|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Cellular. History of invention and production
Directory / The history of technology, technology, objects around us Cellular communication, a mobile communication network is one of the types of mobile radio communication, which is based on a cellular network. The key feature is that the total coverage area is divided into cells (cells) determined by the coverage areas of individual base stations (BS). The cells partially overlap and together form a network. On an ideal (flat and undeveloped) surface, the coverage area of one BS is a circle, so the network composed of them looks like hexagonal cells (honeycombs). The network consists of spatially separated transceivers operating in the same frequency range, and switching equipment that allows you to determine the current location of mobile subscribers and ensure communication continuity when a subscriber moves from the coverage area of one transceiver to the coverage area of another. The mobile network includes a large number of base stations, the service areas of which are partially overlapped due to their limited transmitting power. Thus, the area in which the connection of a mobile phone with the considered base station is theoretically guaranteed, in terms of the plan, is a polyhedron - a cell resembling a honeycomb. It is from here that this type of mobile radio communication got its name - cellular.
It turns out that the question of how old the phone is is not so easy to answer. Judge for yourself: the principle of transforming the vibration of the membrane from sound waves into an electrical signal, which is to be further transmitted over wires over a distance, was discovered by the French researcher Charles Boursol in 1854. Later, the German naturalist Johann Reis learned how to transmit musical sounds through wires. But it was not possible to convey the speech. Finally, in 1876, luck smiled at the American inventor Alexander Bell, who guessed that direct current was needed to transmit speech, and developed a primitive (but working) telephone. It looked terrible: in the center of the "still life" was a horseshoe-shaped magnet with a wire wound around it - no aesthetics. Let's make a reservation that Bell's priority is the American version of history, but some researchers dispute it, finding a "Russian trace" in the invention. However, it was Bell who patented the technology, and we owe the word "telephone" to him. Since then, the phone began to rapidly change both externally and internally. In the 1920s it was a "bell" with a detachable loudspeaker. In 1937, the telephone acquired the now familiar handset and a rotating dial for dialing. And he lived in this form in the USSR and in the countries of Eastern Europe until the end of the 1980s. The Soviet industry has never produced cordless telephones. Mobility within the limits of one's own apartment was solved by installing a long, more than ten meters, twisted cord, which made it possible to carry the phone into the next room. In the early 1990s, cordless touch-tone telephones appeared. Gradually, home and office devices operating in the 50 MHz band with a range of several tens of meters were replaced by 900 MHz devices. The latter provided higher noise immunity, some protection from twin devices and a range of up to several hundred meters from the base station. The actual range was highly dependent on the type of room, the number of concrete bulkheads and other obstacles. However, modern 900-MHz devices allow you to work comfortably in a large office and multi-storey building. In fact, the ancestors of cellular mobile communications were radiotelephone extension cords and various autonomous radio networks. By the way, the Altai radial-zonal special communications network, widely known back in Soviet times, which was used by the then state elite, provided mobility within hundreds of impressive sizes. Since this network had few subscribers, there was no question of saving the radio frequency resource at that time. Similar communication systems were available in other countries, but this was only a prelude to the future of cellular communications. The introduction of true cellular networks began only after the problem of saving the radio frequency spectrum was solved and ways were found to determine the current location of mobile subscribers. This was necessary for optimal routing of calls to them and ensuring continuity of communication when a subscriber moves from one cell to another. The birth of cellular communication dates back to 1971. It was then that the Bell System company submitted to the US Federal Communications Commission (FCC) a description of the architecture of radiotelephone communications, which later became known as cellular. But the path from an idea to a real project took quite a long time - commercial cellular networks started working only ten years later. The development of cellular systems in the 1970s and their subsequent implementation in the 1980s presented a variety of challenging technical problems. One of the most serious was the creation of portable subscriber terminals, small in size and weight. At the turn of the 1970s, even advanced technical solutions for car terminals weighed a little less than 15 kilograms. And the device of the same purpose had to be implemented in sizes and weights acceptable for holding with one hand near the ear. The specialists of Motorola (USA) managed to show off the first successes. One of the founders of new areas of telecommunications is Martin Cooper, who in the early 1970s served as vice president of Motorola. He was the first to propose ways to radically reduce the size of the radiotelephone. And in 1973, the first relatively small radiotelephone appeared, which successfully passed laboratory tests. Martin Cooper made the first call with him to a fellow competitor from Bell Laboratories. As Cooper himself testifies, he uttered the following words: "Imagine, Joel, that I call you from the world's first cell phone. I have it in my hands, and I'm walking along a New York street."
In the mid-1980s, Martin Cooper's name was inducted into the Wireless Hall of Fame. The first cellular communication systems were analog and had one serious drawback - the incompatibility of systems from different manufacturers. This significantly limited the ability to move subscribers between countries and even cities where different types of systems were deployed. Analogue cellular networks so familiar to the modern user began to be created in the early 1980s in many European countries on the basis of unified equipment of the MMT-450 standard and in the USA on the basis of the AMPS standard. It was they who at that time were destined to take over the bulk of the mobile subscribers around the world. As a result of a European initiative in 1982, a group of GSM mobile communications experts (Group Special Mobile) of 17 European communications administrations arose, which began to develop a new digital standard for cellular communications. Many years of GSM efforts have been successful, and today we have another widely used decoding of the GSM abbreviation. Global System for Mobile Communications (Global System for Mobile Communications). To solve the problems of implementation and operation of the new standard in 1987, the European working group MoU was founded - a memorandum of understanding of the essence of joint agreements on use. This community of partners currently includes more than one hundred operators from almost 100 countries around the world. The serious approach of Europeans to the creation of a new standard led to success - the emergence of the current leader of European cellular communications - the GSM standard, operating in the 900 MHz band. “In 1988, the main documents were adopted and the development of the production of equipment for service systems of this standard began,” A. Golyshev writes in the Radio magazine. “And in 1991, the first GSM networks were already practically used. can be considered an example of a joint solution of complex technical and organizational problems by a large group of countries.The system and technical solutions developed within the framework of GSM are currently widely used in the creation of promising digital cellular communication systems, including those based on other technologies. solutions include the construction of GSM networks on the principles of intelligent networks, the use of an open systems model, the introduction of new efficient models of frequency reuse, etc." The standard uses time division multiple access (TDMA), operating in the frequency range 890...915 MHz (uplink) and 935...960 MHz (downlink) with a channel bandwidth of 200 kHz . In addition to traffic channels, there are also control channels. Thus, eight logical communication channels are implemented in one physical radio channel in GSM, each of which can be used by a separate subscriber. One base station can support a maximum of 16-20 radio channels. The maximum data transfer rate in the system is 9,6 Kbps. The GSM standard uses the so-called spectrally efficient Gaussian frequency shift keying with a minimum frequency shift. To protect against errors in the radio channels of the GSM system, convolutional and block coding with interleaving is used. Convolutional coding deals with single errors, interleaving allows group errors to be converted to single ones, and block coding gets rid of the remaining uncorrected errors. An increase in the efficiency of coding and interleaving at a low speed of movement of subscriber terminals is achieved by slow switching of operating frequencies during a communication session at a rate of 217 hops per second. For a high degree of security of message transmission, they are additionally encrypted using a public key algorithm. "The functional composition of the system is quite traditional, - notes A. Golyshev, - it consists of a switching center, a control and maintenance center, base stations and subscriber terminals. The switching center serves a group of cells (cells), each of which contains a base station (separate groups of base stations are controlled by a specialized controller), providing all types of connections that a subscriber mobile station needs, as well as "handover" when a subscriber moves (from a cell cell) and switching radio channels when interference or malfunctions occur. The switching center continuously monitors the location of mobile stations, storing this information in special secure databases. This allows servicing (roaming) of users of other networks of this standard (owned by other operators) ... ...The developers have made sure that the GSM system has its own internal mechanism for determining the location of subscribers and routing calls, independent of the specific telephone network to which it is connected, and, accordingly, could simply do the same in any part of each country. All this facilitates the organization of automatic roaming, which is now widely used throughout the world." To exclude unauthorized access to the GSM network, the subscriber is authenticated. At the same time, everyone receives a standard subscriber authentication module for the duration of using the network, which contains an international identification number, its own individual key and authentication algorithm. Having inserted his card into the terminal, the subscriber turns the latter into his individual device. To provide additional protection for his terminal, the subscriber can set such an operating mode in which it is necessary to additionally type a pin code on the keyboard. Another important node in the GSM network responsible for its reliability is the operation and maintenance center (OMC). It provides control and management of all network components, and also controls the quality of its work. Depending on the nature of the fault, the OMC allows it to be corrected automatically or with the help of emergency intervention by technical personnel. The GSM network has a control center dedicated to the operation and maintenance of the entire network, which may contain several regional OMCs. The system provides its subscribers with a wide range of call transfer services, notification of tariff costs, inclusion in a closed user group. The use of various equipment in the network allows, in addition to voice communication, to transmit data, short messages, emergency signals, including emergency information, apartment security signals, and distress. Author: Musskiy S.A.
▪ Diskette
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Origami helps generate electricity ▪ Climate change causes bees to deform
▪ section of the Garland website. Article selection ▪ article by Ernst Junger. Famous aphorisms ▪ article What are the rings of Saturn? Detailed answer ▪ Passionflower article. Legends, cultivation, methods of application ▪ article Paints, drying oils. Simple recipes and tips
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page