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Корпоративные сети спутниковой связи на базе технологии VSAT

VSAT для речных и морских судов

Спутниковая связь для ТЭК

Термины

Amplifier: - A device used to boost the strength of an electronic signal.
Analog: - A form of transmitting information characterized by continuously variable quantities, as opposed to digital transmission, which is characterized by discrete bits of information in numerical steps. An analog signal is responsive to changes in light, sound, heat and pressure.
Analog-to-Digital Conversion (ADC): - Process of converting analog signals to a digital representation. DAC represents the reverse translation.
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.
Attenuation: - The loss in power of electromagnetic signals between transmission and reception points.
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.
Backoff: - The process of reducing the input and output power levels of a traveling wave tube to obtain more linear operation.
Bandwidth: - 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.
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.
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.
Business Television: - Corporate communications tool involving video transmissions of information via satellite. Common uses of business television are for meetings, product introductions and training.
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 downlink frequencies in tandem with the 5.925 to 6,425 GHz band that serves as the uplink.
C/No: - Carrier-to-noise ratio measured either at the Radio Frequency (RF) or Intermediate Frequency (IF)
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 signals the higher the C/N, the better the received picture.
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.
DAMA: - Demand-Assigned Multiple Access - A highly efficient means of instantaneously assigning telephony channels in a transponder according to immediate traffic demands.
DBW: - The ratio of the power to one Watt expressed in decibels.
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.
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.
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.
Digital Speech Interpolation: - DSI - A means of transmitting telephony. Two and One half to three times more efficiently based on the principle that people are talking only about 40% of the time.
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 65 centimeters to 3.7 meters diameter size used for TV reception to as large as 30 meters in diameter sometimes used for international communications. The typical antenna used for INTELSAT communication is today 13 to 18 meters.
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.
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.
F/D: - Ratio of antenna focal length to antenna diameter. A higher ratio means a shallower dish.
FDMA: - Frequency division multiple access. Refers to the use of multiple carriers within the same transponder where each uplink has been assigned frequency slot and bandwidth. This is usually employed in conjunction with Frequency Modulation.
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.
Feedhorn: - A satellite TV receiving antenna component that collects the signal reflected from the main surface reflector and channels this signal into the low-noise amplifier (LNA)
FM: - Frequency Modulation - A modulation method whereby the baseband signal varies the frequency of the carrier wave.
Footprint: - A map of the signal strength showing the EIRP contours of equal signal strengths as they cover the earth's surface. Different satellite transponders on the same satellite will often have different footprints of the signal strength. The accuracy of EIRP footprints or contour data can improve with the operational age of the satellite. The actual EIRP levels of the satellite, however, tends to decrease slowly as the spacecraft ages.
Forward Error Correction (FEC): - Adds unique codes to the digital signal at the source so errors can be detected and corrected at the receiver.
Frequency: - The number of times that an alternating current goes through its complete cycle in one second of time. One cycle per second is also referred to as one hertz; 1000 cycles per second, one kilohertz; 1,000,000 cycles per second, one megahertz: and 1,000,000,000 cycles per second, one gigahertz.
Frequency Coordination: - A process to eliminate frequency interference between different satellite systems or between terrestrial microwave systems and satellites. In the U.S. this activity relies upon a computerized service utilizing an extensive database to analyze potential microwave interference problems that arise between organizations using the same microwave band. As the same C-band frequency spectrum is used by telephone networks and CATV companies when they are contemplating the installation of an earth station, they will often obtain a frequency coordination study to determine if any problems will exist.
G/T: - A figure of merit of an antenna and low noise amplifier combination expressed in dB. "G" is the net gain of the system and "T" is the noise temperature of the system. The higher the number, the better the system.
Gain: - A measure of amplification expressed in dB.
Geostationary: - Refers to a geosynchronous satellite angle with zero inclination. so the satellite appears to hover over one spot on the earth's equator.
Geosynchronous: - The Clarke circular orbit above the equator. For a planet the size and mass of the earth, this point is 22,237 miles above the surface.
Gigahertz (GHz): - One billion cycles per second. Signals operating above 3 Gigahertz are known as microwaves. above 30 GHz they are know as millimeter waves. As one moves above the millimeter waves signals begin to take on the characteristics of Iightwaves.
Global Beam: - An antenna down-link pattern used by the Intelsat satellites, which effectively covers one-third of the globe. Global beams are aimed at the center of the Atlantic, Pacific and Indian Oceans by the respective Intelsat satellites, enabling all nations on each side of the ocean to receive the signal. Because they transmit to such a wide area, global beam transponders have significantly lower EIRP outputs at the surface of the Earth as compared to a US domestic satellite system which covers just the continental United States. Therefore, earth stations receiving global beam signals need antennas much larger in size (typically 10 meters and above (i.e.30 feet and up). Gregorian Dual-reflector antenna system employing a paraboloidal main reflector and a concave ellipsoidal subreflector.
Hertz (Hz): - The name given to the basic measure of radio frequency characteristics. An electromagnetic wave completes a full oscillation from its positive to its negative pole and back again in what is known as a cycle. A single Hertz is thus equal to one cycle per second.
Hub: - The master station through which all communications to, from and between micro terminals must flow. in the future satellites with on-board processing will allow hubs to be eliminated as MESH networks are able to connect all points in a network together.
IBS: - INTELSAT Business Services.
INTELSAT: - The International Telecommunications Satellite Organization operates a network of satellites for international transmissions.
ISDN - Integrated Services Digital Network.: - A CCITT standard for integrated transmission of voice, video and data. Bandwidths include: Basic Rate Interface - BR (144 Kbps - 2 B & 1 D channel) and Primary Rate - PRI (1.544 and 2.048 Mbps).
ITU: - International Telecommunication Union.
Kbps: - Kilobits per second. Refers to transmission speed of 1,000 bits per second.
Kelvin (K): - The temperature measurement scale used in the scientific community. Zero K represents absolute zero, and corresponds to minus 459 degrees Fahrenheit or minus 273 Celsius. Thermal noise characteristics of LNA are measured in Kelvins.
Kilohertz (kHz): - Refers to a unit of frequency equal to 1,000 Hertz.
Ku Band: - The frequency range from 10.9 to 17 GHz.
L-Band: - The frequency range from 0.5 to 1.5 GHz. Also used to refer to the 950 to 1450MHz used for mobile communications.
Leased Line: - A dedicated circuit typically supplied by the telephone company.
Low Noise Amplifier (LNA): - This is the preamplifier between the antenna and the earth station receiver. For maximum effectiveness, it must be located as near the antenna as possible, and is usually attached directly to the antenna receive port. The LNA is especially designed to contribute the least amount of thermal noise to the received signal.
Low Noise Block Downconverter (LNB): - A combination Low Noise Amplifier and downconverter built into one device attached to the feed.
Megahertz (MHz): - Refers to a frequency equal to one million Hertz, or cycles per second.
Modulation: - The process of manipulating the frequency or amplitude of a carrier in relation to an incoming video, voice or data signal.
Modulator: - A device which modulates a carrier. Modulators are found as components in broadcasting transmitters and in satellite transponders. Modulators are also used by CATV companies to place a baseband video television signal onto a desired VHF or UHF channel. Home video tape recorders also have built-in modulators which enable the recorded video information to be played back using a television receiver tuned to VHF channel 3 or 4.
Multiplexing: - Techniques that allow a number of simultaneous transmissions over a single circuit.
Noise: - Any unwanted and unmodulated energy that is always present to some extent within any signal.
Packet Switching: - Data transmission method that divides messages into standard-sized packets for greater efficiency of routing and transport through a network.
Parabolic Antenna: - The most frequently found satellite TV antenna, it takes its name from the shape of the dish described mathematically as a parabola. The function of the parabolic shape is to focus the weak microwave signal hitting the surface of the dish into a single focal point in front of the dish. It is at this point that the feedhorn is usually located.
Polarization: - A technique used by the satellite designer to increase the capacity of the satellite transmission channels by reusing the satellite transponder frequencies. In linear cross polarization schemes, half of the transponders beam their signals to earth in a vertically polarized mode; the other half horizontally polarize their down links. Although the two sets of frequencies overlap, they are 90 degree out of phase, and will not interfere with each other. To successfully receive and decode these signals on earth, the earth station must be outfitted with a properly polarized feedhorn to select the vertically or horizontally polarized signals as desired.
QPSK - Quadrature Phase Shift Keying: - System of modulating a satellite signal.
Receiver (Rx): - An electronic device which enables a particular satellite signal to be separated from all others being received by an earth station, and converts the signal format into a format for video, voice or data.
Satellite: - A sophisticated electronic communications relay station orbiting 22,237 miles above the equator moving in a fixed orbit at the same speed and direction of the earth (about 7,000 mph east to west).
Signal to Noise Ratio (S/N): - The ratio of the signal power and noise power. A video S/N of 54 to 56 dB is considered to be an excellent S/N, that is, of broadcast quality. A video S/N of 48 to 52 dB is considered to be a good S/N at the headend for Cable TV.
Single-Channel-Per-Carrier (SCPC): - A method used to transmit a large number of signals over a single satellite transponder.
Splitter: - A passive device (one with no active electronic components) which distributes a television signal carried on a cable in two or more paths and sends it to a number of receivers simultaneously.
Synchronization (Sync): - The process of orienting the transmitter and receiver circuits in the proper manner in order that they can be synchronized.
T1: - The transmission bit rate of 1.544 millions bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second.
TDMA: - Time division multiple access. Refers to a form of multiple access where a single carrier is the shared by many users. Signals from earth stations reaching the satellite consecutively are processed in time segments without overlapping.
Transmitter: - An electronic device consisting of oscillator, modulator and other circuits which produce a radio or television electromagnetic wave signal for radiation into the atmosphere by an antenna.
Transponder: - A combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Transponders have a typical output of five to ten watts, operate over a frequency band with a 36 to 72 megahertz bandwidth in the L, C, Ku, and sometimes Ka Bands or in effect typically in the microwave spectrum, except for mobile satellite communications. Communications satellites typically have between 12 and 24 onboard transponders although the INTELSAT VI at the extreme end has 50.
Uplink: - The earth station used to transmit signals to a satellite
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)
X.25: - A set of packet switching standards published by the CCITT.

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