Communications satellites launched into space, as a rule, enter geostationary orbits, that is, they fly at the speed of the Earth's rotation and end up in an unchanged position with respect to the planet's surface. Circulating at an altitude of 22,300 miles above the equator, one such satellite can receive radio signals from one third of the planet.

The original satellites, such as Echo, launched into orbit in 1960, simply reflected radio signals directed at them. Advanced models not only receive signals, but also amplify them and transmit them to specified points on the earth's surface. Since the launch of the first commercial INTELSAT communications satellite in 1965, these devices have grown in complexity. The latest model of a satellite operating on solar energy, operates with 30,000 telephone calls or serves four television programs at the same time. The signals come from the antennas of the Earth-LA communication station and are received by the satellite transponder. This electronic device amplifies the signal and switches it to an antenna, which transmits it to the nearest LA-Earth communication station. In order to avoid interference, the up and down signals are transmitted at different frequencies.

Launched into geostationary orbits, three INTELSAT satellites (left) transmit longwave radio signals around the world. Serving the regions of the Pacific, Indian and Atlantic Oceans, satellites make high-speed telephone, television and telegraph communications possible. In this regard, high frequency radio signals lose out as they repel the charged particles that make up the E and F layers of the atmosphere.

This dish antenna can receive even very weak satellite signals, most similar systems can also serve for Earth-LA communications.

INTELSAT-6

Radio signals arriving at the satellite gradually weaken over a long journey to such a level that they can hardly be transmitted back to Earth. Satellites such as INTELSAT, modeled above, amplify incoming signals using solar power. Each satellite also has a supply of solid propellant to keep it in its orbit.

Pictured at the top of the article:

1. solar power cell
2. parabolic reflectors
3. parabolic reflectors
4. parabolic reflectors
5. parabolic reflectors

Like terrestrial antennas, this satellite dish consists of a tooth-like device called the primary emitter and a reflective parabolic shield. Two elements of this system ensure the reception of incoming radio waves and the destruction of alien waves.

Stations located on the surface of the planet interact with INTELSAT through huge, 30 feet wide parabolic antennas, similar to the one shown in Fig. above.

MODERN SATELLITES AND SATELLITE SYSTEMS

Main types of satellites

In the modern world, the inhabitants of our planet are already actively using the achievements of space technology. Scientific satellites, such as the Hubble Space Telescope, show us all the greatness and immensity of the space around us, the wonders that occur both in the remote corners of the Universe and in the nearest space.

Communication satellites such as, for example, Galaxy XI have received active use. With their participation, international and mobile telephone communications and, of course, satellite television are provided. Communications satellites play a huge role in the spread of the Internet. It is thanks to them that we have the opportunity with great speed to access information that is physically located on the other side of the world, on another continent.

Observation satellites, one of them "Spot", transmit information important for various industries and individual organizations, helping, for example, geologists to look for mineral deposits, administrations of large cities - to plan development, environmentalists - to assess the level of pollution of rivers and seas.

Airplanes, ships and vehicles are oriented using GPS and GLONASS satellites, and sea communications are controlled using navigation and communication satellites.

We are already accustomed to seeing pictures taken by satellites such as Meteosat in weather forecasts. Other satellites help scientists monitor conditions environment, transmitting information such as wave height and sea water temperature.

Military satellites provide the army and security agencies with the most various information, including electronic intelligence data from, for example, Magnum satellites, as well as very high-resolution imagery from secret optical and radar intelligence satellites.

In this section of the site, we will get acquainted with many satellite systems, the principles of their operation and the design of satellites.

Geostationary or Geosynchronous Clark Orbit

For the first time, the idea of ​​creating communication satellites originated shortly after the Second World War, when A. Clark in the October 1945 issue of the magazine "World of Radio" (Wireless World) presented in detail his concept of a relay communication station located at an altitude of 35880 km above the Earth's surface.

Such an orbit is called a geosynchronous, geostationary, or Clark orbit. The greater the height of the satellite's orbit, the longer the duration of one revolution around the Earth. When moving along a circular orbit with a height of 35880 km, one revolution is completed in 24 hours, i.e. during the Earth's daily rotation. A satellite moving in such an orbit will be constantly above a certain point on the Earth's surface (although regular orbit corrections will be required to compensate for the influence of the Moon's gravitational field).

Clark considered such an orbit ideal for global relay communications. Three satellites in geostationary orbit in the plane of the equator provide radio visibility to most of the Earth's surface (with the exception of the polar regions). This excludes the influence of the ionosphere on radio communications. Clark's idea was not immediately put into practice, because at that time there were no means of delivering a satellite even to low earth orbit, let alone stationary.

A. Clark submitted his initial proposals for a geostationary satellite to the Council of the British Interplanetary Society in the form of a memorandum. This document, dated May 25, 1945, is currently in the archives of the Smithsonian Institution in Washington.

Comstar 1 communication satellite

One of the first geostationary satellites used for the daily needs of people was the satellite Comstar. satellites Comstar 1 operator controlled Komsat and leased by AT&T. Their service life is estimated at seven years. They relay telephony and television signals within the United States as well as Puerto Rico. Through them, up to 6,000 telephone conversations and up to 12 television channels can be simultaneously relayed. The geometric dimensions of the satellite Comstar 1: height: 5.2 m (17 ft), diameter: 2.3 m (7.5 ft). Starting weight is 1,410 kg (3,109 lb).

Transceiver communication antenna with vertical and horizontal polarization gratings, allows both reception and transmission at the same frequency, but with perpendicular polarization. Due to this, the bandwidth of the radio frequency channels of the satellite is doubled. Looking ahead, we can say that the polarization of the radio signal is now used in almost all satellite systems, this is especially familiar to the owners of satellite receiving television systems, where when tuning to high-frequency TV channels, you have to set either vertical or horizontal polarization.

Another interesting design feature consists in the fact that the cylindrical body of the satellite rotates at a speed of about one revolution per second to provide the effect of gyroscopic stabilization of the satellite in space. If we take into account the considerable mass of the satellite - about one and a half tons - then the effect really takes place. And at the same time, the satellite antennas remain directed to a certain point in space on Earth in order to radiate a useful radio signal there.

At the same time, the satellite must be in geostationary orbit, i.e. "hang" over the Earth "stationary", more precisely, fly around the planet with the speed of its rotation around its own axis in the direction of its rotation. Departure from the positioning point due to the influence of various factors, the most significant of which are the interfering gravity of the Moon, encounters with cosmic dust and other space objects, is monitored by the control system and periodically corrected by the satellite's attitude control system engines.

Vladimir Kalanov, site "Knowledge is power".
Liter: Tim Furniss. The history of space vehicles.

Dear visitors!

Today there are two types of satellites: geostationary and low orbit. Geostationary satellites are called satellites in geostationary orbit. ( geostationary orbit- this is an orbit lying in the plane of the equator at an altitude of about 36 thousand km above the Earth's surface).

A satellite in geostationary orbit seems to be hanging motionless for an earth observer, and this opens up the possibility of using satellites as a television broadcast repeater. From an arbitrary point on the earth's surface, from which a geostationary satellite is visible, electromagnetic radiation from an earth transmitter can be directed to it. High frequencies are used as far as possible, of the order of 75-100 GHz (l 1 \u003d 3-4 mm) The use of shorter wavelengths is limited by strong atmospheric absorption in in the range of 300 GHz and above. The electromagnetic signal received on a geostationary satellite at a wavelength l 1 is converted to another, lower frequency of the order of 10 GHz (l 2 = 3 cm). This signal is sent to the earth's surface using another satellite antenna. For satellite transmitter to irradiate the Earth's surface, the satellite does not require a large-diameter antenna, since this radiation must be "smeared" on large area called the service area. It is important how the satellite maintains its geostationary position in orbit. If the satellite drifts, then it leaves, partially or completely, from the field of view of the ground receiving antenna. In this case, the television signal decreases, which is manifested in the disappearance of the image on the TV screen and the appearance of noise ("snow"). In such cases, it is necessary to correct the orientation of the terrestrial antenna - manually or automatically.

Geostationary satellites perform many tasks today, such as: telecommunications, radio positioning (systems gps navigation, glonass, etc.), the main task of most geostationary satellites is to form images of the visible earth's surface. Satellite communication systems with geostationary repeater satellites are ideal for solving such problems as organizing television and sound broadcasting over vast territories and providing high-quality telecommunications services to subscribers in remote and hard-to-reach regions. In addition, they can be used to quickly create large-scale corporate networks and reserve long-distance terrestrial backbone communication channels. Also, the creation of multi-service networks (combining such services as data transmission, telephony, digital television, videoconferencing and Internet access) based on VSAT technology is currently underway. It is also important to replace that only three geostationary satellites are capable of covering the entire surface of the Earth. But geostationary satellites also have disadvantages, the most important of which is: Too many communication satellites cannot be placed in geostationary orbit, otherwise they will interfere with each other's work. Therefore, in addition to geostationary satellites, which will soon “fill up” the geostationary orbit, it is necessary to develop other low-orbit satellite systems, which is happening now. As a rule, low-orbit satellite communication systems (SSS) (LEO systems) include those for which the orbit within 700-1500 km, the mass of satellites is up to 500 kg, the orbital constellation is from several units to dozens of repeater satellites (SR). Low orbit systems allow communication with terminals located in the polar latitudes, and have practically no alternative when organizing communication in regions with an underdeveloped communication infrastructure and low population density. The cost of mobile communication services by low earth orbit systems is several times cheaper than similar services provided by geostationary systems due to the use of inexpensive subscriber stations and less expensive space segment. . However, there are difficulties in managing the constellation of such satellites and maintaining communication continuity.

And in conclusion, I would like to say that modern optical-television space facilities already make it possible to view objects with dimensions of the order of a meter from orbit and transmit the resulting image through repeater satellites to subscribers.

Report on the topic:

Modern satellite communications, satellite systems.

Project content:

Introduction

3.Satellite communication system

4. Application of satellite communication

5.VSAT technology

7.Mobile satellite communication systems

8. Disadvantages of satellite communications

9. Conclusion

Introduction

Modern realities are already talking about the inevitability of satellite communications to replace the usual mobile ones, and even more so, landlines. The latest satellite communication technologies offer viable technical and cost-effective solutions for the development of both universal communication services and direct voice and TV broadcasting networks. Thanks to outstanding achievements in the field of microelectronics, satellite phones have become so compact and reliable in use that all the demands are being made by various user groups, and the satellite rental service is one of the most demanded services in the modern satellite communications market. Significant development prospects, obvious advantages over other telephony, reliability and guaranteed uninterrupted communication - all this is about satellite phones.

Satellite communication today is the only cost-effective solution for providing communication services to subscribers in areas with low population density, which is confirmed by a number of economic studies. The satellite is the only technically feasible and cost-effective solution if the population density is lower than 1.5 people/km2.Satellite communication has the most important advantages necessary for building large-scale telecommunication networks. Firstly, it can be used to quickly form a network infrastructure that covers a large area and does not depend on the presence or condition of terrestrial communication channels. Secondly, the use of modern technologies for accessing the resource of satellite repeaters and the possibility of delivering information to an almost unlimited number of consumers at the same time significantly reduce the cost of network operation. These advantages of satellite communication make it very attractive and highly efficient even in regions with well-developed terrestrial telecommunications. Preliminary forecasts for the development of personal satellite communication systems show that at the beginning of the 21st the number of their subscribers amounted to approximately 1 million, and over the next decade - 3 million. Currently, the number of users of the Inmarsat satellite system is 40,000.

In recent years, modern types and means of communication have been increasingly introduced in Russia. But, if a cellular radiotelephone has already become familiar, then a personal satellite communication device (satellite terminal) is still a rarity. An analysis of the development of such means of communication shows that in the near future we will witness the daily use of personal satellite communication systems (SPSS). The time is approaching for the unification of terrestrial and satellite systems into a global communications system. Personal communication will become possible on a global scale, i.e., the reach of the subscriber anywhere in the world will be ensured by dialing his telephone number, regardless of the location of the subscriber. But before this becomes a reality, satellite communication systems will have to successfully pass the test and confirm the claimed specifications and economic performance and the process of commercial exploitation. As for consumers, in order to make the right choice, they will have to learn how to navigate well in a variety of offers.

Project goals:

1. Study the history of the satellite communication system.

2. Familiarize yourself withfeatures and prospects for the development and design of satellite communications.

3. Get information about modern satellite communications.

Project objectives:

1. Analyze the development of a satellite communication system at all its stages.

2. Get a complete understanding of modern satellite communications.

1. Development of a satellite communication network

At the end of 1945, the world saw a small scientific article, which was devoted to the theoretical possibilities of improving communication (primarily, the distance between the receiver and transmitter) by raising the antenna to its maximum height. The use of artificial satellites as repeaters of radio signals became possible thanks to the theory of the English scientist Arthur Clark, who published a note entitled "Extraterrestrial repeaters" in 1945. He actually foresaw a new round in the evolution of radio relay communications, proposing to bring repeaters to the maximum available height.

American scientists became interested in theoretical research, who saw in the article a lot of advantages from a new type of connection:

no need to build a chain of terrestrial repeaters anymore;

one satellite is enough to provide a large coverage area;

the possibility of transmitting a radio signal to anywhere in the world, regardless of the availability of telecommunications infrastructure.

As a result, practical research and the formation of a satellite communications network around the world began in the second half of the last century. As the number of repeaters in orbit grew, new technologies were introduced and equipment for satellite communications improved. Now this method of information exchange has become available not only to large corporations and military companies, but also to individuals.

The development of satellite communication systems began with the launch of the first Echo-1 apparatus (a passive repeater in the form of a metallized ball) into space in August 1960. Later, key satellite communication standards (operating frequency bands) were developed and are widely used throughout the world.

1.1 The history of the development of satellite communications and the main types of communications

The history of the development of the Satellite Communication System has five stages:

1957-1965 The preparatory period, which began in October 1957 after the launch by the Soviet Union of the world's first artificial Earth satellite, and a month later, the second. This happened at the height of the Cold War and the rapid arms race, so, naturally, satellite technology became the property of the military in the first place. The stage under consideration is characterized by the launch of early experimental satellites, including communication satellites, which were mainly launched into low Earth orbits.

The first geostationary relay satellite TKLSTAR was created in the interests of the US Army and launched into orbit in July 1962. During the same period of time, a series of US military communications satellites SYN-COM (Synchronous Communications Satellite) was developed.

1965-1973 The period of development of global SSN based on geostationary repeaters. The year 1965 was marked by the launch in April of the geostationary SR INTELSAT-1, which marked the beginning of commercial use satellite communications. Early satellites of the INTELSAT series provided transcontinental communications and mainly supported backbone communications between a small number of national gateway earth stations providing an interface to national public terrestrial networks.

The main channels provided connections through which telephone traffic, TV signals and telex communication was provided. In general, the Intelsat CCC complemented and backed up the submarine transcontinental cable communication lines that existed at that time.

1973-1982 The stage of wide dissemination of regional and national CCC. At this stage of the historical development of the CCC, the international organization Inmarsat was created, which deployed global network Inmarsat communications, the main purpose of which was to provide communications with ships at sea. Later, Inmarsat extended its services to all types of mobile users.

1982-1990 The period of rapid development and spread of small earth terminals. In the 1980s, advances in engineering and technology of the key elements of the CCC, as well as reforms to liberalize and demonopolize the communications industry in a number of countries made it possible to use satellite channels in corporate business communication networks, called VSAT.

VSAT networks made it possible to install compact satellite earth stations in the immediate vicinity of user offices, thereby solving the “last mile” problem for a huge number of corporate users, created conditions for a comfortable and efficient exchange of information, and made it possible to offload public terrestrial networks. The use of “smart” satellites connections.

From the first half of the 1990s, the SSS entered a quantitatively and qualitatively new stage in its development.

A large number of global and regional satellite communications networks were in operation, production or design. Satellite communications technology has become an area of ​​significant interest and business activity. During this time period, there was an explosion in the speed of general purpose microprocessors and the volume of semiconductor storage devices, while improving the reliability, as well as reducing the power consumption and cost of these components.

Main types of communication

Given the wide scope, I will highlight the most common types of communication that are currently used in our country and around the world:

radio relay;

high frequency;

postal;

GSM;

satellite;

optical;

control room.

Each type has its own technology and complex necessary equipment for full functionality. I will consider these categories in more detail.

Communication via satellite

The history of satellite communications begins at the end of 1945, when British scientists developed the theory of transmitting a radio relay signal through repeaters that would be at high altitude (geostationary orbit). The first artificial satellites began to be launched in 1957.

The advantages of this type of connection are obvious:

the minimum number of repeaters (in practice, one or two satellites are enough to provide high-quality communications);

improvement of the basic characteristics of the signal (no interference, increased transmission distance, improved quality);

increase in coverage area.

Today, satellite communications equipment is a complex complex, which consists not only of orbital repeaters, but also base ground stations, which are located in different parts planets.

2. The current state of the satellite communication network

Of the many commercial MSS (Mobile Satellite) projects below 1 GHz, one Orbcomm system has been implemented, which includes 30 non-geostationary (non-GSO) satellites providing Earth coverage.

Due to the use of relatively low frequency bands, the system allows the provision of low-speed data transmission services to simple, low-cost subscriber devices, such as Email, two-way paging, remote control services. The main users of Orbcomm are transport companies, for which this system provides a cost-effective solution for the control and management of cargo transportation.

The most well-known operator in the MSS market is Inmarsat. There are about 30 types of subscriber devices on the market, both portable and mobile: for land, sea and air use, providing voice, fax and data transmission at speeds from 600 bps to 64 kbps. Inmarsat is competing with three MSS systems, including Globalstar, Iridium and Thuraya.

The first two provide almost complete coverage of the earth's surface through the use of large constellations, respectively, consisting of 40 and 79 non-GSO satellites. Pre Thuraya went global in 2007 with the launch of a third geostationary (GEO) satellite that will cover the Americas where it is currently unavailable. All three systems provide services telephone connection and low-speed data transmission to receiving devices comparable in weight and size to mobile phones GSM.

The development of satellite communication systems plays a significant role in the formation of a unified information space on the territory of the state and is closely connected with federal programs to eliminate the digital divide, the development of nationwide infrastructure and social projects. The most significant Federal targeted programs on the territory of the Russian Federation are projects on "Development of television and radio broadcasting" and "Elimination of digital inequality". The main tasks of the projects are the development of digital terrestrial television, communication networks, systems of mass broadband access to global information networks and provision of multi-service services on mobile and mobile objects. Apart from federal projects, the development of satellite communication systems provides new opportunities for solving the problems of the corporate market. The fields of application of satellite technologies and various satellite communication systems are rapidly expanding every year.

One of the key factors in the successful development of satellite technologies in Russia is the implementation of the Program for the Development of the Orbital Constellation of Civil Communication and Broadcasting Satellites, including satellites in highly elliptical orbits.

Development of satellite communication systems

The main drivers for the development of the satellite communications industry in Russia today are:

launch of networks in the Ka-band (on Russian satellites "EXPRES-AM5", "EXPRES-AM6"),

active development of the segment of mobile and mobile communications on various transport platforms,

entry of satellite operators into the mass market,

development of solutions for organizing backbone channels for cellular communication networks in the Ka-band and M2M applications.

The general trend in the global satellite services market is the rapid growth of data transfer rates provided on satellite resources, which meets the basic requirements of modern multimedia applications and responsive to development software and growth in the volume of transmitted data in the corporate and private segments.
In satellite communication networks operating in the Ka-band, the greatest interest is associated with the development of services for the private and corporate segment in the face of decreasing cost of satellite capacity implemented on Ka-band satellites with high bandwidth (High-Throughput Satellite - HTS).

Use of satellite communication systems

Satellite communication systems are designed to meet the needs of communication and satellite Internet access anywhere in the world. They are needed where increased reliability and fault tolerance are required, they are used for high-speed data transmission in organizing multi-channel telephone communication.

Specialized communication systems have a number of advantages, but the key is the ability to implement high-quality telephony outside the coverage areas of cellular communication stations.

Such communication systems make it possible to operate from autonomous power for a long time and be in call waiting mode, this happens due to the low energy performance of user equipment, light weight and an omnidirectional antenna.

Currently, there are many different satellite communication systems. All have their pros and cons. Additionally, each manufacturer offers users an individual set of services (Internet, fax, telex), defines a set of functions for each coverage area, and also calculates the cost of satellite equipment and communication services. In Russia, the key ones are:Inmarsat, Iridium and Thuraya.

Spheres of use of SSS (Satellite communication systems): navigation, ministries and departments, governing bodies of state structures and institutions, the Ministry of Emergency Situations and rescue units.

The world's first mobile satellite communication system offering a full range of modern services to users around the world:, and in the spirit.

Satellite communication system Inmarsat (Inmarsat) has a number of advantages:

coverage area - the entire territory of the globe, except for the polar regions

the quality of the services provided

confidentiality

additional accessories (car kits, fax machines, etc.)

free incoming calls

availability in use

online system for checking account status (billing)

high level of trust among users, time-tested (more than 25 years of existence and 210 thousand users worldwide)

The main services of the satellite communication system Inmarsat (Inmarsat):

Telephone

Fax

Email

Data transfer (including high-speed)

Telex (for some standards)

GPS

First in the world global system satellite communication that operates anywhere in the world, including the regions of the South and North Poles. The manufacturer offers a universal service available for business and life at any time of the day.

The satellite communication system Iridium (Iridium) has a number of advantages:

coverage area - the entire territory of the globe

low tariff plans

free incoming calls

The main services of the Iridium satellite communication system (Iridium) :

Telephone

Data transfer

Paging

satellite operator, which provides service to 35% of the globe. Services implemented in this system: satellite and GSM handsets, as well as satellite payphones. Inexpensive mobile connection for freedom of communication and movement.

Thuraya satellite communication system has a number of advantages:

compact size

the ability to switch between satellite and cellular communications automatically

low cost of services and telephone sets

free incoming calls

The main services of the Thuraya satellite communication system:

Telephone

Email

Data transfer

GPS

3.Satellite communication system

3. 1. Satellite repeaters

For the first time years of research, passive satellite transponders were used (examples are the Echo and Echo-2 satellites), which were a simple radio signal reflector (often a metal or polymer sphere with a metal coating) that did not carry any transceiver equipment on board. Such satellites have not received distribution.

3.2 Orbits of satellite transponders

The orbits in which satellite transponders are located are divided into three classes:

equatorial

inclined

polar

An important variation of the equatorial orbit is the geostationary orbit, in which the satellite rotates with an angular velocity equal to the angular velocity of the Earth, in a direction that coincides with the direction of the Earth's rotation.

An inclined orbit solves these problems, however, due to the movement of the satellite relative to the ground observer, it is necessary to launch at least three satellites per orbit in order to provide round-the-clock communication access.

Polar - an orbit that has an orbital inclination to the plane of the equator of ninety degrees.

4.VSAT system

Among satellite technologies, special attention is drawn to the development of satellite communication technologies such as VSAT (Very Small Aperture Terminal).

On the basis of VSAT equipment, it is possible to build multiservice networks that provide almost all modern communication services: Internet access; telephone connection; Union local networks(building VPN networks); transmission of audio and video information; redundancy of existing communication channels; data collection, monitoring and remote control industrial facilities and much more.

A bit of history. The development of VSAT networks begins with the launch of the first communications satellite. In the late 60s, in the course of experiments with the ATS-1 satellite, an experimental network was created, consisting of 25 earth stations, satellite telephone communications in Alaska. Linkabit, one of the original creators of Ku-band VSAT, merged with M/A-COM, which later became the leading supplier of VSAT equipment. Hughes Communications acquired the division from M/A-COM, transforming it into Hughes Network Systems. On this moment Hughes Network Systems is the world's leading provider of broadband satellite communications networks. A VSAT-based satellite communications network includes three key elements: a central control station (CCS), a repeater satellite, and subscriber VSAT terminals.

4.1.Satellite repeater

VSAT networks are built on the basis of geostationary repeater satellites. The most important characteristics satellite are the power of the onboard transmitters and the number of radio frequency channels (trunks or transponders) on it. The standard barrel has a bandwidth of 36 MHz, which corresponds to the maximum bandwidth about 40 Mbps. On average, the power of transmitters ranges from 20 to 100 watts. In Russia, Yamal communication and broadcasting satellites can be cited as examples of repeater satellites. They are intended for the development of the space segment of OAO Gascom and were installed in orbital positions 49°E. d. and 90 ° in. d.

4.2 Subscriber VSAT terminals

Subscriber VSAT terminal is a small satellite communication station with an antenna with a diameter of 0.9 to 2.4 m, designed mainly for reliable data exchange via satellite channels. The station consists of an antenna-feeder device, an outdoor external radio frequency unit and an indoor unit (satellite modem). The outdoor unit is a small transceiver or just a receiver. The indoor unit provides pairing of the satellite channel with the user's terminal equipment (computer, LAN server, telephone, fax, etc.).

5. VSAT technology

There are two main types of access to a satellite channel: two-way (duplex) and one-way (simplex, asymmetric or combined).

When organizing one-way access, along with satellite equipment, a terrestrial communication channel (telephone line, fiber optic, cellular networks, radio ethernet) is necessarily used, which is used as a request channel (it is also called a reverse channel).

One-way access scheme using a DVB-card and telephone line as a return channel.

Two-way access scheme using HughesNet equipment (Hughes Network Systems).

Today in Russia there are several significant operators VSAT networks that serve about 80,000 VSATs. 33% of such terminals are located in the Central Federal District, 13% each in the Siberian and Ural Federal Districts, 11% in the Far East and 5-8% each in the other federal districts. Among the largest operators it is worth highlighting:

6.Global satellite communication system Globalstar

In Russia, the operator of the satellite communication system Globalstar is the Closed Joint Stock Company GlobalTel. As the exclusive provider of global mobile satellite communication services of the Globalstar system, CJSC GlobalTel provides communication services throughout the Russian Federation. Thanks to the creation of CJSC "GlobalTel", the inhabitants of Russia have another opportunity to communicate via satellite from anywhere in Russia to almost anywhere in the world.

The Globalstar system provides satellite communications High Quality for its subscribers with the help of 48 working and 8 spare low-orbit satellites located at an altitude of 1410 km. (876 miles) from the Earth's surface. The system provides global coverage of almost the entire surface of the globe between 700 North and South latitudes with an extension of up to 740. Satellites are capable of receiving signals up to 80% of the Earth's surface, i.e. from almost anywhere on the globe, with the exception of the polar regions and some areas of the central part of the oceans . The satellites of the system are simple and reliable.

6.1. Areas of application of the Globalstar system

The Globalstar system is designed to provide high quality satellite services to a wide range of users including: voice communication, short message service, roaming, positioning, facsimile, data, mobile Internet.

Subscribers using portable and mobile devices can be business and individuals working in territories that are not covered cellular networks, or the specifics of which work involves frequent business trips to places where there is no connection or poor quality of communication.

The system is designed for a wide consumer: representatives of the media, geologists, workers in the extraction and processing of oil and gas, precious metals, civil engineers, power engineers. Employees of state structures of Russia - ministries and departments (for example, the Ministry of Emergency Situations) can actively use satellite communications in their activities. Special kits for installation on vehicles can be effective when used on commercial vehicles, fishing and other types of sea and river vessels, railway transport, etc.

7.1. Mobile satellite communication systems

A feature of most mobile satellite communications systems is the small size of the terminal antenna, which makes signal reception difficult. In order for the signal strength reaching the receiver to be sufficient, one of two solutions is applied:

The satellites are in geostationary orbit. Since this orbit is 35,786 km away from the Earth, a powerful transmitter is required on the satellite. This approach is used by the Inmarsat system (whose main task is to provide communications services to ships) and some regional personal satellite communications operators (for example, Thuraya).

7.1. Satellite Internet

Satellite Internet - a way to provide access to the Internet using satellite communication technologies (usually in DVB-S standard or DVB-S2).

Access options

There are two ways to exchange data via satellite:

• one-way (one-way), sometimes also called "asymmetric" - when a satellite channel is used to receive data, and available terrestrial channels are used for transmission

  two-way (two-way), sometimes also called "symmetrical" - when satellite channels are used for both reception and transmission;

One way satellite Internet

One-way satellite Internet implies that the user has some existing way to connect to the Internet. As a rule, this is a slow and / or expensive channel (GPRS / EDGE, ADSL connection where Internet access services are poorly developed and speed limited, etc.). Only requests to the Internet are transmitted through this channel.

Two way satellite Internet

Two-way satellite Internet means receiving data from the satellite and sending it back also via the satellite. This method is of very high quality, as it allows you to achieve high speeds during transmission and sending, but it is quite expensive and requires permission for radio transmitting equipment (however, the provider often takes care of the latter). The high cost of two-way Internet is fully justified due to the much more reliable connection in the first place. Unlike one-way access, two-way satellite Internet does not require any additional resources (other than power, of course).

A feature of "two-way" satellite Internet access is a sufficiently large delay on the communication channel. Until the signal reaches the subscriber to the satellite and from the satellite to the Central satellite communication station, it will take about 250 ms. The same amount is needed for the trip back. Plus, the inevitable delays in signal processing and in order to go "over the Internet". As a result, the ping time on a two-way satellite link is about 600 ms or more. This imposes some specifics on the operation of applications via satellite Internet and is especially sad for avid gamers.

Another feature is that equipment from different manufacturers is practically incompatible with each other. That is, if you have chosen one operator working on a certain type of equipment (for example, ViaSat, Hughes, Gilat EMS, Shiron, etc.), then you can only go to the operator using the same equipment. An attempt to implement the compatibility of equipment from different manufacturers (DVB-RCS standard) was supported by a very small number of companies, and today it is more of a "private" technology than a generally accepted standard.

Equipment for unilateral satellite internet

8. Disadvantages of satellite communications

Weak noise immunity

The huge distances between earth stations and the satellite cause the signal-to-noise ratio at the receiver to be very low (much less than for most microwave 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 a limit on the size of the antenna and, as a rule, on the power of the transmitter.

Influence of the atmosphere

The quality of satellite communication is strongly influenced by effects in the troposphere and ionosphere.

Absorption in the troposphere

The absorption of a signal by the atmosphere depends 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 (i.e., starting from the Ku-band). In addition to absorption, during the propagation of radio waves in the atmosphere, there is a fading effect, the cause of which is the difference in the refractive indices of different layers of the atmosphere.

Ionospheric effects

Propagation Delay

The problem of signal propagation delay, one way or another, affects all satellite communication systems. Systems using a satellite transponder in geostationary orbit have the highest latency. In this case, the delay due to the finiteness of the radio wave propagation speed is approximately 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. In this case, if the signal propagation time over the satellite communication channel is 250 ms, the time difference between subscribers' replicas cannot be less than 500 ms. In some systems (eg, VSAT systems using a star topology), the signal is transmitted twice via a satellite link (from a terminal to a central site, and from a central site to another terminal). In this case, the total delay is doubled.

9. Conclusion

Already at the earliest stages of creating satellite systems, the complexity of the work ahead became obvious. It was necessary to find financial means, apply the intellectual efforts of many teams of scientists, organize work at the stage practical implementation. But, despite this, transnational companies with free capital are actively involved in solving the problem. Moreover, not one, but several parallel projects are currently being implemented. Firms-developers are stubbornly competing for future consumers, for world leadership in the field of telecommunications.

At present, satellite communication stations are combined into data transmission networks. Combining a group of geographically distributed stations into a network makes it possible to provide users with a wide range of services and opportunities, as well as to effectively use satellite resources. In such networks, there is usually one or more control stations that provide operation of earth stations in both administrator-managed and fully automatic modes.

The advantage of satellite communications is based on serving geographically distant users without additional costs for intermediate storage and switching.

SSNs are constantly and jealously compared to fiber optic communication networks. The introduction of these networks is accelerating due to the rapid technological development of the relevant areas of fiber optics, which raises questions about the fate of the SSN. For example, development and planning, most importantly, the introduction of concatenating (composite) coding dramatically reduces the likelihood of an uncorrected bit error, which, in turn, allows you to overcome the main problem of CCC - fog and rain.

12. List of sources used

Baranov V. I. Stechkin B. S. Extremal combinatorial problems and their

applications, M.: Nauka, 2000, p. 198.

Bertsekas D. Gallagher R. Data transmission networks. M.: Mir, 2000, p. 295.

Black Yu. Computer networks: protocols, standards, interfaces, M.: Mir, 2001, p. 320.

Bolshova G. "Satellite communications in Russia: "Pamir", Iridium, Globalstar..." "Networks" - 2000 - №9. - With. 20-28.

Efimushkin V. A. Technical aspects satellite communication systems "Networks" - 2000 - No. 7. - With. 19-24.

Nevdyaev L. M. Modern technologies of satellite communication // "Bulletin of Communications" - 2000 - No. 12. - p. 30-39.

Nevdyaev L. M. Odyssey at medium heights of the "Network" - 2000 - No. 2. - With. 13-15.

SPC "Elsov", Protocol on the organization and logic of the satellite data transmission network "Banker". – 2004, p. 235.

Smirnova A. A. Corporate satellite and HF communication systems Moscow, 2000, p.

Smirnova A. A. Personal satellite communication, Volume 64, Moscow, 2001, p.

Space or satellite communication is essentially a kind of radio relay (tropospheric) communication and differs in that its repeaters are not on the surface of the Earth, but on satellites in outer space.

The idea of ​​satellite communications was first introduced in 1945 by the Englishman Arthur Clark. In a radio engineering journal, he published an article on the prospects of rockets like the V-2 for launching Earth satellites for scientific and practical purposes. The last paragraph of this article is significant: “An artificial satellite at a certain distance from the Earth will make one revolution in 24 hours. It will remain motionless over a certain place and within optical visibility from almost half of the earth's surface. Three repeaters, placed in a well-chosen orbit with an angular separation of 120°, will be able to cover the entire planet with TV and VHF radio broadcasts; I am afraid that those who plan post-war work will not consider this a simple matter, but I consider this way to be the final solution to the problem.

On October 4, 1957, the USSR launched the world's first artificial Earth satellite, the first space object whose signals were received on Earth. This satellite marked the beginning of the space age. The signals emitted by the satellite were used not only for direction finding, but also for transmitting information about the processes on the satellite (temperature, pressure, etc.). This information was transmitted by changing the duration of the messages emitted by the transmitters (pulse width modulation). On April 12, 1961, for the first time in the history of mankind, a manned flight into outer space was carried out in the Soviet Union. The spacecraft "Vostok" with pilot-cosmonaut Yu. A. Gagarin on board was put into orbit as an Earth satellite. Numerous measuring and radiotelemetric equipment were installed on board to measure the parameters of the orbit of the satellite and control the operation of its onboard equipment. For the direction finding of the ship and the transmission of telemetric information, the Signal radio system was used, operating at a frequency of 19.955 MHz. The astronaut's two-way communication with the Earth was provided by a radiotelephone system operating in the ranges of short (19.019 and 20.006 MHz) and ultrashort (143.625 MHz) waves. The television system transmitted the astronaut's image to Earth, which made it possible to have visual control over his condition. One of the television cameras transmitted the image of the pilot from the front, and the other from the side.

The achievements of domestic science in the field of space exploration made it possible to realize the predictions of Arthur C. Clarke. At the end of the 1950s, experimental studies began in the USSR and the USA on the possibilities of using artificial Earth satellites as radio repeaters (active and passive) in terrestrial communication systems. Theoretical developments in the field of energy capabilities of satellite communication lines made it possible to formulate tactical and technical requirements for satellite repeater devices and ground devices, based on the actual characteristics of the technical means that existed at that time.

Given the identity of the approaches, we will present experimental studies in the field of creating satellite communication lines using the example of the United States. The first active radio repeater "Score" was launched on December 18, 1958 into an inclined elliptical orbit with an apogee of 1481 km, a perigee of 177 km. The satellite equipment consisted of two transceivers operating at frequencies of 132.435 and 132.095 MHz. The work was carried out in the slow relay mode. The storage of the signal sent by the ground transmitting station was carried out by recording on magnetic tape. Silver-zinc batteries with a capacity of 45 ampere-hour at a voltage of 18 volts were used as power sources. The duration of communication was approximately 4 min per 1 revolution of the satellite. Retransmission of 1 telephone or 7 teletype channels was carried out. The lifetime of the satellite was 34 days. The satellite burned up on re-entry on January 21, 1959. The second active radio relay "Courier" was launched on October 4, 1960 into an inclined elliptical orbit with an apogee of 1270 km and a perigee of 970 km. The satellite equipment consisted of 4 transceivers (frequency 150 MHz for transmitting commands and 1900 MHz for communication), a magnetic memory device and power sources - solar cells and chemical batteries. Silicon solar cells in the amount of 19,152 pieces were used as the primary power source. Nickel-cadmium batteries with a capacity of 10 amperes - hour at a voltage of 28-32 volts were used as a buffer stage. The duration of the communication session was 5 min per one revolution of the satellite. The service life of the satellite was 1 year. On July 10, 1962, the Telstar active relay was launched into an inclined elliptical orbit with an apogee of 5600 km and a perigee of 950 km, which was intended for active relaying of radio signals in real time. At the same time, it relayed either 600 simplex telephone channels, or 12 duplex telephone channels, or one television channel. In all cases, the work was carried out according to the method of frequency modulation. Communication frequencies: on the satellite-Earth line 4169.72 MHz, on the Earth-satellite line 6389.58 MHz. The duration of the communication session on the US-Europe line via this satellite was about 2 hours per day. The quality of the transmitted television images varied from good to excellent. The project provided for a very significant satellite service life of 2 years, but after four months of successful operation, the command line failed. It was found that the cause of the failure was surface damage due to the action of radiation when the satellite passed through the inner radiation belt.

On February 14, 1963, the first synchronous satellite of the Sinkom system was launched with orbital parameters: apogee height 37,022 km, perigee height 34185, orbital period 1426.6 minutes. The operating frequency on the Earth-satellite line is 7360 MHz, on the satellite-Earth line is 1820 MHz. 3840 solar cells with a total power of 28 W at a voltage of 27.5 volts were used as the primary power source on the satellite. Communication with the satellite was maintained for only 20,077 seconds, after which observations were made by astronomical methods.

On April 23, 1965, the first communications satellite Molniya-1 was launched in the USSR. With the launch of the second communication satellite "Molniya-2" on October 14, 1965, regular operation of the long-distance communication line through satellites began. Later, the Orbita deep space communication system was created. It consisted of a network of ground stations and artificial Earth satellites "Lightning", "Rainbow", "Horizon". Below, in Chapter 7, it will be shown that modifications of the Horizon satellites continue to function in the 21st century. This indicates the high reliability of domestic equipment compared to foreign ones.

The first satellite communication stations were built, tested and put into operation in the town of Shchelkovo near Moscow and in Ussuriysk. By cable and relay communication lines, they were connected, respectively, with television centers and telephone long-distance stations in Moscow and Vladivostok.

The TR-60/120 tropospheric communication equipment, which, as is known, used high-power transmitters and highly sensitive receivers with low-noise parametric amplifiers, turned out to be the most suitable for the equipment of earth stations of the satellite system. On its basis, a receiver-transmitter complex "Horizont" is being developed, which is installed at ground stations of the first satellite communication line between Moscow and Vladivostok.

Specially designed transmitters for communication and command-measuring lines, parametric amplifiers with a noise temperature of 120 K for installation in the antenna under the mirror cabin, as well as completely new equipment that provides docking with local television centers and long-distance telephone exchanges.

In those years, earth station designers, fearing the influence of powerful transmitters on receivers, installed them on different antennas and in different buildings (receiving and transmitting). However, the experience of using one common antenna for receiving and transmitting, obtained on tropospheric communication lines, made it possible in the future to transfer the receiving equipment to the transmitting antenna, which greatly simplified and cheapened the operation of satellite communication stations.

In 1967, through the Molniya-1 communications satellite, an extensive television network of receiving earth stations "Orbita" was created with a central transmitting station near Moscow. This made it possible to organize the first communication channels between Moscow and the Far East, Siberia, Central Asia, to transmit the Central Television program to remote areas of our Motherland and to additionally cover more than 30 million viewers.

However, the Molniya satellites revolved around the Earth in elongated elliptical orbits. To track them, the antennas of ground receiving stations must constantly rotate. It is much easier to solve this problem by satellites rotating in a stationary circular orbit, which is located in the equatorial plane at an altitude of 36,000 km. They make one revolution around the Earth in 24 hours and therefore seem to a ground observer hanging motionless over one point of our planet. Three such satellites are enough to provide communications for the entire Earth.

In the 1980s, communication satellites "Raduga" and television satellites "Ekran" operating in stationary orbits effectively functioned. To receive their signals, complex ground stations were not needed. Television transmissions from such satellites are received directly on simple collective and even individual antennas.

In the 1980s, the development of personal satellite communications began. In this connection, a satellite phone is directly connected to a satellite in Earth orbit. From the satellite, the signal arrives at the ground station, from where it is transmitted to the conventional telephone network. The number of satellites required for stable communication anywhere in the world depends on the radius of the orbit of a particular satellite system.

The main disadvantage of personal satellite communications is its relative high cost compared to cellular communications. In addition, high power transmitters are built into satellite phones. Therefore, they are considered unsafe for the health of users.

The most reliable satellite phones operate on the Inmarsat network, established over 20 years ago. Inmarsat satellite phones are a flip-top case the size of the first laptop computers. Lid satellite phone concurrently, it is also an antenna that must be turned towards the satellite (the signal level is displayed on the phone display). These phones are mainly used on ships, trains or heavy vehicles. Every time you need to make or answer someone's call, you will need to install the satellite phone on some flat surface, open the lid and twist it, determining the direction of the maximum signal.

Currently, in the overall balance of communications, satellite systems still account for approximately 3% of world traffic. But the need for satellite links continues to grow, as satellite links become more cost-effective than other forms of long-distance communication at ranges in excess of 800 km.