Communication
Communication
transmission and reception of messages (information) using technical means... Includes transmitting devices, networks of nodes and channels (lines) of communication. Depending on the nature of the means used, it is divided into wired (messages are transmitted over copper, fiber-optic or coaxial cables), wireless (transmitted by radio signals, microwave radio signals via satellite systems) and mixed... One of the types of communication is also traditional mail, which delivers from one place to another not only written messages (letters), but also money orders, parcels, parcels, periodicals. Wired types of communication: telegraph (invented in 1844), telephone (1876) and its varieties (teletype, telefax); wireless: radio (1895), television (1923), cellular communications (mobile radiotelephones), satellite communications systems, global navigation systems; mixed view: computer networks (Internet and e-mail), information on which is transmitted both by wire (via telephone and direct lines) and out-of-wire (via satellite communication systems and cell phones). Main communication performance is the number of telephone lines, Internet service providers, radio and television broadcasting stations; the number of Internet users, mobile cellular (or simple) telephones, televisions and radios per 1000 inhabitants.
The largest number of telephone lines (million, in the country as a whole) in 2004 had the USA (268), China (312), India (67), Japan (59), Germany (55), Brazil (42), Russia ( 40); number of cell phones (million) - USA (195), China (335), Japan (92), Russia (74), Germany (71), Brazil (66), Italy (63); number of Internet users (million) - USA (204), Japan (86), China (111), India (51), Germany (49), UK (38), South Korea (34) Italy (29); the number of TVs (million) - in China (400), USA (219), Japan (87), India (63), Russia (61), Germany (51), Brazil (37), France (35). In 2000, Russia had 35 Internet providers, 9.2 million Internet users, 7,085 television stations, 2.5 million cell phones, 30.2 million Internet users. regular phones (206 devices per 1,000 inhabitants; in the USA - 661), 40.8 thousand post offices (sent 1.1 billion letters, 13.5 million parcels, 425 million money transfers, including pensions).
Geography. A modern illustrated encyclopedia. - M .: Rosman. Edited by prof. A.P. Gorkina. 2006 .
Synonyms:
See what "connection" is in other dictionaries:
connection - communication, and ... Russian spelling dictionary
COMMUNICATION, connection, about connection, in connection and (with someone to be) in connection, wives. 1. That which connects, connects something with something; a relationship that creates something in common between something, mutual dependence, conditioning. “... The connection between science and ... ... Dictionary Ushakova
And, offer. about communication, communication and communication; g. 1. The relationship of mutual dependence, conditioning. Direct, indirect, logical, organic, causal p. C. facts, phenomena, events. C. between industry and agriculture... S. science and ... ... encyclopedic Dictionary
Communication is the relationship of generality, connection, or consistency. Communication the ability to transmit information at a distance (including: radio relay communication, cellular communication, satellite communication and other types). The chemical bond is the connection of atoms ... Wikipedia
Clutch, connecting link. Concatenation of thoughts, concepts, association of ideas. See union .. influential connection ... Dictionary of Russian synonyms and expressions similar in meaning. under. ed. N. Abramova, M .: Russian dictionaries, 1999. connection logic, coherence, ... ... Synonym dictionary
Noun, f., Uptr. often Morphology: (no) what? communication, why? communication, (see) what? communication, what? communication, about what? about communication; pl. what? communication, (no) what? connections, what? connections, (see) what? communication, what? connections, about what? about connections 1. A relationship is a relationship ... ... Dmitriev's Explanatory Dictionary
In philosophy, the interdependence of the existence of phenomena separated in space and time. connections are classified according to the objects of cognition, according to the forms of determinism (unambiguous, probabilistic and correlation), according to their strength (rigid and ... ... Big Encyclopedic Dictionary
In psychology, the fact that irritations perceived by the senses form the basis of perceptions, in which there is a connection between the parts of the perceived, due to which a kind of integral formation is obtained, and not separate perceptions, ... ... Philosophical Encyclopedia
In entity relationship diagrams, the identifier of the requirements according to which the entity is involved in the relationship. Each relationship connects an entity and a relationship and can only be directed from relationship to entity. See also: Entity Diagrams ... ... Financial vocabulary
Transmission and reception of information using various technical means. Since ancient times, people needed to communicate, and the exchange of information has always been inherent in them, over time, only the methods of storing and transmitting information have improved. Communication first ... ... Encyclopedia of technology
COMMUNICATION - (1) information transmission and reception of messages using various technical means (radio, email, telephone, telegraph, teletype, television, radio relay facilities, etc.). Informational S. can be local, distant, ground, ... ... Big Polytechnic Encyclopedia
Books
- The connection of planets, times and generations, Mikhailova Lyubov Vasilievna. The connection of planets, times and generations constantly worries humanity. I feel an inextricable connection with space and try to unravel at least some of the mysteries of the universe. Earthly and unearthly love ...
The technical means used to deliver information include a variety of communications. They involve the use of facsimile, telephone, computers equipped with modems, etc. All these devices make it possible to organize various types of communication. The user does not know the methods used to implement the session.
Traditional types of communication are divided into:
Postal (carrying graphic and alphanumeric information);
Telephone (transmitting speech);
Telegraphic (designed to carry alphanumeric messages);
Facsimile (facilitating the transmission of graphic and alphanumeric information);
Radio relay and satellite communications.
In this case, they can be wired (telegraph, telephone, etc.), as well as wireless. In the second type of communication, in turn, separate groups are classified (radio, radio relay, and At the same time, speech transmission, for example, is possible by means of almost any of the types.
Modern types of communication are divided into:
Telephone;
Computer telephony;
Radiotelephone;
Radiotelephone cellular communication systems;
Systems included in the Wi-Fi standard.
This type of communication, as telephone, is the most widely used and widespread. It is used not only for contacts between people, but also for more enterprises, the administrative body, as well as for the implementation of financial and economic activities. Depending on the type of telephone use, communication is divided into two main types:
For common use (international, intercity and city);
Internal, applied within only one organization.
In the technology of computer telephony, the main role is assigned. The use of this type of communication contributes to a significant acceleration of the process of operational management of the enterprise, while increasing the quality and efficiency of administration with a minimum amount of costs. Application of modern computer technology allows you to reduce the amount to pay for long-distance and international calls.
Such types of communication as radiotelephone are used in the process of transferring information wireless systems... This allows you to significantly reduce the costs incurred for the installation of expensive communications and their subsequent maintenance. This type of communication is very mobile and can be quickly organized in any area. Currently, radiotelephony is an excellent alternative to wireline telephony.
The reason for the emergence of cellular communications is the emerging need to create an extensive network of radiotelephone mobile communications. Currently, this method of transferring information is used in more than one hundred and forty countries on all continents.
Towards modern wireless technologies Wi-Fi also applies. The principle of information transfer with this type of communication is based on the connection of a number of computers in the network or their connection to the Internet.
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The telegraph is, the definition
The telegraph is a means of transmitting a signal through wires or other telecommunication channels.
The telegraph is a system of technical devices for transmitting messages over a distance over wires using.
The telegraph is a means of transmitting signals through wires, radio or other communication channels.
The telegraph is a device for transmitting any signals (for example letters) over a distance using electricity through wires.
The telegraph is an institution, a building in which notifications sent in this way are accepted for sending and received.
The telegraph is a communication system that provides fast transfer messages at a distance - by means of electrical signals via wires or by radio - with their recording at the receiving point.
Bodo apparatus - a new stage in the development of telegraphy
In 1872, the French inventor Jean Baudot designed a reusable telegraph apparatus that could transmit two or more messages in one direction over one wire. The Bodo apparatus and those created according to its principle were called start-stop. In addition, Bodo created a very successful telegraph code (Bodo Code), which was subsequently adopted everywhere and received the name International Telegraph Code No. 1 (ITA1). The modified version of MTK No. 1 was named MTK No. 2 (ITA2). In the USSR, the telegraph code MTK-2 was developed on the basis of ITA2. Further modifications to the design of the start-stop telegraph apparatus proposed by Baudot led to the creation of teleprinters (teletypes). In honor of Bodo, the unit of information transmission speed was named - baud.
Telex
By 1930, the design of a start-stop telegraph apparatus was created, equipped with a disk-type telephone dialer (teletype). This type of telegraph apparatus, among other things, made it possible to personify the subscribers of the telegraph network and make them quickly connect. Almost at the same time, national subscriber telegraph networks were created in the UK, called Telex (Telegraph + EXchange).
Sources and links
Sources of text, images and videos
ru.wikipedia.org
scsiexplorer.com.ua
Possibilities of various types of communication in emergency situations.
Wired telephone (fixed) communication, local telephone communication is a telephone connection between users telephone connectionthrough wired connections. Public telephone network, PSTN is a subscriber communications network, for access to which telephones, automatic telephone exchanges and data transmission equipment are used. The provision of end-user access to the public telephone network is the responsibility of the telephone operators. In the overwhelming majority of cases, each PSTN subscriber receives a certain unique (globally or within a specific network segment) identifier - phone number... By the type of connection, it is significantly inferior to cellular communication. IN this moment all virtues are supplanted by other types of communication. Disadvantages: wire breaks on the line, attachment to a specific place, high cost for long-distance calls.
Cellular (mobile) communication is a type of telecommunications, in which graphic and voice information is transmitted to wireless terminals that are not tied to any particular place or territory; it is a convenient means of communication. By exchanging packets between cell phone and the base station is in constant contact. The reliability of communication depends on many factors: 1) this is the coverage area, it is worth failing one or two "cells - base stations", Problems will begin. 2) cellular communication is subject to eavesdropping by others (third parties).
Satellite connection - one of the types of space radio communication based on the use artificial satellites land as repeaters located at very high altitudes (from tens to hundreds of thousands of kilometers). Satellite communication is carried out between earth stations, which can be both fixed and mobile. To organize communication, one satellite is enough - a repeater, which has an orbit at a very high altitude. Failure of one of the system elements leads to a disconnection.
Finding the geostationary orbit of the relay satellite is also of great importance. Basically, these orbits are closer to the equator, and therefore in our northern regions, satellite communications have problems. Moreover, in the initial period of hostilities, many satellites will be destroyed.
VHF radio communication is organized in the radio wave range with a frequency from 30 MHz to 3000 MHz, and practically within the line of sight. VHF radio waves are not reflected from the ionosphere, but go into outer space. In a flat area of \u200b\u200bterrain (for example, a sea surface), the communication range is possible up to 11 km, when the antenna is raised relative to the surface, the range increases. Using good VHF equipment, good antennas, it is possible to increase the communication range to 40-50 km. Negative factors are: rugged terrain, tall buildings, which are an obstacle to the propagation of VHF radio waves, which reduces the communication range.
VHF band advantages:
- Low level of external interference.
- The ability to accommodate a large number of communication channels without mutual interference.
- The higher the carrier frequency, the more information can be transmitted on it.
- The propagation distance depends little on meteorological conditions.
- Receiving and transmitting antennas are small.
- High quality of transmitted audio information.
- Limited communication range.
- Wave diffraction affects transmission conditions in an obstacle area, resulting in poor reception areas (or dead zones).
Shortwave radio communication - organized in the radio wave range, with a frequency from 3 MHz to 30 MHz, also has its advantages and disadvantages.
Advantages - having a certain set of frequencies, you can conduct radio communications almost around the clock.
Disadvantages - all classic antennas (rod, dipole, triangle) have a certain angle of radiation relative to the ground, therefore, "dead zones" appear, i.e. the signal emitted by the antenna is reflected from the ionosphere and is received by the correspondent only at a certain distance, which depends on the frequencies used, the type of antenna, the season and time of day. The higher the used frequency, the larger the "dead zone". Below is a drawing of the structure of the ionosphere. The lowest layer of the ionosphere, D, located above the Earth at an altitude of 60 to 90 km. It is formed only during the daytime, when the intensity of solar ionizing radiation is high, and disappears at night. Layer D plays an essential role in the organization of communication at frequencies of 3-8 MHz - this is the concept of "day" and "night" transmission. Using classical antennas in the daytime, it is possible to establish radio communications with a surface wave (40-60 km) and unstable radio communications with a reflected wave (layer D partially or completely absorbs signals from radio stations - the effect of signal fading, the station disappears and appears).
The structure of the ionosphere.
The atmosphere is called the gaseous envelope of the earth. The earth's atmosphere, made up of air and moisture, is the main medium where radio waves propagate. The composition of the atmosphere is not uniform.
Atmosphere in three parts:
- the upper layer of the atmosphere at altitudes above 60 km is called the ionosphere.
- the layer of the atmosphere at altitudes of 20-60 km is called the stratosphere.
- the lower part of the atmosphere up to heights of 10 - 20 km is called the troposphere.
Radiation angles of HF antennas.
Radiation angles of the "Shtyr" antenna.
Radiation angles of the Dipole antenna.
Currently, an individual entrepreneur Pavel Arkadievich Vladimirov has the opportunity to provide radio communication on HF without "dead zones", i.e. from 0 to 400-600 km, which was preceded by development and long-term testing small-sized HF antennas in various regions and climatic regions of our country.
As a result, developed and put into production in 2013 small-sized short-wave antenna-feeder devices of the "MRV" serieswho are not inferior in their technical specifications models of well-known world manufacturers, and in some matters even surpass them.
For instance:
1) collapsible design of the emitter, which provides convenience during transportation.
2) the emitter is made of AD31 aluminum (used in aviation and mechanical engineering), which increases the service life and allows the use of the AFU in different climatic zones and at different times of the year.
3) the directional pattern is circular, there is a small minimum, but it is felt only in the near zone - the wavelength (Lambda - in the figures this minimum is highlighted in red). Signal emission corresponds AZI (anti-aircraft radiation antenna), but only in low-frequency parts of the HF range (2.3 MHz, sometimes 4 MHz, depending on the season and time of day).
4) low suspension height (2m mast included), and small installation area. "MRV" diagram.
This is the performance characteristics of "MRV":
And they will be like this:
"MRV-4" - range: 1.875 - 7.3 MHz; emitter diameter: 4 m; VSWR: no more than 1.2; input power: up to 150 watts; impedance: 50 ohms.
AFU composition:
1) the antenna itself;
5) control cable - 28 m;
6) control panel - 1 pc.
"MRV-3.2" - range: 2.3 - 8.5 MHz; emitter diameter: 3.2 m; VSWR: no more than 1.2; input power: up to 150 watts; impedance: 50 ohms.
AFU composition:
1) the antenna itself;
2) fiberglass mast 2 meters high - 1 pc .;
3) two tiers of guys, 1st - 4 pieces, 10 m each, 2nd - 4 pieces, 5 m each;
4) coaxial cable with connectors - 28 m;
5) control cable - 28 m;
6) control panel - 1 pc.
7) power meter and VSWR with a cable for connection to a radio station.
"MRV-1.9" - range: 3.5 - 12.5 MHz; emitter diameter: 1.9 m; VSWR: no more than 1.2; input power: up to 150 watts; impedance: 50 ohms.
AFU composition:
1) the antenna itself;
2) fiberglass mast 2 meters high - 1 pc .;
4) coaxial cable with connectors - 28 m;
5) control cable - 28 m;
6) control panel - 1 pc.
7) power meter and VSWR with a cable for connection to a radio station.
"MRV-1" - range: 14.0 - 29.9 MHz; emitter diameter: 1.0 m; VSWR: no more than 1.2; input power: up to 150 watts; impedance: 50 ohms. (In Tver - the Ministry of Emergency Situations is used at the truckers' frequency - 27.135 MHz).
AFU composition:
1) the antenna itself;
2) fiberglass mast 2 meters high - 1 pc .;
3) one tier of guy wires - 4 pieces, 5 m each;
4) coaxial cable with connectors - 28 m;
5) control cable - 28 m;
6) control panel - 1 pc.
7) power meter and VSWR with a cable for connection to a radio station.
Satellite communication is one of the types of radio communication based on the use of artificial earth satellites as repeaters. Satellite communication is carried out between earth stations, which can be both fixed and mobile. Satellite communication is a development of traditional radio relay communication by placing a repeater at a very high altitude (from hundreds to tens of thousands of kilometers). Since the zone of its visibility in this case is almost half of the Earth, the need for a chain of repeaters disappears in most cases, and one is enough.
In 1945, in the article "Extraterrestrial Relays", published in the October issue of the magazine "Wireless World", the English scientist, writer and inventor Arthur Clarke proposed the idea of \u200b\u200bcreating a system of communication satellites in geostationary orbits that would allow organizing global communication system. Subsequently, Clarke, when asked why he did not patent the invention (which was quite possible), replied that he did not believe in the possibility of implementing such a system during his lifetime, and also believed that such an idea should benefit all of humanity. The first studies in the field of civil satellite communications in Western countries began to appear in the second half of the 50s of the XX century. In the United States, they were prompted by the increased need for transatlantic telephone communications.
On August 20, 1964, 11 countries (the USSR was not included in their number) signed an agreement on the creation of the International Telecommunications Satellite organization (Intelsat). By that time, the USSR had its own developed satellite communications program, crowned on April 23, 1965 with the successful launch of the communication Soviet satellite Molniya-1. Under the Intelsat program, the first commercial communications satellite, Early Bird (COMSAT Corporation) was launched on April 6, 1965. By today's standards, the Early Bird satellite (INTELSAT I) had more than modest capabilities: 50 MHz, it could provide up to 240 telephone communication channels.At any given time, communication could be carried out between an earth station in the United States and only one of three earth stations in Europe (in the UK, France or Germany), which were interconnected by cable lines communication.
Later, the technology made a step forward, and the INTELSAT IX satellite already had a bandwidth of 3456 MHz. For a long time in the USSR, satellite communications were developed only in the interests of the USSR Ministry of Defense. Due to the greater secrecy of the space program, the development of satellite communications in the socialist countries proceeded differently than in the Western countries. The development of civil satellite communications began with an agreement between 9 countries of the socialist bloc on the creation of the Intersputnik communications system, which was signed only in 1971.
In the early years of research, passive satellite repeaters were used (examples are the Echo and Echo-2 satellites), which were a simple radio signal reflector (often a metal or polymer sphere with metal sputtering) that did not carry any transmitting equipment on board. Such satellites have not become widespread. All modern communication satellites are active. Active repeaters are equipped with electronic equipment for signal reception, processing, amplification and retransmission.
Satellite repeaters can be non-regenerative and regenerative. A non-regenerative satellite, having received a signal from one earth station, transfers it to another frequency, amplifies and transmits it to another earth station. The satellite can use several independent channels carrying out these operations, each of which works with a certain part of the spectrum (these processing channels are called transponders). The regenerative satellite demodulates the received signal and re-modulates it. As a result, error correction is performed twice: at the satellite and at the receiving earth station. The disadvantages of this method are the complexity (and hence the much higher cost of the satellite), as well as the increased signal transmission delay.
An important type of equatorial orbit is the geostationary orbit, the geostationary orbit in which the satellite rotates at an angular velocity equal to the Earth's angular velocity in the direction coinciding with the direction of the Earth's rotation. constantly.
However, there is only one geostationary orbit, and it is impossible to launch all satellites into it. Its other disadvantage is its high altitude, and hence the high cost of launching a satellite into orbit. In addition, a satellite in geostationary orbit is unable to serve earth stations in the circumpolar region. An inclined orbit can solve these problems, however, due to the movement of the satellite relative to the ground observer, it is necessary to launch at least three satellites into one orbit in order to provide round-the-clock access to communications. Polar orbit is the extreme case of inclined (inclined 90º) inclination When inclined orbits are used, earth stations are equipped with tracking systems that direct the antenna to the satellite. Stations operating with satellites in geostationary orbit are usually also equipped with such systems to compensate for deviations from the ideal geostationary orbit. An exception is small antennas used to receive satellite television: their radiation pattern is wide enough, so they do not feel satellite vibrations near the ideal point. Frequency reuse of coverage area.
Since radio frequencies are limited resource, it is necessary to ensure that the same frequencies can be used by different earth stations. This can be done in two ways: spatial separation, each satellite antenna receives a signal only from a certain region, while different regions can use the same frequencies, polarization separation, different antennas receive and transmit a signal in mutually perpendicular polarization planes, while the same frequencies can be applied two times (for each of the planes). polarization
A typical coverage map for a satellite in geostationary orbit includes the following components: the global beam communicates with earth stations throughout the coverage area, and is assigned frequencies that do not intersect with other beams on that satellite. rays of the western and eastern hemispheres, these rays are polarized in the plane A, and the same frequency range is used in the western and eastern hemispheres. the zone beams are polarized in the B plane (perpendicular to A) and use the same frequencies as the hemisphere beams. Thus, an earth station located in one of the zones can also use hemispherical beams and a global beam. In this case, all frequencies (except for those reserved for the global beam) are used repeatedly: in the western and eastern hemispheres and in each of the zones.
The choice of frequency for data transmission from earth station to satellite and from satellite to earth station is not arbitrary. The frequency depends, for example, the absorption of radio waves in the atmosphere, as well as the required dimensions of the transmitting and receiving antennas. Radio waves in the atmosphere Frequencies used in satellite communications are divided into ranges designated by letters.
Application L, 1.5 GHz, Mobile satellite communications. S, 2.5 GHz, Mobile satellite C, 4 GHz, 6 GHz, Fixed satellite X, Frequencies are not defined for satellite communications by ITU-R recommendations. For radar applications, the specified range is 8-12 GHz. Fixed satellite (military) Ku, 11 GHz, 12 GHz, 14 GHz, Fixed satellite, K satellite, 20 GHz, Fixed satellite, Ka satellite, 30 GHz, Fixed satellite, intersatellite
A feature of satellite communication systems is the need to operate in conditions of a relatively low signal-to-noise ratio caused by several factors: the signal-to-noise ratio, a significant distance between the receiver and the transmitter, limited satellite power (inability to transmit at high power). In this regard, satellite communications are poorly suited for transmission analog signals... Therefore, to transmit speech, it is pre-digitized using (PCM). Analog signals are digitized To transmit digital data via a satellite communication channel, they must first be converted into a radio signal occupying a certain frequency range. For this, modulation is applied (digital modulation is also called keying). The most common types of digital modulation for satellite communications applications are phase shift keying and quadrature amplitude modulation. For example, DVB-S2 systems use QPSK, 8-PSK, 16-APSK, and 32-APSK. DVB-S2 Phase Shift Keying Modulation
Modulation is performed at the earth station. The modulated signal is amplified, transferred to the desired frequency and fed to the transmitting antenna. The satellite receives a signal, amplifies, sometimes regenerates, transmits to another frequency and, using a certain transmitting antenna, broadcasts to the ground. Antenna regenerates Due to the low signal power, there is a need for error correction systems. For this, various error-correcting coding schemes are used, most often various versions of convolutional codes (sometimes in combination with Reed-Solomon codes. Noise-correcting coding of convolutional codes with Reed-Solomon codes
VSAT antenna VSAT VSAT systems (Very Small Aperture Terminal with very small aperture) provide satellite communication services to customers (usually small organizations) that do not require high bandwidth. The data rate for a VSAT is typically less than 2048 kbps. VSAT throughput The words “very small aperture” refer to the size of the terminal antennas when compared to the older antennas for backbone communication systems. VSATs operating in the C-band usually use antennas with a diameter of 1.8-2.4 m, in the Ku-band 0.75-1.8 m. VSAT systems use on-demand channel technology.
Initially, the emergence of satellite communications was dictated by the need to transfer large amounts of information. The first satellite communication system was the Intelsat system, then similar regional organizations were created (Eutelsat, Arabsat and others). Over time, the share of voice transmission in the total volume of backbone traffic has been steadily decreasing, giving way to data transmission. IntelsatEutelsatArabsat With the development of fiber-optic networks, the latter began to displace satellite communications from the backbone market.
A feature of most mobile satellite communication systems is the small size of the terminal antenna, which makes signal reception difficult. To ensure that the signal strength reaching the receiver is sufficient, one of two solutions is applied: The satellites are located in geostationary orbit. Since this orbit is at a distance of km from the Earth, a powerful transmitter must be installed on the satellite. This approach is used by the Inmarsat system (whose main task is to provide communication services to ships) and some regional personal satellite operators (for example, Thuraya). Earths Inmarsat Thuraya Many satellites are located in inclined or polar orbits. At the same time, the required transmitter power is not so high, and the cost of launching a satellite into orbit is lower.
However, this approach requires not only a large number satellites, but also an extensive network of ground switches. A similar method is used by operators Iridium and Globalstar.IridiumGlobalstar Mobile operators compete with personal satellite operators. Characteristically, both Globalstar and Iridium experienced serious financial difficulties, which brought Iridium to reorganization bankruptcy in 1999 Cellular communication bankruptcy In December 2006, an experimental geostationary satellite Kiku-8 was launched with a record large antenna area, which is supposed to be used to test the technology satellite communications with mobile devicesnot larger than cell phones. Kiku-8
Satellite communications are used in the organization of the "last mile" (a communication channel between an Internet provider and a client), especially in places with poorly developed infrastructure. The last mile by an Internet provider Features of this type of access are: Separation of incoming and outgoing traffic and attracting additional technologies for their combination. Therefore, such connections are called asymmetric. Simultaneous use of the incoming satellite channel by several (for example, 200) users: data is simultaneously transmitted via the satellite for all clients "interspersed", the client terminal is engaged in filtering unnecessary data (for this reason, "Fishing from satellite" is possible). the outgoing channel is distinguished:
Terminals working only for signal reception (the cheapest connection option). In this case, you need to have a different Internet connection for outgoing traffic, the provider of which is called the terrestrial provider. To work in such a scheme, a tunneling software, usually included in the delivery of the terminal. Despite the complexity (including the difficulty in setting up), this technology is attractive because of its high speed compared to dial-up for a relatively low price. Receiving and transmitting terminals. The outgoing channel is organized narrow (in comparison with the incoming). Both directions provide the same device, and therefore such a system is much easier to configure (especially if the terminal is external and connected to a computer via an Ethernet interface). Such a scheme requires the installation of a more complex (receiving-transmitting) converter on the antenna. In both cases, data from the provider to the client is transmitted, as a rule, in accordance with the digital broadcasting DVB, which allows you to use the same equipment both for network access and for receiving satellite television.
Poor noise immunity The huge distances between earth stations and a satellite cause the signal-to-noise ratio at the receiver to be very low (much less than for most radio relay links). In order to provide an acceptable error probability under these conditions, it is necessary to use large antennas, low-noise elements and complex error-correcting codes. This problem is especially acute in mobile communication systems, as they have restrictions on the size of the antenna and, as a rule, on the power of the transmitter. Antenna-immune codes Effect of the atmosphere The quality of satellite communications is strongly influenced by effects in the troposphere and ionosphere-troposphere-ionosphere
Tropospheric absorption The absorption of a signal by the atmosphere is dependent on its frequency. The absorption maxima are at 22.3 GHz (water vapor resonance) and 60 GHz (oxygen resonance). In general, absorption significantly affects the propagation of signals above 10 GHz (that is, starting from the Ku-band). In addition to absorption, during the propagation of radio waves in the atmosphere, there is a fading effect, which is caused by the difference in the refractive indices of different layers of the atmosphere. Resonance of water vapor, oxygen, fading, refractive indices Ionospheric effects Effects in the ionosphere are caused by fluctuations in the distribution of free electrons. Ionospheric effects that affect the propagation of radio waves include flickering, absorption, propagation delay, dispersion, frequency change, rotation of the plane of polarization. All of these effects diminish with increasing frequency. For signals with frequencies higher than 10 GHz, their influence is low fluctuations and dispersion
Propagation delay The problem of propagation delay affects all satellite communication systems in one way or another. Systems using a satellite transponder in geostationary orbit have the highest latency. In this case, the delay due to the finite propagation speed of radio waves is about 250 ms, and taking into account multiplexing, switching, and signal processing delays, the total delay can be up to 400 ms. Propagation delay is most undesirable in real-time applications such as telephony. Moreover, if the signal propagation time over the satellite communication channel is 250 ms, the time difference between the subscribers' replicas cannot be less than 500 ms.
