Digital satellite communications. Satellite communication, types, system, equipment, means, orbits, satellite communication ranges. Areas of application of satellite communications

MODERN SATELLITES AND SATELLITE SYSTEMS

The main types of satellites

In the modern world, the inhabitants of our planet are already actively using the achievements of space technologies. Scientific satellites, such as the Hubble Space Telescope, demonstrate to us all the greatness and immensity of the space around us, miracles taking place both in remote corners of the Universe and in nearby space.

Communication satellites, such as, for example, Galaxy XI, are actively used. With their participation, international and mobile telephone communications and, of course, satellite television are provided. Communication 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 gain access to information that is physically located on the other side of the world, on another continent.

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

Airplanes, ships and cars are oriented using the satellites of the Global Positioning System (GPS) and GLONASS, and the control of maritime communications is carried out using navigation satellites and communication satellites.

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

Military satellites provide armies and security agencies with a variety of information, including electronic intelligence, such as Magnum satellites, and very high-resolution imagery, carried out by covert optical and radar reconnaissance satellites.

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

Clark's geostationary or geosynchronous orbit

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

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

Clarke considered such an orbit ideal for global relay communications. Three satellites in geostationary orbit in the equatorial plane provide radio visibility of most of the Earth's surface (with the exception of the circumpolar regions). This eliminates the influence of the ionosphere on radio communications. Clark's idea was not immediately implemented, since at that time there were no means of delivering a satellite even to low-earth orbit, let alone a stationary one.

A. Clark presented 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.

Communication satellite "Comstar 1"

One of the first geostationary satellites used for the daily needs of people was the satellite Comstar... Satellites Comstar 1 operated by the operator "Comsat" and rented by AT&T. Their service life is designed for 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 retransmitted. Geometric dimensions of the satellite Comstar 1: Height: 5.2 m (17 ft), Diameter: 2.3 m (7.5 ft). The starting weight is 1410 kg (3109 lb).

Transceiver communication antenna with vertical and horizontal polarization arrays, allows both receiving and transmitting at the same frequency, but with perpendicular polarization. This doubles the capacity of the satellite's radio frequency channels. 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 is 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 does indeed take place. And at the same time, the satellite antennas remain directed to a specific point in space on Earth in order to emit a useful radio signal there.

At the same time, the satellite must be in geostationary orbit, i.e. "to hang" above the Earth "motionless", more precisely, to 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 attraction of the Moon, encounters with cosmic dust and other objects in space, is monitored by the control system and periodically corrected by the engines of the satellite attitude control system.

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

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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, there is no need for a chain of repeaters. For transmission via satellite, the signal must be modulated. Modulation is performed at the earth station. The modulated signal is amplified, transferred to the desired frequency and fed to the transmitting antenna.

Research in the field of civil satellite communications in Western countries began to appear in the second half of the 50s of the XX century. The impetus for them was the increased demand for transatlantic telephony. The first artificial Earth satellite was launched in the USSR in 1957, however, due to the greater closedness of the space program, the development of satellite communications in the socialist countries proceeded differently than in the Western countries. For a long time, satellite communications were developed only in the interests of the USSR Ministry of Defense. 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, which were a simple reflector of a radio signal (often a metal or polymer sphere with a metal coating), which did not carry any transmitting and receiving 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 performing 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 modulates it again. Due to this, error correction is performed twice: on the satellite and on the receiving earth 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.

Communication satellite orbits:

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

1 - equatorial, 2 - oblique, 3 - polar

An important type of 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 rotation of the Earth. The obvious advantage of geostationary orbit is that the receiver in the service area "sees" the satellite all the time. 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 - the limiting case of inclined

When using inclined orbits, earth stations are equipped with tracking systems that aim the antenna at 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. The exception is small antennas used to receive satellite television: their radiation pattern is wide enough, so they do not sense satellite vibrations near the ideal point. A feature of most mobile satellite communication systems is the small size of the terminal antenna, which makes signal reception difficult.

A typical scheme for organizing satellite communications services is as follows:

• - the operator of the satellite segment creates a communications satellite at its own expense, placing an order for the manufacture of a satellite from one of the satellite manufacturers, and carries out its launch and maintenance. After launching the satellite into orbit, the satellite segment operator begins to provide services for leasing the frequency resource of the relay satellite to satellite communication service companies.
• - a satellite communications service operator concludes an agreement with a satellite segment operator for the use (lease) of capacities on a communications satellite, using it as a repeater with a large service area. An operator of satellite communications services builds the terrestrial infrastructure of its network on a certain technological platform produced by the companies that manufacture ground equipment for satellite communications.

Spheres of application of satellite communications:

• - Backbone satellite communications: initially, the emergence of satellite communications was dictated by the need for the transmission of 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. With the development of fiber-optic networks, the latter began to displace satellite communications from the backbone market.
• - VSAT systems: Very Small Aperture Terminal (VSAT) systems provide satellite communication services to customers (usually small organizations) that do not require high bandwidth. The data transfer rate for a VSAT terminal usually does not exceed 2048 kbps. The words "very small aperture" refer to the size of the terminal antennas relative to the size of the older backbone antennas. 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.
• - Mobile satellite systems: A feature of most mobile satellite systems is the small size of the terminal antenna, which makes signal reception difficult.

VSAT satellite communication principles:

A typical VSAT satellite network organization is as follows:

• - satellite repeater located in orbit (communication satellite)
• - the network control center (NCC) of the VSAT network operator, servicing the equipment of the entire network via a communication satellite
• - equipment (satellite modems or terminals) located on the client's side and interacting with the outside world or with each other through the HUB of the VSAT operator in accordance with the network topology

The main element of the satellite VSAT network is the NCC. It is the Network Control Center that provides access to client equipment from the Internet, public telephone network, other terminals of the VSAT network, and implements traffic exchange within the client's corporate network. The NCC has a broadband connection to backbone communication channels provided by backbone operators and provides information transfer from a remote VSAT terminal to the outside world. The NCC is equipped with a powerful receiving and transmitting complex that transmits all information flows of the network to the communication satellite. The NCC includes channel-forming equipment (satellite receiving and transmitting antenna, transceivers, etc.) and HUB (center for processing and switching all information in the VSAT network)

Technologies used in satellite communications:

multiple use of frequencies in satellite communications:

Since radio frequencies are a 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 only receives a signal from a specific area, and different areas 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 used twice (for each of the planes).

frequency ranges:

The choice of frequency for data transmission from earth station to satellite and from satellite to earth station is not arbitrary. Frequency affects, for example, the absorption of radio waves in the atmosphere, as well as the required dimensions of the transmitting and receiving antennas. The frequencies at which the transmission from the earth station to the satellite occurs differ from the frequencies used for the transmission from the satellite to the earth station (usually the former above). Frequencies used in satellite communications are divided into ranges designated by letters:

Range name		Application
		Mobile satellite communications
		Mobile satellite communications
	4 GHz, 6 GHz	Fixed satellite communications
	Frequencies are not defined for satellite communications in this range. For radar applications, the specified range is 8-12 GHz.	Fixed satellite communications (for military purposes)
	11 GHz, 12 GHz, 14 GHz
		Fixed satellite communications, satellite broadcasting
		Fixed satellite communications, inter-satellite communications

Ku-band allows reception with relatively small antennas, and therefore is used in satellite television (DVB), despite the fact that weather conditions in this band have a significant impact on the transmission quality. For data transmission by large users (organizations), the C-band is often used. This provides better reception, but requires a fairly large antenna size.

The painful problems are being solved by a chain of space stations with an orbital period of 24 hours, occupying an altitude of 42,000 km relative to the center of the Earth ... in the equatorial plane.

A. Clark, 1945.

In the Stone Age, a coherent network works by repeating actions to regulate the amount of smoke emitted by a fire. The earth knew runners, Little Muck became the best. The modern system uses spacecraft. The advantage of the satellite is the large coverage of the territory. Waves are used mainly short, capable of propagating in a straight line. The world is one - prices are everywhere ...

Prerequisites for use

The idea of ​​rebroadcasting was conceived by Emile Guarini-Foresio in 1899. The concept of mediated signal transmission was published by the German Journal for Electrical Engineering (volume 16, 35-36). Arthur Clarke in 1945 voiced the concept of a communication system between geostationary spacecraft. The writer refused to take a patent, rejecting two conclusions:

1. Low likelihood of the idea being implemented.
2. The need to give the idea to humanity as a whole.

At the same time, the scientist indicated the coordinates of the best coverage of areas of the planet's surface:

• 30 degrees East - Africa, Europe.
• 150 degrees East - China, Oceania.
• 90 degrees W. - America.

The writer lowered the operating frequency, expressing his intention to use 3 MHz by reducing the hypothetical reflectors (a few feet).

Ground-based microwave systems

The Anglo-French consortium, led by André Clavier, went further. The first successful attempts to use the microwave range of communication date back to 1931. The English Channel demonstrated the transmission of information at the frequency of 1.7 GHz (modern cellular band) for 64 kilometers by stations equipped with 3 meters diameter dishes, connecting Dover and Calais.

Interesting! The first commercial VHF television channel used 300 MHz.

Historians tend to view World War II as the horse that brought the industry to the top. The invention of the klystron and the improvement of technologies for the manufacture of paraboloids made an invaluable contribution. The heyday of transatlantic relations dates back to the 1950s.

For reference! The first relay line, formed by eight repeaters, New York - Boston, was built in 1947.

America and Europe have established the transmission of information by repeaters (radio communication, called relay). Commercial broadcasting began immediately. A feature of microwave communication is called the ability to accurately predict the result already at the stage of system design.

For reference! Relay communication is a technology for transmitting digital, analog signals between receivers in the field of view.

Spacecraft

The first Soviet satellite (1957) carried communication equipment. Three years later, the Americans raised an inflatable balloon to a height of 1,500 km, which served as a passive repeater, thanks to the metallized coating of the sphere. On August 20, 1964, 11 countries, including the USSR, signed an agreement on the creation of Intelsat (international communications). The Soviet bloc followed the path of secrecy while the West made money. The Eastern Bloc created its own program in 1971.

The satellites were a real find, allowing you to connect the opposite shores of the ocean. Optical fiber is an alternative.

The military was the first to launch the dark horse along with tropospheric communication, which used the effect of wave reflection by the upper layers. The Soviet microwave communications were intercepted by the celestial group Rhyolite. A system developed for the CIA (USA). The device took up a position captured by a ground beam of Soviet relay communications, recording messages. The territories of China and Eastern Europe were controlled. The diameter of the umbrella-like reflectors reached 20 meters.

The US leadership has always known the intentions of the leaders of the USSR, listening to everything, including phone calls. Today, satellite systems allow, thanks to the Doppler effect, to remotely attend any "confidential" conversations held in rooms equipped with a typical glass unit.

The first attempts to implement Nikola Tesla's ideas in space are registered: wireless transmission of electricity by satellite antennas. The epic started in 1975. Now the concept has returned home. The Wardencliffe Tower has long since been destroyed, but the main island of Hawaii received its 20 watts wirelessly.

For reference! The use of space communications has proven to be an economically viable alternative to optical fiber.

Signal features

No wonder the use of satellites, with that said.

Transparency windows

The phenomenon of absorption of waves by the atmosphere has been known for a long time. Scientists, having studied the phenomenon, concluded:

• Signal attenuation is determined by frequency.
• Transparency windows are observed.
• The phenomenon is modulated by weather conditions.

For example, the millimeter range (30-100 GHz) is heavily suppressed by rain. The vicinity of the 60 GHz frequency absorbs oxygen molecules, 22 GHz - water. Frequencies below 1 GHz are cut off by radiation from the galaxy. Temperature noise of the atmosphere has a negative impact.

The foregoing explains the choice of modern space communication frequencies. A complete list of the characteristics of the Ku-band signal is shown in the figure.

The C-band is also used.

Reception areas

A ray, crossing the surface of the Earth, forms isotropic curves of equivalent reception. The total losses are:

1. 200 dB - C-band.
2. 206 dB - Ku-band.

Solar interference can interfere with bagging. The worst conditions lasting 5-6 days are created by the off-season (winter, autumn). The luminary interference provides ground station technicians with guaranteed work. Tracking systems are turned off for the duration of a natural phenomenon. Otherwise, the plates can catch the Sun, giving the wrong commands to the on-board stabilization systems. Banks, airports are warned: communications will be temporarily disrupted.

Fresnel zones

Obstacles around the communication tower provoke the addition of waves, forming zones of attenuation / rise of the signal. The phenomenon explains the need for a clean space near the transceiver. Fortunately, microwave ovens are devoid of this drawback. Thanks to an important feature, every summer resident catches NTV + with a plate.

Flicker

Unpredictable changes in the atmosphere cause the signal to constantly change. Fluctuations up to 12 dB in amplitude affect a 500 MHz bandwidth. The phenomenon lasts 2-3 hours maximum. Flickering prevents ground stations from tracking the satellite, requiring preventive action.

Beam linearity

A feature of the microwave is considered to be a rectilinear ray trajectory. The phenomenon allows you to concentrate power, lowering the requirements for on-board systems. Surely the first task was espionage. Later, antennas ceased to be narrowly directed, covering vast territories, such as Russia.

Engineers call the property a disadvantage: it is impossible to go around mountains, ravines.

Features of wave addition

There is practically no interference pattern. It is possible to significantly compact adjacent frequency channels.

Capacity

Kotelnikov's theorem defines the upper limit of the spectrum of the transmitted signal. The threshold is directly set by the carrier frequency. Microwave, due to its high values, contain up to 30 times more information than VHF.

The possibility of regeneration

The development of digital technologies has opened the way for error correction techniques. Artificial satellite:

• received a weak signal;
• decoded;
• fixed bugs;
• coded;
• passed on.

The excellent quality of satellite communications has become a “talk of the tongue”.

Terrestrial antennas

Satellite dishes are called paraboloids. The diameter reaches 4 meters. In addition to the above, there are 2 types of relay communication antennas (both terrestrial):

1. Dielectric lenses.
2. Horn antennas.

Paraboloids provide high selectivity, allowing a beam to travel thousands of kilometers to establish communication. A typical cymbal is not capable of transmitting a signal; higher performance is required.

Operating principle

Spy satellites were constantly moving, providing relative invulnerability and secrecy of surveillance. The use of peaceful technologies took a different path. Clark's concept implemented:

• The equatorial orbit is home to hundreds of geostationary satellites.
• The stability of the position provides ease of pointing ground equipment.
• The orbital altitude (35786 meters) is fixed, since it is necessary to balance the earth's gravity by the centrifugal force.

The device covers part of the planet's territory.

The Intelsat system is formed by 19 satellites grouped into four regions. The subscriber sees 2-4 at the same time.

The life of the system is 10-15 years, then the obsolete equipment is changed. The gravitational effects of the planets and the Sun reveal the need to use stabilization systems. The correction process significantly reduces the fuel resource of the vehicles. The Intelsat complex allows position deviations of up to 3 degrees, extending the life of the orbital swarm (over three years).

Frequencies

The transparency window is limited to the 2-10 GHz range. Intelsat uses the 4-6 GHz region (C-band). The increase in load caused the transition of part of the traffic to the Ku-band (14, 11, 12 GHz). The working area is distributed in portions to transponders. The terrestrial signal is received, amplified, radiated back.

Problems

1. The high cost of launching. Overcoming 35 thousand kilometers takes a lot of resources.
2. The signal propagation delay exceeds a quarter of a second (reaching 1 s).
3. A small angle of inclination of the line of sight of an artificial aircraft increases energy costs.
4. The reception area is covered ineffectively. Giant spaces are devoid of subscribers. Broadcast efficiency is extremely low.
5. The transparency windows are narrow, ground stations have to be scattered geographically, to change polarization.

Solutions

The introduction of an inclined orbit partially eliminates the disadvantages. The satellite ceases to be geostationary (see above Cold War spy satellites). At least three equidistant devices are required to ensure communication around the clock.

Polar orbit

The polar orbit alone is capable of covering the surface. However, several orbital periods of the spacecraft will be required. A swarm of satellites, spaced around the corner, is able to solve the problem. Polar orbits have bypassed commercial broadcasting, becoming a faithful assistant to the systems:

• navigation;
• meteorology;
• ground control stations.

Inclined orbit

The tilt was successfully used by Soviet satellites. The orbit is characterized by the following parameters:

• circulation period - 12 hours;
• tilt - 63 degrees.

Visible for 8/12 hours, three satellites provide communication to polar regions inaccessible from the equator.

Satellite phone

The mobile gadget directly catches space, bypassing ground towers. The first Inmarsat of 1982 provided access for seafarers. A terrestrial species was created seven years later. Canada was the first to recognize the benefits of equipping desert areas with rare inhabitants. Following the program, the United States mastered.

The problem is solved by launching low-flying satellites:

1. The circulation period is 70..100 minutes.
2. Height 640..1120 km.
3. The coverage area is a circle with a radius of 2800 km.

Taking into account the physical parameters, the duration of an individual communication session covers the range of 4-15 minutes. Maintaining performance requires a certain amount of effort. A couple of US merchants went bankrupt in the 90s, unable to gain enough subscribers.

Weight and dimensions are continuously improving. Globalstar offers proprietary smartphone software that uses Bluetooth to catch the signal of a relatively bulky satellite receiver.

Satellite phones require a powerful receiving antenna, preferably fixed. They mainly equip buildings and transport.

Operators

1. ACeS covers Asia with a single satellite.
2. Inmarsat oldest operator (1979). Equips yachts, ships. With 11 aircraft, the company is slowly expanding into the mobile market with the help of ACeS.
3. Thuraya serves Asia, Australia, Europe, Africa, the Middle East.
4. MSAT / SkyTerra is an American provider using equipment equivalent to Inmarsat.
5. Terrestar covers North America.
6. IDO Global Communications is inactive.

Networks

Commercial projects are limited.

GlobalStar

GlobalStar is a joint brainchild of Qualcomm and Loral Corporation, later backed by Alcatel, Vodafone, Hyundai, AirTouch, Deutsche Aerospace. The launch of 12 satellites was disrupted, the first call took place on November 1, 1998. The initial cost (Feb 2000) was $ 1.79 / min. After going through a series of bankruptcies and transformations, the company provides clients in 120 countries.

Provides 50% of US traffic (over 10,000 calls). Operation is supported by terrestrial repeaters. 40 in total, including 7 accommodated by North America. Territories devoid of terrestrial repeaters form a zone of silence (South Asia, Africa). Although the devices regularly ply the heavenly heights.

Subscribers receive American phone numbers, excluding Brazil, where they assign the code +8818.

List of services:

• Voice calls.
• Positioning systems with an error of 30 km.
• 9.6 kbps Internet packet access.
• Mobile communication CSD GSM.
• Roaming.

The phones use Qualcomm CDMA technology, excluding Ericsson and Telit, which accept traditional SIM cards. Base stations are forced to support both standards.

Iridium

The provider uses polar orbit, providing 100% coverage of the planet. The organizers went bankrupt, and the company was revived in 2001.

It is interesting! Iridium is the culprit behind nighttime sky flares. Flying satellites are clearly visible to the naked eye.

The company's fleet includes 66 satellites using 6 low-earth orbit trajectories with an altitude of 780 km. The devices communicate using the Ka-band. The lion's share was run by former bankruptcy companies. As of January 2017, 7 units have been updated. Regeneration continues: the first group (10 pieces) flew away on January 14, the second on June 25, and the third on October 9.

It is interesting! Satellite Iridium 33 on February 10, 2009 rammed Russian Space 2251. Heavenly debris is flying over Siberia today.

The company continues to provide services to 850 thousand subscribers. 23% of the profit was paid by the state. The cost of the call is 0.75 - 1.5 USD / min. Callbacks are comparatively expensive at $ 4 / min (Google Voice). Typical areas of employment for employers:

1. Oil production.
2. Marine fleet.
3. Aviation.
4. Travelers.
5. Scientists.

Inhabitants of the Amundsen-Scott South Polar Station asked to give special thanks. The company sells call packages with a duration of 50-5000 minutes everywhere. The validity of the former leaves much to be desired, expensive ones (5000 minutes = 4000 dollars) remain operational for 2 years. Monthly renewal - $ 45:

• 75 minutes cost $ 175 and can be used for 1 month.
• 500 minutes - $ 600-700, period of use - 1 year.

Telephones

The former owners supplied their customers with telephone sets from two manufacturers:

Motorola 9500 became a companion of the first commercial trial of the company. The mobile shock-resistant version 9575, which exists today, was born in 2011, supplemented by an emergency GSM call button, an advanced location interface. The device sets up a Wi-Fi hotspot, allowing users of ordinary smartphones to send emails, SMS, and browse the Internet.

Kyocera equipment has been abandoned by the manufacturer. Models are sold by dealers. The KI-G100 based on a 900 MHz GSM phone is equipped with a suitcase equipped with a powerful antenna that picks up the broadcast. The ability to receive SMS is provided, only certain models can be poisoned (9522). The SS-66K is equipped with an atypical ball antenna.

1. The 9575 is a shockproof, waterproof phone with a dustproof casing. Withstands temperatures from minus 20 to plus 50 degrees Celsius.
2. 9555 - equipped with a built-in headset, USB interface, an adapter to a serial RS-232 port.
3. The 9505A is a hefty brick-shaped gadget. Equipped with native RS-232 interface.
4. SS-55K is a limited edition. Incredible size, sold by eBay resellers.

Other company equipment included:

1. Pagers.
2. Payphones.
3. Equipment for yachts, airplanes.

Buoys

Floating buoys resembling a tsunami tracking system are capable of receiving / transmitting short messages. The interface will allow you to use the functionality of a branded phone that refuses to catch satellites.

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

For the first time the idea of ​​satellite communications was presented in 1945 by the Englishman Arthur Clarke. 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 stationary over a certain place and within the optical visibility range from almost half of the earth's surface. Three repeaters, placed in a properly selected orbit with an angular separation of 120 °, will be able to cover the entire planet with television and VHF broadcasting; I am afraid that those who are planning post-war work will not find it easy, but I consider this path 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 the pilot-cosmonaut Yu. A. Gagarin on board was launched into the orbit of the Earth satellite. To measure the parameters of the orbit of the satellite spacecraft and control the operation of its onboard equipment, numerous measuring and radiotelemetric equipment was installed on it. For direction finding of the spacecraft and transmission of telemetric information, the Signal radio system operating at a frequency of 19.955 MHz was used. The cosmonaut's two-way communication with the Earth was provided by a radiotelephone system operating in the short (19.019 and 20.006 MHz) and ultrashort (143.625 MHz) wave bands. 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 a full-face image of the pilot, and the other - from the side.

Achievements of domestic science in the field of space exploration made it possible to implement the predictions of Arthur Clarke. At the end of the 50s of the last century, experimental studies of the possibilities of using artificial earth satellites as radio repeaters (active and passive) in terrestrial communication systems began to be carried out in the USSR and the USA. Theoretical developments in the field of energy capabilities of satellite communication lines made it possible to formulate the tactical and technical requirements for satellite repeater devices and ground devices, based on the real characteristics of the technical means that existed at that time.

Considering 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 relay "Score" was launched on December 18, 1958 into an inclined elliptical orbit with an apogee altitude of 1481 km, a perigee of 177 km. The satellite equipment consisted of two transceivers operating at frequencies 132.435 and 132.095 MHz. The work was carried out in slow retransmission mode. The storage of the signal sent by the ground transmitting station was carried out by recording it on a magnetic tape. Silver-zinc batteries with a capacity of 45 amperes - an hour at a voltage of 18 volts were used as power sources. The duration of the connection was approximately 4 minutes per 1 satellite revolution. Retransmission of 1 telephone or 7 teletype channels was carried out. The satellite's service life was 34 days. The satellite burned up upon entering the atmosphere 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 (150 MHz for command transmission and 1900 MHz for communication), magnetic memory devices and power sources - solar cells and chemical batteries. Silicon solar cells in the amount of 19,152 were used as the primary power source. Nickel-cadmium batteries with a capacity of 10 ampere-hour at a voltage of 28-32 volts were used as a buffer stage. The duration of the communication session was 5 minutes per revolution of the satellite. The satellite service life was 1 year. On July 10, 1962, an active Telstar repeater 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, he rebroadcast either 600 simplex telephone channels, or 12 duplex telephone channels, or one television channel. In all cases, the work was carried out using the frequency modulation method. Communication frequencies: on the satellite-Earth line 4169.72 MHz, on the Earth-satellite line 6389.58 MHz. The duration of a communication session on the US-Europe line via this satellite was about 2 hours a day. The quality of the transmitted television images ranged from good to excellent. The project envisaged a very significant service life of the satellite - 2 years, but after four months of successful operation, the command line failed. It was found that the causal failure was surface damage due to the action of radiation when the satellite passed the inner radiation belt.

On February 14, 1963, the first synchronous satellite of the Sinkom system was launched with orbital parameters: apogee altitude 37,022 km, perigee altitude 34185, orbital period 1426.6 minutes. The operating frequency on the Earth-to-satellite link is 7360 MHz, and on the satellite-to-Earth link, 1820 MHz. Solar cells in the amount of 3,840 units 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 the observations were carried out by astronomical methods.

On April 23, 1965, the first communications satellite, Molniya-1, was launched in the USSR. With the launch of the second communications satellite "Molniya-2" on October 14, 1965, the regular operation of the long-distance communication line through the satellite began. Later, the Orbita long-range space communications system was created. It consisted of a network of ground stations and artificial earth satellites "Molniya", "Raduga", "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 Ussuriisk. They were connected by cable and relay communication lines, respectively, with television centers and telephone intercity stations in Moscow and Vladivostok.

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

Specially developed transmitters for communication and command and measurement 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, the designers of the earth station, fearing the influence of powerful transmitters on the 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 to transfer the receiving equipment to the transmitting antenna in the future, which greatly simplified and reduced the cost of operating satellite communication stations.

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

However, the Molniya satellites revolved around the Earth in elongated elliptical orbits. To track them, the antennas of the 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 terrestrial observer hanging motionless over one point of our planet. Three such satellites are enough to provide communications for the entire Earth.

In the 80s of the last century, communication satellites "Raduga" and television satellites "Ekran" effectively operated in stationary orbits. No sophisticated ground stations were needed to receive their signals. 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, the satellite phone is directly connected to the satellite in low-earth orbit. From the satellite, the signal enters the ground station, from where it is transmitted to the regular telephone network. The number of satellites required for stable communication anywhere on the planet depends on the orbital radius of a particular satellite system.

The main disadvantage of personal satellite communication is its relative high cost compared to cellular communication. 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, which was established over 20 years ago. The satellite phones of the Inmarsat system are hinged cases the size of the first laptop computers. The satellite phone cover is also an antenna, which must be turned towards the satellite (the signal strength is displayed on the phone display). These phones are mainly used on ships, trains or heavy vehicles. Every time, when 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.

At present, satellite systems still account for about 3% of world traffic in the overall balance of communications. But the demand for satellite links continues to grow, since with a range of more than 800 km, satellite channels become more cost-effective compared to other types of long-distance communications.