave Ratio. A measurement of
mismatch in a
cable, waveguide, or antenna system.
VoIP - Voice over Internet Protocol - A technology for transmitting voice, such as ordinary telephone calls, over packet-switched data networks. Also called IP telephony.
VPN - Virtual Private Network - Network scheme in which portions of a network are connected via Internet, but information sent across the Internet is encrypted. The result is a "virtual network" which is also part of a larger network entity. This allows users to privately share private information over a public infrastructure. VPNs are often used to connect offices.
VSAT – Very Small Aperture Terminal to receive/transmit terminals installed at dispersed sites connected to a central hub via satellite using small diameter antenna dishes (0.6 to 3.8 meters).
Wideband - A system in which multiple channels access a medium (usually coaxial cable) that has a large bandwidth, greater than that of a voice-grade channel; typically offers higher-speed data-transmission capability. Also see broadband.
X-Band
The frequency band in the 7-8 GHz
region which
is used for military satellite communications
X.25
A
set of
packet switching standards published by the
CCITT.
X.400
A set
of CCITT standards for global messaging.
Zulu Time
This is the same a Greenwich
Meridian Time
(GMT). This is the time standard used in global satellite systems such
as
INTELSAT and INMARSAT in order to achieve global synchronization
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