Cellular ( mobile connection) - one of the types of mobile radio communications, which is based on a cellular network. This is a more modern development. telephone connection for this day. main feature consists in the fact that the total coverage area is divided into cells (cells) determined by the coverage areas of individual base stations (BS). Cells partially overlap and together form a network. On an impeccable (flat and in the absence of buildings) surface, the coverage area of one BS is a circle, therefore the network composed of them looks like honeycombs with hexagonal cells (honeycombs).
The benefits of cellular communication are clear: a mobile phone gives freedom of movement throughout the network service area, each subscriber can choose a more suitable service tariff. Apart from telephone services, cellular offers Additional services: this is both voicemail and forwarding, SMS, MMS, EMS, GPRS, EDGE, 3G etc. (depending on the mobile phone model).
The cellular network consists of transceivers spaced apart in space operating in the same frequency spectrum, and switching equipment that allows you to determine the current position of mobile subscribers and ensure communication continuity when a subscriber moves from the coverage area of the 1st transceiver to the coverage area of another.
The principle of operation of cellular communication
Main Ingredients cellular network are mobile phones and base stations. Base stations are usually located on the roofs of buildings and towers. When turned on, the mobile phone listens to the air, finding the signal of the base station. The phone then sends its own unique identification code to the station. The telephone and the station maintain constant radio contact, occasionally exchanging packets. The phone can communicate with the station using an analog protocol ( AMPS, NAMPS,NMT-450) or by digital ( DAMPS, CDMA, GSM, UMTS). In that case, the phone leaves the field of action of the base station, it establishes communication with another (eng. handover).
Cellular networks can consist of base stations of various standards, which improves network performance and improves its coverage.
The cellular networks of various operators are connected together, also to the fixed telephone network. This allows subscribers of the 1st operator to make calls to subscribers of another operator, from mobile phones to landlines and from landlines to mobiles.
Operators can conclude roaming agreements among themselves. Thanks to such agreements, the subscriber, being outside the coverage area of his own network, can make and receive calls through the network of another operator. Most often, this is carried out at inflated rates.
It is hardly possible today to find a person who would never use a cell phone. But does everyone understand how cellular communication works? How is it arranged and how does what we all have long been accustomed to work? Are signals from base stations transmitted over wires, or does it all work in some other way? Or maybe all cellular communication functions only due to radio waves? We will try to answer these and other questions in our article, leaving a description GSM standard outside of it.
At the moment when a person tries to make a call from his mobile phone, or when they start calling him, the phone connects via radio waves to one of the base stations (the most accessible), to one of its antennas. Base stations can be observed here and there, looking at the houses of our cities, at the roofs and facades of industrial buildings, at skyscrapers, and finally at red-white masts specially erected for stations (especially along highways).
These stations look like rectangular gray boxes, from which various antennas stick out in different directions (usually up to 12 antennas). The antennas here work both for reception and for transmission, and they belong to the mobile operator. Antennas base station sent to all possible directions (sectors) to provide “network coverage” to subscribers from all sides at a distance of up to 35 kilometers.
An antenna of one sector is able to serve up to 72 calls simultaneously, and if there are 12 antennas, then imagine: 864 calls can, in principle, be served by one large base station at the same time! Although usually limited to 432 channels (72 * 6). Each antenna is connected by cable to the control unit of the base station. And already blocks of several base stations (each station serves its own part of the territory) are attached to the controller. Up to 15 base stations can be connected to one controller.
The base station, in principle, is capable of operating on three bands: the 900 MHz signal penetrates better into buildings and structures, spreads further, so this particular band is often used in villages and fields; the signal at a frequency of 1800 MHz does not spread so far, but more transmitters are installed in one sector, so such stations are more often installed in cities; finally 2100 MHz is a 3G network.
Of course, there may be several controllers in a settlement or district, so the controllers, in turn, are connected by cables to the switch. The task of the switch is to connect the networks of mobile operators with each other and with city lines of regular telephone communication, long-distance communication and international communication. If the network is small, then one switch is enough; if it is large, two or more switches are used. The switches are interconnected by wires.
In the process of moving a person talking on a mobile phone along the street, for example: he walks, rides in public transport, or moves in a personal car, his phone should not lose the network for a moment, you cannot cut off the conversation.
Communication continuity is obtained due to the ability of the base station network to very quickly switch the subscriber from one antenna to another in the process of moving from the coverage area of one antenna to the coverage area of another (from cell to cell). The subscriber himself does not notice how he ceases to be connected with one base station, and is already connected to another, how he switches from antenna to antenna, from station to station, from controller to controller ...
At the same time, the switch provides optimal load distribution over a multi-layer network scheme in order to reduce the likelihood of equipment failure. A multilevel network is built like this: cell phone - base station - controller - switch.
Let's say we make a call, and now the signal has already reached the switch. The switch transfers our call towards the destination subscriber - to the city network, to the international or long-distance communication network, or to the network of another mobile operator. All this happens very quickly using high-speed fiber optic cable channels.
Further, our call arrives at the switchboard, which is located on the side of the receiving call (called by us) subscriber. The "receiving" switch already has data about where the called subscriber is located, in what network coverage area: which controller, which base station. And so, the network polling begins from the base station, the addressee is found, and a call “receives” on his phone.
The entire chain of the described events, from the moment of dialing the number to the moment the call is heard on the receiving side, usually lasts no more than 3 seconds. So we can now call anywhere in the world.
Andrey Povny
It is difficult to imagine today a person who does without cellular communication. Every day people call each other, send millions of messages, go online using mobile phones. Cellular operators are responsible for the quality of communication, cost and package of services.
List of telecom operators in Russia
There is no single operator responsible for mobile communications. There are more than a hundred active mobile operators in Russia. Some regional providers are subsidiaries of large mobile operators Russia.
According to statistics, among the leaders among companies providing mobile communication services are 3 - the "big three" providers - MTS, Megafon, Beeline. These companies have the largest number of subscribers, the largest coverage area, and a wide range of services.
- MTS. The only "cell phone", which is included in the top 20 world leaders. According to the results of 2017, it has the largest number of subscribers in Russia (more than 78 million people), and taking into account the CIS countries, the number of subscribers is more than 100 million. It has the most extensive network of communication salons in the country (more than 5700 points).
- Megaphone. There are more than 76 million subscribers in Russia, there is a great demand for Megafon SIM cards in Abkhazia, Tajikistan, and South Ossetia. The company positions itself as the operator with the fastest mobile Internet.
- Beeline. The VimpelCom brand is included in the top 100 recognizable brands in the world. The number of subscribers in Russia reaches 59 million people, but Beeline is the leader in terms of the number of roaming countries and partners. This allows you to stay connected while traveling and save on roaming services.
The top popular operators include companies that are not included in the 3 "big three", but in terms of popularity they are a significant competitor. The rating of mobile operators includes both smaller companies, new ones, and regional ones. The very concept of the “big three” is becoming obsolete, because Other providers are also gaining market share:
- Tele2. At the end of 2017, it is the only company that has increased the number of subscribers. As a federal Russian operator, it has been operating since 2014 after obtaining a license for communication in 3G format. The operator's audience is at least 40 million people in 65 regions of the country. Most active subscribers are in Moscow and the Moscow region, St. Petersburg, Chelyabinsk and Nizhny Novgorod regions. It ranks 3rd in Russia in terms of the number of base stations, is distinguished by fast mobile Internet due to low network load, as well as affordable package tariffs with internet.
- Yota is a virtual cellular operator. The brand has been in existence since 2008. Works on the technical infrastructure of MegaFon. The subscriber base is about 1.5 million people. Until January 2017, the only operator with unlimited access to mobile Internet, today tariff line includes only data-limited products for smartphones, while there are offers for tablets and computers with unlimited internet, the price of which depends on the speed.
- Rostelecom is an Internet provider and a company providing home wired communication and cable television services. The company offers its subscribers cellular communication in GSM 900/1800 format and mobile Internet.
- "Motive" serves only 4 regions in the Urals Federal District. This brand has been in existence since 2002. The company provides communication in GPRS / EDGE, IVR, MMS, SMS, USSD formats, it is not represented in Moscow.
- "SMARTS" is a Samara company. Communication in Russia is provided to subscribers from the Volga region and the central regions of the country. The list of services includes data transfer GPRS, CSD, communication in the standards GSM-900, GSM-1800, SMS, MMS.
Before making a choice of a mobile operator, each client must outline their own circle of preferences and identify requirements for mobile communications. Each provider is good in its own way, best operator cellular communication can also be of regional status, if the package of services that it provides meets the needs of the client.
A list for communication in Russia, a phone code and a comparison of operators will help you choose the right provider.
Map of mobile operators
Communications companies are sensitive to increasing customer requirements. Now not only major players in the telecommunications market offer high-quality communication coverage. The appearance of new towers makes it possible to provide communication even to the most remote settlements, you can now use a mobile phone in the subway and in skyscrapers. Operators provide not only high-quality and uninterrupted telephone coverage, but also fast access to the Internet via 3G and 4G networks.
Each company is struggling to retain existing subscribers and expand its consumer base, therefore, in almost every city there are salons where customers can not only purchase a starter package, but also receive qualified assistance or answers to their questions.
Each Russian company there is a database of 11-digit numbers by which you can determine the operator and regions of connection of the number. The possibility of switching from one operator to another, which appeared after the abolition of "mobile slavery", was not used by all subscribers, so the code table helps to determine where the unknown incoming "came from".
If the number is registered in Moscow and the Moscow region, then the unknown number incoming call easy to define:
Beeline does not have a clear link to the region, like other major operators. Separate codes the company has installed only for Far East and Primorsky Krai. And Yota numbers are not tied to the region, they all start with the code 999.
By Northwest region and St. Petersburg
Southern federal district, including the North Caucasus
The tables show both codes calculated for all regions, and those that apply only in the specified city, district. But large operators have codes for certain areas, that is, cellular services will be cheaper only when using them in the home region.
The place of registration of numbers with codes 950, 951, 952 at Tele2 can be the Irkutsk Region, Khanty-Mansiysk Region, Lipetsk Region, Kursk Region, Perm Territory, Chelyabinsk Region, Kemerovo Region, Republic of Buryatia, Republic of Mordovia, Tyumen Region and Udmurtia.
Large operators have allocated separate codes for the Urals: 922 - Megafon, 982 - MTS.
What numbers do Russian operators use
The phone number of any Russian operator starts with 8, for dialing in international format you need to dial +7. However, within Russia, the call will be equally successful when dialing both from the eight and from +7.
After the international code, the prefix digits follow - this is the DEF code used in mobile networks. The prefixes of Russian operators start with 9, i.e. the general form of the code is always this: 9xx. For companies providing mobile communication services, one or more of these codes are allocated. This makes it possible to determine the operator and the region of the caller: 926, 916, 977 are Moscow numbers, and 911, 921 or 981 are St. Petersburg numbers.
For the "mobile trio" a series of codes are allocated, in which the second digits also coincide. For example, 91x or 98x are MTS numbers, and 92x or 93x are Megaphone numbers.
The next 7 digits are the subscriber's number, by which it is impossible to determine belonging to the region of residence or provider. The range of Beeline numbers can suggest belonging to the region if the same prefix is used. Code 905 is used in St. Petersburg (range from 250-00-00 to 289-99-99), as well as in the Ulyanovsk region. (range from 183-00-00 to 184-99-99).
But sometimes only the initial digits of the subscriber's number help to determine the operator. For example, DEF-code 958 is used by more than 20 operators, among which there are both small companies (with coverage of 1 region and a capacity of 10,000 numbers) and large ones (several tens of regions and hundreds of thousands of numbers).
As an example: the prefix of the numbers of the TransTelecom company is 7958, but since the company serves 30 regions of the country, you need to know the initial digits of the subscriber's number in order to determine the ownership of the outgoing call (-00x-xx-xx - Bashkiria, and -03x-xx-xx - Kaliningrad region, etc.).
The same prefix is used by Gazprom Telecom, Delovaya Set Irkutsk, Smolny Automatic Telephone Station, Interregional TransitTelecom, Systematics, T2 Mobile, Central Telegraph, etc.
The numbering of DEF codes also changes as needed. Moscow MTS numbers were transferred from 495 to 985, and Megafon numbers from 495 to 925.
The telephone code that only Megafon uses is 920. The number capacity is more than 10 million, and numbers with this code are used in 17 regions of the Russian Federation.
The encoding used by Tele2 is 900. But the same code is used by 16 other Russian operators of various sizes in terms of capacity and coverage of regions - Antares, Arkhangelsk Mobile Networks, Ekaterinburg-2000, Kemerovo Mobile Communications, Sky- 1800" and others.
Tele2 is the largest of the companies using the 900 prefix: T2 Mobile is 17 regions and 3,140,000 numbers (the region is determined by the digits of the subscriber number), Tele2-Omsk is 3 regions (Jewish Autonomous Region, Omsk Region and Chukotka Autonomous Okrug) and 210,000 numbers, Tele2-St. Petersburg - 1 million numbers for 4 regions (Vologda region, Karelia, Pskov region, Leningrad region and St. Petersburg).
Best Rates
The ratings of companies providing cellular services are compiled not only taking into account the number of subscribers and the extent of the coverage area, but also the list of services provided by the company and the tariffs set for each position or the entire package.
The advertising campaigns of the four leading providers (MTS, Megafon, Tele2, Beeline) are aimed at attracting subscribers, therefore TV commercials vied with each other to prove that the tariffs of one or another company are the most favorable. Telecom operators' tariffs dynamically reflect the company's strategy, consumer preferences and industry trends. At the same time, archival tariffs also operate in parallel until the subscriber switches to a new price offer.
Budget tariffs
| MTS, SmartMini | Megaphone, "All inclusive XS" |
beeline, "All for 300" |
Tele 2, "My Conversation" |
|
| Cost, rub.) | 250 | 250 | 300 | 240 |
| Minutes package | 250 | 200 | 350 | 150 |
| Internet (GB) | 1 | 2 | 15 | 2 |
In such a variety it is not difficult to get lost, but there is no universal tariff plan. It is more convenient and cheaper for subscribers to purchase a range of services - tariff packages that combine, for example, voice communication, SMS and mobile internet. In addition to the services included in the package, you need to study the limits on them (GB, free minutes, number of SMS) and decide on the needs of the subscriber (mobile Internet, calls to home network, roaming, etc.).
Communication is called mobile if the source of information or its recipient (or both) move in space. Radio communication has been mobile since its inception. Above, in the third chapter, it is shown that the first radio stations were intended for communication with moving objects - ships. After all, one of the first radio communication devices A.S. Popov was installed on the battleship "Admiral Apraksin". And it was thanks to radio communication with him that in the winter of 1899-1900, this ship, iced in the ice of the Baltic Sea, was saved. However, in those years, this "mobile communication" required bulky radio transceivers, which did not contribute to the development of much-needed individual radio communications even in the Armed Forces, not to mention private customers.
June 17, 1946 in St. Louis, USA, the leader of the telephone business, AT&T and Southwestern Bell, launch the first radio telephone network for private clients. element base apparatuses were tube electronic devices, so the equipment was very bulky and intended only for installation in cars. The weight of the equipment without power supplies was 40 kg. Despite this, the popularity of mobile communications began to grow rapidly. This created a new, more serious problem than weight and size indicators. An increase in the number of radio facilities, with a limited frequency resource, led to strong mutual interference for radio stations operating on channels close in frequency, which significantly worsened the quality of communication. To eliminate mutual interference at repeating frequencies, it was necessary to provide a minimum of a hundred-kilometer spacing in space between two groups of radio systems. That is why mobile communications were basically used for the needs of special services. For mass implementation, it was necessary to change not only the weight and size indicators, but also the very principle of organizing communications.
As noted above, in 1947, a transistor is invented that performs the functions of electronic tubes, but has a much smaller size. It was the appearance of transistors that was of great importance for the further development of radiotelephone communications. The replacement of electronic tubes with transistors created the prerequisites for the widespread introduction of the mobile phone. The main limiting factor was the principle of organizing communication, which would eliminate or at least reduce the effect of mutual interference.
Studies of the ultrashort-wave range of waves, carried out in the 40s of the last century, made it possible to reveal its main advantage over short waves - wide range, i.e., large frequency capacitance and the main disadvantage - strong absorption of radio waves by the propagation medium. Radio waves of this range are not able to go around the earth's surface, so the communication range was provided only on the line of sight, and depending on the transmitter power, a maximum of 40 km was provided. This shortcoming soon turned into an advantage, which gave impetus to the active mass introduction of cellular telephone communications.
In 1947 an employee American company Bell Laboratories D. Ring proposed a new idea of communication organization. It consisted in the division of space (territory) into small sections - cells (or cells) with a radius of 1–5 kilometers and in the separation of radio communications within one cell (by rational repetition of the used communication frequencies) from communication between cells. The repetition of frequencies has greatly reduced the problems of using the frequency resource. This made it possible to use the same frequencies in different cells distributed in space. In the center of each cell, it was proposed to place a base transceiver radio station, which provided radio communication within the cell with all subscribers. Cell sizes were determined by the maximum radio communication range telephone set with base station. This maximum range is called the cell radius. During a conversation, the cellular radiotelephone is connected to the base station by a radio channel over which the telephone conversation is transmitted. Each subscriber must have his own micro-radio station - "mobile phone" - a combination of telephone, transceiver and mini-computer. Subscribers communicate with each other through base stations that are connected to each other and to the city telephone network common use.
To ensure uninterrupted communication during the transition of the subscriber from one zone to another, it was necessary to use computer control over the telephone signal emitted by the subscriber. It was computer control that made it possible to switch a mobile phone from one intermediate transmitter to another within just a thousandth of a second. Everything happens so fast that the subscriber simply does not notice it. Thus, computers are the central part of the mobile communication system. They look for a subscriber located in any of the cells and connect him to the telephone network. When a subscriber moves from one cell (cell) to another, computers seem to transfer the subscriber from one base station to another and connect the subscriber of a “foreign” cellular network to their “own” network. This happens at the moment when the "foreign" subscriber is in the coverage area of the new base station. Thus, they carry out roaming (which in English means "wandering" or "vagrancy").
As noted above, the principles of modern mobile communication were an achievement already in the late 40s. However, in those days, computer technology was still at such a level that its commercial use in telephone systems was difficult. Therefore, the practical use of cellular communication became possible only after the invention of microprocessors and integrated semiconductor circuits.
The first cellular telephone, the prototype of a modern device, was designed by Martin Cooper (Motorola, USA).
In 1973 in New York, on top of a 50 story building by Motorola, under his leadership, the world's first cellular base station was installed. She could serve no more than 30 subscribers and connect them to landlines.
On April 3, 1973, Martin Cooper dialed the number of his boss and said the following words: “Imagine, Joel, that I am calling you from the world's first cell phone. I have it in my hands, and I'm walking down a New York street."
The phone from which Martin called was called Dyna-Tac. Its dimensions were 225 × 125 × 375 mm, and the weight was as little as 1.15 kg, which, however, is much less than 30 kg devices of the late forties. With the help of the device it was possible to call and receive a signal, to negotiate with the subscriber. This phone housed 12 keys, of which 10 were digital for dialing the subscriber's number, and the other two provided the start of a conversation and interrupted the call. Dyna-Tac batteries allowed for about half an hour of talk time, and it took 10 hours to charge them.
Despite the fact that the main developments were carried out in the United States, the first commercial cellular network was launched in May 1978 in Bahrain. Two cells with 20 channels in the 400 MHz band served 250 subscribers.
A little later, cellular communication began its triumphant march around the world. More and more countries have realized the benefits and convenience it can bring. However, the lack of a single international standard for the use of the frequency range, over time, led to the fact that the owner of a cell phone, moving from one state to another, could not use a mobile phone.
In order to eliminate this main shortcoming, since the end of the seventies, Sweden, Finland, Iceland, Denmark and Norway have begun joint research to develop a single standard. The result of the research was the communication standard NMT-450 (Nordic Mobile Telephone), which was intended to operate in the 450 MHz band. This standard was first used in 1981 in Saudi Arabia, and only a month later in Europe. Various variants of the NMT-450 have been fielded in Austria, Switzerland, Holland, Belgium, countries in Southeast Asia and the Middle East.
In 1983, the AMPS (Advanced Mobile) network was launched in Chicago. phone service), which was developed by Bell Laboratories. In 1985, in England, the TACS (Total Access Communications System) standard was adopted, which was a variation of the American AMPS. Two years later, due to a sharp increase in the number of subscribers, the HTACS (Enhanced TACS) standard was adopted, adding new frequencies and partially correcting the shortcomings of its predecessor. France, on the other hand, stood apart from everyone else and began using its own Radiocom-2000 standard since 1985.
The next standard was the NMT-900, which uses the frequencies of the 900 MHz band. A new version came into use in 1986. It allowed to increase the number of subscribers and improve the stability of the system.
However, all these standards are analog and belong to the first generation of cellular communication systems. They use an analog method of transmitting information using frequency (FM) or phase (FM) modulation - as in conventional radio stations. This method has a number significant shortcomings, the main of which are the possibility of listening to conversations by other subscribers and the impossibility of dealing with signal fading when the subscriber moves, as well as under the influence of the terrain and buildings. Congestion frequency bands interfered with conversations. Therefore, by the end of the 1980s, the creation of the second generation of cellular communication systems based on digital signal processing methods began.
Previously, in 1982, the European Conference of Postal and Telecommunications Administrations (CEPT), which unites 26 countries, decided to create a special group Groupe Special Mobile. Its goal was to develop a single European standard for digital cellular communication. The new communication standard was developed over eight years, and for the first time it was announced only in 1990 - then the specifications of the standard were proposed. A special group initially decided to use the 900 MHz band as a single standard first, and then, taking into account the prospects for the development of cellular communications in Europe and around the world, it was decided to allocate the 1800 MHz band for the new standard.
The new standard is called GSM - Global System for Mobile Communications. GSM 1800 MHz is also called DCS-1800 (Digital Cellular System 1800). The GSM standard is a digital standard for cellular communications. It implements time division channels (TDMA - time division multiple access, message encryption, block coding, and GMSK modulation) (Gaussian Minimum Shift Keying).
The first country to launch the GSM network is Finland, which launched this standard into commercial operation in 1992. The following year, the first DCS-1800 One-2-One network went online in the UK. From this moment begins the global spread of the GSM standard around the world.
The next step after GSM is the CDMA standard, which provides faster and more reliable communication through the use of code division channels. This standard began to emerge in the United States in 1990. In 1993 CDMA (or IS-95) began to be used in the USA in the 800 MHz frequency range. At the same time, the DCS-1800 One-2-One network began its work in England.
In general, there were many communication standards, and by the mid-nineties, most civilized countries were smoothly switching to digital specifications. If the first generation networks allowed only voice to be transmitted, then the second generation of cellular communication systems, which is also GSM, allow the provision of other non-voice services. In addition to the SMS service, the first GSM phones allowed other non-voice data to be transmitted. For this, a data transfer protocol was developed, called CSD (Circuit Switched Data - data transmission over switched lines). However, this standard had very modest characteristics - the maximum data transfer rate was only 9600 bits per second, and even then, subject to a stable connection. However, for the transmission of a fax message, such speeds were quite enough.
The rapid development of the Internet in the late 90s led to the fact that many cellular users wanted to use their handsets as modems, and the existing speeds were clearly not enough for this.
In order to somehow satisfy the need of their customers for access to the Internet, engineers invent the WAP protocol. WAP is short for Wireless Application Protocol, which translates as a wireless application access protocol. In principle, WAP can be called a simplified version of the standard Internet protocol HTTP, only adapted to the limited resources of mobile phones, such as small size display, low performance of telephone processors and low data transfer rates in mobile networks. However, this protocol did not allow viewing standard Internet pages, they must be written in the WML language, which was adapted for cell phones. As a result, although subscribers of cellular networks got access to the Internet, it turned out to be very “cut down” and of little interest. Plus, to access WAP sites, the same communication channel was used as for voice transmission, that is, while you are loading or viewing a page, the communication channel is busy, and the same money is debited from your personal account as during the conversation. As a result, quite an interesting technology was practically buried for some time and was used by subscribers of cellular networks of various operators very rarely.
Cellular equipment manufacturers urgently had to look for ways to increase the data transfer rate, and as a result, HSCSD (High-Speed Circuit Switched Data) technology was born, which provided quite acceptable speed - up to 43 kilobits per second. This technology was popular among a certain circle of users. But still, this technology has not lost the main drawback of its predecessor - the data was still transmitted over the voice channel. The developers again had to do painstaking research. The efforts of engineers were not in vain, and quite recently a technology called GPRS (General Packed Radio Services) was born - this name can be translated as a packet radio data transmission system. This technology uses the principle of channel separation for voice and data transmission. As a result, the subscriber pays not for the duration of the connection, but only for the volume of transmitted and received data. In addition, GPRS has another advantage over earlier mobile data technologies - during a GPRS connection, the phone is still able to receive calls and SMS messages. Presently modern models phones on the market when making a call, suspend the GPRS connection, which is automatically resumed after the end of the call. Such devices are classified as class B GPRS terminals. It is planned to produce class A terminals that will allow you to simultaneously download data and carry on a conversation with an interlocutor. There are also special devices that are designed only for data transmission, and they are called GPRS modems or class C terminals. Theoretically, GPRS is capable of transmitting data at a speed of 115 kilobits per second, but at the moment most telecom operators provide a communication channel that allows you to develop speed up to 48 kilobits per second. This is primarily due to the equipment of the operators themselves and, as a result, the lack of cellular phones on the market that support higher speeds.
With the advent of GPRS, the WAP protocol was again remembered, since now, through new technology, access to small WAP pages becomes many times cheaper than in the days of CSD and HSCSD. Moreover, many telecom operators provide unlimited access to WAP-network resources for a small monthly fee.
With the advent of GPRS, cellular networks have ceased to be called second-generation networks - 2G. We are currently in the 2.5G era. Non-voice services are becoming more and more in demand, there is a merger of the cell phone, computer and the Internet. Developers and operators offer us more and more various additional services.
So, using the capabilities of GPRS, was created new format messaging, which was called MMS (Multimedia Messaging Service - Multimedia Messaging Service), which, unlike SMS, allows you to send from a cell phone not only text, but also various multimedia information, such as sound recordings, photos and even video clips. Moreover, an MMS message can be sent both to another phone that supports this format, and to an e-mail box.
Increasing the power of phone processors now allows you to download and run on it various programs. For their writing, the Java2ME language is most often used. It is now easy for owners of most modern phones to connect to the Java2ME application developers site and download to their phone, for example, new game or another necessary program. Also, no one will be surprised by the ability to connect the phone to a personal computer in order to save or edit on a PC using special software, most often supplied with the handset. address book or organizer; while on the road, using a bunch of mobile phone + laptop, go to full Internet and view your email. However, our needs are constantly growing, the volume of transmitted information is growing almost daily. And more and more requirements are being put forward to cell phones, as a result of which the resources of current technologies are not enough to meet our growing demands.
It is precisely for the solution of these requests that the fairly recently created third-generation 3G networks are designed, in which data transmission dominates voice services. 3G is not a communication standard, but a general name for all high-speed cellular networks that will grow and are already growing from the current ones. Huge data transfer speeds allow you to transfer high-quality video images directly to your phone, to maintain a constant connection to the Internet and local networks. The use of new, improved, security systems allows today to use the phone for various financial transactions - a mobile phone is quite capable of replacing a credit card.
It is quite natural that third-generation networks will not become the final stage in the development of cellular communications - as they say, progress is inexorable. The ongoing integration of various types of communications (cellular, satellite, television, etc.), the emergence of hybrid devices, including a cell phone, PDA, video camera, will certainly lead to the emergence of 4G, 5G networks. And today even science fiction writers will hardly be able to tell how this evolutionary development will end.
At the world level, about 2 billion units of mobile phones are now used, of which more than two-thirds are connected to the GSM standard. The second most popular is CDMA, while the rest represent specific standards used mainly in Asia. Now in developed countries there is a situation of "satiation", when demand stops growing.
Communication is called mobile if the source of information or its recipient (or both) move in space. Radio communication has been mobile since its inception. The first radio stations were designed to communicate with moving objects - ships. After all, one of the first radio communication devices A.S. Popov was installed on the battleship "Admiral Apraksin". And it was thanks to radio communications with him that it was possible in the winter of 1899-1900. save this ship, frozen in the ice in the Baltic Sea.
For many years, individual radio communication between two subscribers required its own separate radio communication channel operating at the same frequency. Simultaneous radio communication over many channels could be provided by allocating a certain frequency band to each channel. But frequencies are also needed for radio broadcasting, television, radar, radio navigation, and military needs. Therefore, the number of radio channels was very limited. It was used for military purposes, government communications. So, in cars used by members of the Politburo of the Central Committee of the CPSU, mobile phones were installed. They were installed in police cars and radio taxis. In order for mobile communication to become mass, it took new idea her organization.
Each cell must be served by a base radio transmitter with a limited range and a fixed frequency. This makes it possible to reuse the same frequency in other cells. During a conversation, the cellular radiotelephone is connected to the base station by a radio channel, through which the telephone conversation is transmitted. Cell dimensions are determined by the maximum communication range of the radiotelephone with the base station. This maximum range is the cell radius.
The idea of mobile cellular communications is that, without leaving the coverage area of one base station, the mobile phone falls into the coverage area of any neighboring one up to the outer border of the entire network area.
For this, systems of antenna-repeaters have been created that cover their "cell" - the area of the Earth's surface. For communication to be reliable, the distance between two adjacent antennas must be less than their radius of action. In cities, it is about 500 m, and in rural areas - 2-3 km. A mobile phone can receive signals from several repeater antennas at once, but it always tunes in to the strongest signal.
The idea of mobile cellular communication was also to use computer control over the telephone signal from the subscriber when he moves from one cell to another. It was computer control that made it possible to switch a mobile phone from one intermediate transmitter to another within just a thousandth of a second. Everything happens so fast that the subscriber simply does not notice it.
Computers are the central part of the mobile communication system. They look for a subscriber located in any of the cells and connect him to the telephone network. When the subscriber moves from one cell to another, they transfer the subscriber from one base station to another, and also connect the subscriber from the "foreign" cellular network to "their own" when he is in its coverage area - they perform roaming (which in English means "wandering" or "wandering").
The operation of the first cellular communication system in Europe of the NMT-450 (Nordic Mobile Telephone) standard, designed to operate in the 450 MHz band, began in 1981 in Sweden, Iceland, Denmark, Norway, Finland and Saudi Arabia. Then the operation of communication systems of the same type began in the countries of Europe and Southeast Asia. In 1985, on the basis of this standard, the NMT-900 standard of the 900 MHz band was developed, which made it possible to increase the subscriber capacity of the communication system. Similar standards have been introduced in the US, France and the UK.
However, all these standards are analog and belong to the first generation of cellular communication systems. They use an analog method of transmitting information using frequency (FM) or phase (FM) modulation, as in conventional radio stations. This method has a number of significant disadvantages, the main of which are the possibility of listening to conversations by other subscribers and the impossibility of dealing with signal fading when the subscriber moves and under the influence of the landscape and buildings. The congestion of the frequency ranges caused interference during conversations.
Therefore, by the end of the 1980s. the creation of the second generation of cellular communication systems based on digital signal processing methods began. In 1990, the GSM-900 standard was developed for the 900 MHz band, which stands for Global System for Mobile Communications. And in 1991 on GSM-based a standard was developed for the 1800 MHz band. Similar standards have been adopted in the US and Japan.
In Russia analog systems cellular communications based on the NMT-450 standard appeared 10 years late, but digital systems based on the GSM standard appeared only three years late. The NMT and GSM standards are approved in our country as federal ones. In Moscow, cellular networks based on the digital GSM standard are most actively developing, and in the regions - analog networks. GSM systems in Russia are most actively promoted on the market by three operators - MTS, Beeline and MegaFon. Today, more than 70% of all cell phones in the world are based on this standard. Russia benefited from the delay in the introduction of cellular communications. We immediately adopted the digital GSM standard. Many modern cell phones are equipped with the possibility of high-speed Internet access using the GPRS (General Packet Radio Service) standard.
Personal cellular mobile communication is becoming increasingly popular, especially among young people. Total number its users in the world exceeds 600 million subscribers.
An important advantage mobile cellular communication is the ability to use it outside the common area of your operator - roaming. For this various operators agree among themselves on the mutual possibility of using their zones for users. The subscriber, leaving the common area of his operator, automatically switches to the zones of other operators even when moving from one country to another, for example, from Russia to Germany or France. Or, while in Russia, the user can make cellular calls to any country. Thus, cellular communication provides the user with the ability to communicate by phone with any country, wherever he is.
6.3.1. Organization of a cellular network
Cell phones have ceased to be a luxury and a business necessity. They are included in our everyday life, actively changing both the style and the content of our everyday life. The basic idea of organizing a cellular telephone network is extremely simple. The entire service area is divided into pieces, honeycombs, in which there are base stations that connect mobile phones to each other and to the outside world. On the map, such a mobile communication network resembles a honeycomb, hence the name of this type of telecommunications. Phones in neighboring cells do not interfere with each other, because they operate at different frequencies, but those that are more than a cell apart simply do not hear each other due to the fact that the earth is round, and radio waves decay as they propagate.
The base station with antennas and the handset in the hands of the subscriber are always close to each other and operate at minimum power, so the phone becomes truly mobile, compact and lightweight. Between themselves, the base stations are connected by a high-speed communication line, through which our conversations come to the cellular operator. Having gathered at the head cellular station, all calls are charged and switched with recipients. Naturally, cellular operators have access to the public telephone network, and the call, if it passes outside this network, begins its journey through earthly communication lines.
Thanks to unified management, when moving from cell to cell, the phone is automatically transferred to the service of a new base station. The handover process is accompanied by a change operating frequency and takes some time, almost imperceptible during the conversation.
A mobile phone does not have a permanent residence permit, and it has to periodically register on the network, respectively, the cellular operator, even when roaming (i.e. when its subscriber travels across foreign territory), knows exactly where the device is communicating, and upon request confirms solvency phone owner.
6.3.2. Cellular analog standards
Having much in common, cellular communication systems differ significantly from each other and, first of all, they use an analog or digital form of information transmission. At first, all systems were analog, and the devices were very similar to conventional walkie-talkies. Two such systems have spread most widely around the world: the American AMPS (Advanced Mobile Phone Service) and the European NMT (Nordic Mobile Telephone). Today they still work successfully in vast areas of sparsely populated areas of large countries, when the caller density is low. These standards have a limited capacity and do not allow more than fifty people to communicate simultaneously within one cell.
AMPS operates in the 800 MHz band, NMT-450, respectively, near 450 MHz, and the NMT-900, which is actively used today in the Scandinavian countries, is about 900 MHz. In NMT, the maximum cell radius can be 40 km, in AMPS it is no more than 20 km. output power mobile handsets in the NMT-450 it reaches 2-3 W, in AMPS it does not exceed 0.6 W, for stationary and automotive versions in the NMT-450 it can reach up to 15 W, and for the base station - 50-100 W.
Sound signal in analog networks, it is not subjected to significant processing, and the communication delay is only a few tens of milliseconds for local calls. Accordingly, the sound of a human voice in such phones looks the most natural and familiar. The noise and interference characteristic of analog networks are in many ways similar to those typical for wired telephones rustles and crackles.
In analog cellular systems, the issue of privacy telephone conversations is completely open, and curious competitors can freely listen to the conversations they are interested in, not only sitting in a car under the office windows, but also being a couple of blocks from the object of observation. Moreover, “improved” models appeared almost immediately. analog phones, capable of intercepting the identification numbers of legitimate users of cellular networks. Moreover, illegal devices calling at someone else's expense were quite intelligent, and before going on the air, they checked whether the one who pays for them was in touch.
Theft has become so widespread in the world of analog cellular communications that equipment manufacturers have had to urgently complicate the procedure for identifying their subscribers. And today the problem of twins, by at least in NMTi, resolved. However, the possibility of listening even with the inclusion of "encryption" remained.
Roaming in cellular networks is possible only within the standard of your choice, since phones operating in different standards are fundamentally incompatible. Where there is desired network, so-called semi-automatic roaming takes place, requiring the participation of the owner to select desired code countries.
Until recently, NMT phones were significantly larger than their cellular counterparts, but today, thanks to the advances in electronics, only a retractable antenna sometimes betrays the fact that this is an analog standard device.
In the USA, they quickly faced the fact that the analog standard could not provide communication for everyone. And the new almost completely digital standard D-AMPS (Digital Advanced Mobile Phone Service), which replaced AMPS, with the same maximum cell radius of 20 km, increased the number of simultaneous conversations in the cell to three hundred. This was a step that significantly improved the privacy of telephone conversations and removed the problem of doubles. The transition to digital, of course, had little effect on the quality of speech. This standard allows you to quite calmly provide stable mobile communications to not too densely spaced subscribers. He did not international standard, therefore, when traveling with such a phone around the world, it is far from possible to get in touch everywhere.
The world has developed and implemented 9 analog standards operating at different frequencies and not compatible with each other. Now two of them are successfully operating: the Scandinavian NMT and the American AMPS, both of which are used in our country.
6.3.3. Evolution towards digital standards
Today there are 4 digital standards with the possibility of organizing cells with a radius of 0.5 to 20-30 km: American D-AMPS and CDMA, global pan-European GSM and purely Japanese JDC (Japan Digital Cell).
It is always more difficult for pioneers, and today, in order to stay afloat, cellular operators operating in NMT and D-AMPS have to not only reduce prices, but also offer services that these standards did not originally envisage. Autodial, caller ID, voicemail, conference calls, data transfer and even work on the Internet today have become available not only to modern digital standards.
The widespread popularity of cellular networks has forced developers to seriously think about increasing their capacity and standardization throughout the planet. Since only with the unification of phones can you safely travel around the world, staying connected thanks to automatic roaming services. By this time, the beginning of the 1990s, it was already clear that the solution of these two problems was possible only by passing to digital ways voice transmission and communication control.
The development of a global standard was taken up both in Europe and in America. The Old World and the New World went slightly different ways, and as a result, there are two standards that work not only at different frequencies, but also use fundamentally different ways separation of concurrent callers. Americans in the same frequency band where they used to work AMPS and D-AMPS, since 1995, began the introduction of CDMA (Code Division Multiple Access). With the same size of cells and the same basic infrastructure, the transition to the new standard increased the number of simultaneous calls in the cell to a thousand, increased the efficiency of the devices, significantly improved the confidentiality of negotiations and eliminated the problem of twins.
Each CDMA phone has its own individual an identification number, and it is simply impossible to change the device without the participation of a mobile operator. Apparently, this is one of the reasons why so far there have been no reports of cloning (ie duplication) of this type of phones. Notebook with numbers and your personal organizer are in the phone's integral memory, and when you change your phone, you will have to overwrite all useful information.
Digital systems pay a lot of attention to speech coding, because without data compression, digital systems will not receive an advantage in terms of the number of subscribers served. The computing capabilities of a telephone microcomputer responsible for encoding and decoding speech are far from any Pentium, and therefore it is time not to complain about the quality of speech transmission in digital mobile communication systems, but to admire the fact that the voices of various peoples of the world are transmitted in such a recognizable way.
6.3.4. CDMA and GSM
CDMA has for today top speed data transfer (14.4 kbps) and fairly good sound quality. Devices operating in this standard are quite miniature and keep in touch for a long time. This standard is now widely used in North America and South Korea. There are also operators in our country who have chosen this standard, however, the prevalence of such networks is still small, and potential roaming is very limited (and in a situation where this connection licensed as wireless only, and not legally allowed).
Most popular type The cellular communication of today is definitely GSM (Global System for Mobile Communications). This European digital standard for global mobile communications, launched in 1991 in Europe, today has de facto become the most popular standard in the world. It is spreading very quickly across our planet, and today in almost all countries, having a GSM phone in hand, you can easily make and answer calls as if you were at home. GSM was developed taking into account many years of experience in the operation of cellular networks, is focused on universal use and allows for significant modification without changing the main functions.
In GSM, the cell radius can be up to 35 km, and up to a thousand simultaneous calls are possible. The maximum pulse power of mobile handsets does not exceed 1 W, although for stationary and car versions of phones it can reach up to 20 W. Devices of this standard are by far the smallest and the longest kept in touch and waiting for a call.
Digital communication systems provide a clear and noise-free sound, only slightly distorting the timbre and intonation coloring of speech. Only with weak signal levels and unstable communication is it possible that the phone seems to be swallowing pieces of words. The gain in output power and bandwidth in the transition to digital is so significant, and speech intelligibility suffers so little that it is definitely possible to forgive telephones for digital processing of the human voice.
During a conversation, we are silent for about half the time, listening to the interlocutor. Digital systems actively use this circumstance, almost completely turning off the transmitter during speech pauses, trying not to clog the air unnecessarily and saving the battery. And so that there is no ringing silence in the ears of the speaker, the phone at this time sends a “comfortable noise” to the speaker, reminiscent of typical sounds at the other end of the wire.
On-air eavesdropping of GSM-talks is difficult, here the developers have tried their best. And the point is not only in the complex form of the signals used and the closeness of the encryption algorithms, but also in the fact that the coding procedure changes all the time, and each new call has its own key.
An interesting step in the fight for caller density was the introduction of GSM 1800, which significantly increased throughput by moving to smaller cells and expanding the frequency range. Judging by the experience of operating such networks in the largest metropolitan areas, this step completely eliminates the problem of network congestion even with the total “mobilization” of the population.
Globally, GSM operates on 900 and 1800 MHz, but not in America. The Federal Radio Commission considered free and sold to operators only a small section of the spectrum in the region of 1900 MHz, and immediately the American GSM 1900 arose. Moreover, both GSM and CDMA and even D-AMPS-cellular operators can work in this range. Today, not only "worldwide" phones are produced, operating at 1800 and 1900 MHz, but also truly omnivorous "three-band" phones that can communicate in all three GSM bands.
Cellular networks and the Internet are in many ways similar to each other, and it is no coincidence that almost all GSM phones have WAP browsers and projects for a new worldwide cellular communication standard are being actively discussed, which will have a significantly higher data transfer rate and provide quite comfortable work during world wide web thanks to a wider operating band and an increased rate of voice, image and data transmission compared to GSM and CDMA. Today, such an add-on over GSM in the form of GPRS technology has already been mastered by both Moscow operators and a speed of 40.2 kbit / s has been achieved for reception.
GSM phones use a replaceable module responsible for subscriber identification, the so-called SIM card (Subscribe Identity Module). This little chip is not only responsible for ensuring that no one calls for your money, but also contains an extensive memory that can store up to 255 numbers and names of your acquaintances. Accordingly, by moving the SIM card from one GSM phone to another, you transfer not only your address book, but also your phone number, to which another phone will actually respond.
The personalization of communications is proceeding at a rapid pace, and today it is already possible to safely move from the concept of a “work” and “home” phone to the concept of a “personal individual telephone number” that is always with you. The most logical solution to this problem is the use of SIM-cards. The versatility of this small chip allows it to be used in all new, ready-to-run and developed both cellular and satellite systems connections.
The range of services provided today by GSM operators is the most extensive, and it is constantly updated. Short text messages SMS ( short message Servic) and the ability to work on the Internet directly from the telephone keypad using a WAP browser, data and fax transmission (speed 9.6 kbps), conference calls and call forwarding, information services (prices, weather, addresses, telephones) and formation various groups users - this is not a complete list of the opportunities that the owner of a GSM phone receives.
The section on cellular standards has already been completed, and almost all operators have chosen one type of connection. In our country today there are several dozens of mobile operators serving almost two million users. The Moscow operator Bee Line, having deployed its D-AMPS network, did not begin to introduce CDMA in the same band, but took up the European GSM 1800. Another metropolitan operator, MTS, started working in GSM 900, and now they both rely on dual-band GSM 900/1800. The oldest Russian cellular network MCC, together with SOTEL, continues to cover the vast expanses of our Motherland with the NMT-450i standard, thinking about digitalization. Regional operators are successfully mastering all cellular communication standards, including CDMA. The Moscow SONET network has chosen CDMA for the time being in a stationary form, but in the future, of course, in a mobile form.
And if operators provide services in different standards, then manufacturers are trying to maximize the capabilities of cell phones, making them more functional and multi-standard. The unification of satellite, cellular and office radiotelephones in one case is in full swing today, and in the 21st century. it will be quite realistic to call in the desert via a satellite channel, in the city - via a cell phone, and in the office - via a local radio-PBX, and all this will happen over one device and a single personal number of the owner of the phone.
Leading cell phone manufacturers are guided by a single European standard - GSM. That is why their equipment is technically perfect, but relatively inexpensive. After all, they can afford to produce huge batches of phones that find sales.
A convenient addition to the cell phone was the system of short messages SMS (Short Message Service). It is used to send short messages directly to the telephone of a modern digital GSM system without the use of additional equipment, only with the help numeric keypad and cell phone screen. SMS-messages are also received on a digital display, which is equipped with any cell phone. SMS can be used in cases where a regular telephone conversation is not the most comfortable view communications (for example, in a noisy crowded train). You can send your phone number to a friend via SMS. Due to the low cost, SMS is an alternative telephone conversation. The maximum size of an SMS message is 160 characters. You can send it in several ways: by calling a special service, as well as using your GSM phone with the sending function, using the Internet. The SMS system can provide additional services: send exchange rates, weather forecasts, etc. to your GSM phone. Essentially, a GSM phone with an SMS system is an alternative to a pager.
But the SMS system is not the last word in cellular communications. In the most modern cell phones (for example, by Nokia), the Chat function appeared (in the Russian version - “dialogue”). With its help, you can communicate in real time with other cell phone owners, as is done on the Internet. Essentially, this is a new kind of SMS messaging. To do this, you compose a message to your interlocutor and send it. The text of your message appears on the displays of both cell phones - yours and your interlocutor. Then he answers you and his message is displayed on the displays. Thus, you conduct an electronic dialogue. But if your interlocutor's cell phone does not support this function, then he will receive regular SMS messages.
Cellular phones have also appeared that support high-speed Internet access via GPRS (General Packet Radio Service) - a standard for packet data transmission over radio channels, in which the phone does not need to "dial": the device constantly maintains a connection, sends and receives data packets. Cellular telephones with built-in digital cameras are also produced.
According to the research company Informa Telecoms & Media (ITM), the number of mobile users in the world in 2007 is 3.3 billion people.
Finally, the most complex and expensive devices are smartphones and communicators that combine the capabilities of a cell phone and a pocket computer.
6.3.5. Transmission technologies short messages Message Service (SMS)
Short Message Service (SMS) is by far the most common and used method of sending and receiving short messages via GSM mobile communications. SMS has proven itself as a means of communication in the direction of person - person and when sending messages, which are mainly informational in nature, from the server to the subscriber and between servers.
SMS is powered by an SMS Center (Short Message Service Center or SMSC), which acts as a databank where messages are stored and a vehicle that forwards them. Short messages are sent over the same cellular network channel as phone calls. And in the case of a network that provides packet data, messages can even be sent directly during a telephone conversation.
In the specifications for the standard short messages stated that it cannot exceed 160 characters. Theoretically, the message could be 255 times larger, but, unfortunately, none of the existing telephones can store this amount of information. On average, their memory is designed for only four complete messages.
6.3.6. Multimedia Message Service (MMS)
MMS belongs to a new generation of solutions for mobile messaging. Still not completely standardized, this service promises to add many features to phones that EMS cannot provide.
The MMS standard is intended for GPRS networks, which, unlike the simpler GSM, have a permanent connection to the network, higher bandwidth and packet data capability, which, together with more powerful devices and provides a transition to multimedia messages.
MMS operation is based on SMS and e-mail standards. It incorporates the best of both systems, resulting in a "hybrid" standard optimized for use with mobile devices. This makes it easier to integrate with existing systems, applications and, most importantly, users. One of the advantages of the new standard is that both phone numbers and e-mail addresses can be used when sending a message.
The Multimedia Message Service standard allows you to include text, pictures in JPEG format, audio files compressed with an AMR encoder, an SMS message hidden inside an MMS.
In the future, MMS plans to add support for video formats and add-ons such as the Synchronized Multimedia Integration Language (SMIL), which will allow media to be presented in a structured form.
Just as SMS requires a service center to store and send messages, MMS requires a service center to manage the flow of multimedia messages.
The MMS Center (called MMS Relay/Server in the documentation) is responsible for the following set of tasks:
Receiving and sending media messages from and to mobile devices;
Converting media formats depending on the capabilities of the telephone to which the message is sent;
Generation of account information;
Receiving and delivering messages from and to foreign MMS centers;
Receiving and delivering messages from and to external systems, such as email;
Receiving and delivering messages to external providers providing additional services.
