Mobile cellular communication. The principle of operation of cellular communications What about cellular networks

cellular

cellular, mobile network- one of the types of mobile radio communications, which is based on cellular network. Key Feature lies in the fact 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 made up of them looks like a honeycomb with hexagonal cells (honeycombs).

The network consists of spatially dispersed transceivers operating in the same frequency range, and switching equipment that makes it possible to determine the current location of mobile subscribers and ensure continuity of communication when a subscriber moves from the coverage area of ​​one transceiver to the coverage area of ​​another.

Story

The first use of mobile telephone radio in the United States dates back to 1921: Detroit police used one-way dispatch communications in the 2 MHz band to transmit information from a central transmitter to vehicle-mounted receivers. In 1933, the NYPD began using a two-way mobile telephone radio system, also in the 2 MHz band. In 1934, the US Federal Communications Commission allocated 4 channels for telephone radio communications in the range of 30-40 MHz, and in 1940 about 10 thousand police vehicles were already using telephone radio communications. All of these systems used amplitude modulation. Frequency modulation began to be used in 1940 and by 1946 it had completely replaced amplitude modulation. The first public mobile radiotelephone appeared in 1946 (St. Louis, USA; Bell Telephone Laboratories), it used the 150 MHz band. In 1955, an 11-channel system began operating in the 150 MHz band, and in 1956, a 12-channel system in the 450 MHz band began operating. Both of these systems were simplex and used manual switching. Automatic duplex systems began operating in 1964 (150 MHz) and 1969 (450 MHz), respectively.

In the USSR in 1957, Moscow engineer L.I. Kupriyanovich created a prototype of a portable automatic duplex mobile radiotelephone LK-1 and a base station for it. The mobile radiotelephone weighed about three kilograms and had a range of 20-30 km. In 1958, Kupriyanovich created improved models of the device, weighing 0.5 kg and the size of a cigarette box. In the 1960s Hristo Bochvarov in Bulgaria demonstrates his prototype of a pocket mobile radiotelephone. At the Interorgtekhnika-66 exhibition, Bulgaria presents a kit for organizing local mobile communications from pocket mobile phones RAT-0.5 and ATRT-0.5 and base station RATC-10, providing connection for 10 subscribers.

At the end of the 50s in the USSR, the development of the Altai car radiotelephone system began, which was put into trial operation in 1963. The Altai system initially operated at a frequency of 150 MHz. In 1970, the Altai system operated in 30 cities of the USSR and the 330 MHz range was allocated for it.

In a similar way, with natural differences and on a smaller scale, the situation developed in other countries. Thus, in Norway, public telephone radio has been used for maritime mobile communications since 1931; in 1955 there were 27 coast radio stations in the country. Land mobile communications began to develop after the Second World War in the form of private, manually switched networks. Thus, by 1970, mobile telephone radio communications, on the one hand, had already become quite widespread, but on the other, it clearly could not keep up with the rapidly growing needs, with a limited number of channels in strictly defined frequency bands. A solution was found in the form of a cellular communication system, which made it possible to dramatically increase capacity by reusing frequencies in a system with a cellular structure.

Cellular systems

Certain elements of the cellular communication system existed before. In particular, some semblance of a cellular system was used in 1949 in Detroit (USA) by a taxi dispatch service - with the reuse of frequencies in different cells when users manually switched channels at predetermined locations. However, the architecture of what is now known as the cellular communications system was not outlined until the Bell System technical report submitted to the FCC in December 1971. From this time on, the development of cellular communications itself began.

In 1974, the US Federal Communications Commission decided to allocate a frequency band of 40 MHz in the 800 MHz band for cellular communications; in 1986 another 10 MHz was added in the same range. In 1978, tests of the first experimental cellular communication system for 2 thousand subscribers began in Chicago. Therefore, 1978 can be considered the year of the beginning of the practical use of cellular communications. The first automated commercial cellular telephone system was introduced in Chicago in October 1983 by American Telephone and Telegraph (AT&T). In Canada cellular used since 1978, in Japan - since 1979, in northern European countries (Denmark, Norway, Sweden, Finland) - since 1981, in Spain and England - since 1982. As of July 1997, cellular communications operated in more than 140 countries on all continents, serving more than 150 million subscribers.

The first commercially successful cellular network was the Finnish Autoradiopuhelin (ARP) network. This name is translated into Russian as “Car radiotelephone”. Launched in 1971, it reached 100% coverage in Finland in 1978, and in 1986 it had more than 30 thousand subscribers. The network operated at a frequency of 150 MHz, the cell size was about 30 km.

Operating principle of cellular communication

The main components of a cellular network are cell phones and base stations, which are usually located on the roofs of buildings and towers. When turned on, the cell phone listens to the airwaves, finding a signal from the base station. The phone then sends its unique identification code to the station. The telephone and the station maintain constant radio contact, periodically exchanging packets. Communication between the phone and the station can be via an analog protocol (AMPS, NAMPS, NMT-450) or digital (DAMPS, CDMA, GSM, UMTS). If the phone leaves the range of the base station (or the quality of the radio signal from the service cell deteriorates), it establishes communication with another one. handover).

Cellular networks can consist of base stations of different standards, which allows optimizing network operation and improving its coverage.

Cellular networks different operators connected to each other, as well as to the landline telephone network. This allows subscribers of one operator to make calls to subscribers of another operator, from mobile phones to landlines and from landlines to mobiles.

Operators can enter into roaming agreements among themselves. Thanks to such agreements, a subscriber, being outside the coverage area of ​​his network, can make and receive calls through the network of another operator. As a rule, this is carried out at increased rates. The possibility of roaming appeared only in 2G standards and is one of the main differences from 1G networks.

The head of the Regional Journalism Club, Irina Yasina, recalls:

By July 1997, the total number of subscribers in Russia was about 300 thousand. As of 2007, the main cellular communication protocols used in Russia are GSM-900 and GSM-1800. In addition, CDMA networks also operate in the CDMA-2000 standard, also known as IMT-MC-450. GSM operators are also making a smooth transition to the UMTS standard. In particular, the first fragment of a network of this standard in Russia was put into operation on October 2, 2007 in St. Petersburg by MegaFon.

The IDC company, based on a study of the Russian cellular communications market, concluded that in 2005 the total duration of calls on a cell phone by residents of the Russian Federation reached 155 billion minutes, and 15 billion text messages were sent.

According to data from the British research company Informa Telecoms & Media for 2006, the average cost of a minute of cellular communication for a consumer in Russia was $0.05 - this is the lowest among the G8 countries.

In December 2007, the number of cellular users in Russia increased to 172.87 million subscribers, in Moscow - to 29.9, in St. Petersburg - to 9.7 million. Penetration level in Russia - up to 119.1%, Moscow - 176%, St. Petersburg - 153%. In December 2011, the penetration level in Russia was up to 156%, Moscow - 212.1%, St. Petersburg - 215.6%. The market share of the largest cellular operators as of December 2007 was: MTS 30.9%, VimpelCom 29.2%, MegaFon 19.9%, other operators 20%.

According to a study by J"son & Partners, the number of SIM cards registered in Russia as of the end of November 2008 reached 183.8 million. This figure is due to the lack subscription fee on popular tariff plans at Russian operators cellular communications and low cost of network connection. In some cases, subscribers have SIM cards from different operators, but may not use them for a long time, or use one SIM card in a business mobile phone and the other for personal conversations.

In Russia in December 2008, there were 187.8 million cellular users (based on the number of SIM cards sold). The penetration rate of cellular communications (the number of SIM cards per 100 inhabitants) on this date was thus 129.4%. In the regions, excluding Moscow, the penetration level exceeded 119.7%.

The penetration level at the end of 2009 reached 162.4%.

As of April 2010, market share in Russia by subscribers: MTS - 32.9%, MegaFon - 24.6%, VimpelCom - 24.0%, Tele2 - 7.5%, other operators - 11.0%

Cellular services

Mobile operators provide the following services:

• Voice call;
• Caller ID (Automatic Caller ID) and Anti-Caller ID;
• Reception and transmission of multimedia messages - images, melodies, videos (MMS service);
• Access to the Internet ;
• Video call and video conference

see also

Notes

Links

• The basis of a cellular network - how base stations are built - review article on the website 3Dnews.ru (Russian)
• Cellular Communications Control Center - a view from the inside - review article on the website 3Dnews.ru (Russian)
• MAIN INDICATORS OF THE DEVELOPMENT OF PUBLIC TELEPHONE COMMUNICATIONS AND MOBILE COMMUNICATIONS (at the end of 2009)

cellular in Russia
Operators
...virtual
Sales networks
Standards

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See what “Cellular communications” is in other dictionaries:

- (English cellular phone, mobile radio relay communication), a type of radiotelephone communication in which the end devices, mobile phones (see MOBILE PHONE) are connected to each other using a cellular network of a set of special transceivers... ... encyclopedic Dictionary

One of the types of mobile radio communications, 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). Honeycombs partially... ... Dictionary of business terms

Third generation cellular communications- Third generation cellular networks (3rd Generation, or 3G) operate at frequencies in the range of about 2 gigahertz and provide data transmission at speeds of up to 2 megabits per second. Such characteristics allow you to use a mobile phone in... ... Encyclopedia of Newsmakers

LLC "Ekaterinburg 2000" Type Cellular operator Location... Wikipedia

The article contains errors and/or typos. It is necessary to check the content of the article for compliance with the grammatical norms of the Russian language... Wikipedia

It is difficult to imagine a person today who can live without cellular communications. Every day people call each other, send millions of messages, go online using mobile phones. Mobile 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. In Russia there are more than a hundred operating mobile operators. Some regional providers are subsidiaries of large Russian mobile operators.

According to statistics, the leaders among companies providing mobile communication services include 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.

1. MTS. The only “cell phone” that is among the 20 world leaders. At the end 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 stores in the country (more than 5,700 points).
2. Megaphone. There are more than 76 million subscribers in Russia, and there is great demand for Megafon SIM cards in Abkhazia, Tajikistan, and South Ossetia. The company positions itself as the operator with the fastest mobile Internet.
3. Beeline. The Vimpelcom OJSC brand is among the top hundred recognizable brands in the world. The number of subscribers in Russia reaches 59 million people, but Beeline leads in 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 “big three”, but in terms of popularity they constitute significant competition. The rating of cellular operators includes smaller companies, new ones, and regional ones. The very concept of the “Big Three” is becoming obsolete, because Other providers are also conquering the market:

• Tinkoff Mobile is one of the newcomers to the communications market, which offers its users many pleasant bonuses: selection of an individual tariff without unnecessary services And pitfalls, beautiful rooms, available roaming. Also, importantly, the operator provides high-quality communication. And when you replenish your account for the first time, you will receive.
• Tele2. At the end of 2017, this is the only company that increased the number of subscribers. It has been operating as a federal Russian operator since 2014 after receiving a license for communications in 3G format. The operator's audience is at least 40 million people in 65 regions of the country. The most active subscribers are in Moscow and the Moscow region, in St. Petersburg, Chelyabinsk and Nizhny Novgorod regions. It ranks 3rd in Russia in terms of the number of base stations, and is distinguished by fast mobile Internet due to low network load, as well as affordable package tariffs with the Internet.
• Yota is a virtual cellular operator. The brand has existed since 2008. Powered by Megafon technical infrastructure. The subscriber base is about 1.5 million people. Until January 2017, the only operator with unlimited access to the mobile Internet, today the tariff line includes only products with a limited amount of traffic for smartphones, and for tablets and computers there are offers with unlimited internet, the price of which depends on the speed.
• Rostelecom is an Internet provider and company providing home wireline and cable television services. The company offers its subscribers cellular communications in GSM 900/1800 format and mobile Internet.
• "Motiv" serves only 4 regions in the Ural Federal District. This trademark exists since 2002. The company provides communications in GPRS / EDGE, IVR, MMS, SMS, USSD formats, but is not represented in Moscow.
• "SMARTS" is a Samara company. Communications in Russia are provided to subscribers from the Volga region and central regions of the country. The list of services includes GPRS, CSD data transmission, communication in GSM-900, GSM-1800 standards, SMS, MMS transmission.

Before choosing a cellular operator, each client must outline his own range of preferences and outline the requirements for mobile communications. Each provider is good in its own way; the best cellular operator can have regional status if the package of services it provides meets the client’s needs.

A list of communications within Russia, a telephone code and a comparison of operators will help you choose a suitable provider.

Map of mobile operators

Communications companies are sensitive to increasing customer demands. Now it is no longer only major players in the telecommunications market that offer high-quality communication coverage. The emergence of new towers makes it possible to provide communications to even the most remote settlements; you can now use a mobile phone in the subway and in high-rise buildings. 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 fighting to retain existing subscribers and expand its consumer base, so 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 has a database of 11-digit numbers, which can be used to determine the operator and regions of connection of the number. Not all subscribers took advantage of the opportunity to switch from one operator to another, which appeared after the abolition of “mobile slavery,” so the table of codes helps 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 connection to the region, like other large operators. The company has separate codes only for the Far East and Primorsky Territory. But Yota’s numbers are not tied to the region; they all start with the code 999.

In the North-West region and St. Petersburg

Southern Federal District, including the North Caucasus

The tables indicate both codes designed for all regions, and those that apply only to the specified city or region. But large operators have codes for certain areas, i.e. cellular services will be cheaper only when used in your home region.

The place of registration of numbers with codes 950, 951, 952 with Tele2 can be the Irkutsk region, Khanty-Mansiysk region, Lipetsk region, Kursk region, Perm region, 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 telephone number of any Russian operator begins with 8, to dial in international format you need to dial +7. However, inside Russia, the call will be equally successful when dialing from both eight and +7.

The international code is followed by prefix numbers - this is the DEF code used in mobile networks. The prefixes of Russian operators begin with 9, i.e. the general form of the code is always this: 9хх. For companies providing mobile communication services, one or more such codes are allocated. This makes it possible to determine the operator and region of the caller: 926, 916, 977 are Moscow numbers, and 911, 921 or 981 are St. Petersburg numbers.

For the “mobile three” there are a series of codes in which the second digits also match. For example, 91x or 98x are MTS numbers, and 92x or 93x are Megafon numbers.

The next 7 digits are the subscriber number, by which it is impossible to determine belonging to the region of residence or provider. The range of Beeline numbers can indicate region membership 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 number help determine the operator. For example, DEF code 958 is used by more than 20 operators, including small companies (covering 1 region and a capacity of 10,000 numbers) and large ones (several dozen regions and hundreds of thousands of numbers).

As an example: the prefix of the TransTelecom company numbers is 7958, but since the company serves 30 regions of the country, you need to know the initial digits of the subscriber number in order to determine the origin of the outgoing call (-00х-хх-хх - Bashkiria, and -03х-хх-хх - Kaliningrad region, etc.).

The same prefix is ​​used by Gazprom Telecom, Business Network Irkutsk, State Unitary Enterprise Avtomaticheskaya telephone exchange Smolny", "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 used only by Megafon 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 different calibers in terms of capacity and regional coverage - Antares, Arkhangelsk Mobile Networks", "Ekaterinburg-2000", "Kemerovo Mobile Communications", "Sky-1800", etc.

"Tele2" is the largest of the companies that use the prefix 900: "T2 Mobile" - these are 17 regions and 3,140,000 numbers (the region is determined by the digits of the subscriber number), "Tele2-Omsk" - 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

Ratings of companies providing cellular communication services are compiled not only taking into account the number of subscribers and the scope of the coverage area, but also the list of services provided by the company and the tariffs established for each item or the entire package.

Advertising campaigns of the four leading providers (MTS, Megafon, Tele2, Beeline) are aimed at attracting subscribers, therefore TV commercials vying with each other to prove that the tariffs of one or another company are the most favorable. Telecom operators' tariffs dynamically reflect company strategy, consumer preferences and industry trends. At the same time, archived tariffs are also valid until the subscriber switches to a new price offer.

Budget rates

	MTS, Smart	Megaphone, Get involved! Choose	Beeline, First gigs	Tele 2, "My Conversation"
Cost, rub.)	400	450	405	200
Package of minutes	200	300	400	200
Internet (GB)	4	6	4	2

It’s not difficult to get lost in such variety, 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 communications, 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 determine the needs of the subscriber (mobile Internet, calls to home network, roaming, etc.).

I have been following new developments in the field for many years now. mobile technologies. Previously, this was my hobby, but now it has grown into a professional blog, where I am happy to share the information I have accumulated with you. All instructions, life hacks, selections best programs and tariff plans I checked personally on myself.

Useful services that can be connected along with the tariff or already during use

Transfer minutes, GB and SMS to the next month

The balances of the main packages of minutes, SMS and GB included in the monthly fee that are unused in the current billing period are transferred. Carry-over balances can be used during the next billing period. First of all, the transferred balances of minutes, SMS and GB are consumed, then - service packages included in the tariff plan. Transfers are only possible if the monthly fee set for your plan is paid on time.

Not available on Whole Story, Family Story, or Neverending Story plans

Exchange minutes to GB

Get more Internet by exchanging unused minutes from the package for additional gigabytes.

You can exchange minutes:

Basic package included in the tariff;

Received as part of the transfer of balances.

Exchange rate:

• 1 minute = 10.24 MB;
• 10 minutes = 102.4 MB;
• 100 minutes = 1 GB

The service is free, but is provided only if the subscription fee established for the connected tariff is charged.

The service is not provided while the “Add traffic”/ “500MB+” options are in effect

First of all, Internet traffic from the transferred package is consumed, after it is exhausted - from the main Internet traffic package.

The volume of Internet traffic received in exchange for minutes is transferred to the next billing period, but not more than twice the volume of the main package provided in accordance with the terms of the tariff plan. When changing the tariff plan, unused Internet traffic is burned.

The service can be used throughout Russia, with the exception of the Republic of Crimea and the city of Sevastopol.

Not available on tariff plans: “New story. Online”, “Whole story”, “Family story”; "SUPER SIM S", "For Unlimited" and "Endless Story", including archival ones.

Find out the number of minutes available for exchange *108# View the exchange history of minutes *108*0# Exchange minutes for GB *108*number of minutes#

Local number without extra charge

Available in Family Story, Whole Story and Neverending Story plans

mobile connection- this is radio communication between subscribers, the location of one or more of which changes. One type of mobile communication is cellular communication.

cellular- one of the types of radio communications, which is based on a cellular network. Key Feature: The total coverage area is divided into cells determined by coverage areas base stations. The cells overlap and together form a network. On an ideal surface, the coverage area of ​​one base station is a circle, so the network made up of them looks like cells with hexagonal cells.

Operating principle of cellular communication

So, first, let's look at how a call is made on a mobile phone. As soon as the user dials a number, the handset (HS - Hand Set) begins searching for the nearest base station (BS - Base Station) - the transceiver, control and communication equipment that makes up the network. It consists of a base station controller (BSC - Base Station Controller) and several repeaters (BTS - Base Transceiver Station). Base stations are controlled by a mobile switching center (MSC - Mobile Service Center). Thanks to cellular structure, repeaters cover the area with a zone of reliable reception in one or more radio channels with an additional service channel through which synchronization occurs. More precisely, the exchange protocol between the device and the base station is agreed upon by analogy with the modem synchronization procedure (handshacking), during which the devices agree on the transmission speed, channel, etc. When the mobile device finds a base station and synchronization occurs, the base station controller forms a full-duplex link to the mobile switching center through the fixed network. The center transmits information about the mobile terminal to four registers: the Visitor Layer Register (VLR), the Home Register Layer (HRL), and the Subscriber or Authentication Register (AUC). and equipment identification register (EIR - Equipment Identification Register). This information is unique and is located in the plastic subscription box. microelectronic telecard or module (SIM - Subscriber Identity Module), which is used to check the subscriber’s eligibility and tariffication. Unlike landlines, for the use of which a fee is charged depending on the load (number of busy channels) received via a fixed subscriber line, the fee for the use of mobile communications is not charged from the user telephone set, but from a SIM card that can be inserted into any device.

The card is nothing more than a regular flash chip, made using smart technology (SmartVoltage) and having the necessary external interface. It can be used in any device, and the main thing is that the operating voltage matches: early versions used a 5.5V interface, while modern cards usually have 3.3V. The information is stored in the standard of a unique international subscriber identifier (IMSI - International Mobile Subscriber Identification), which eliminates the possibility of "doubles" - even if the card code is accidentally selected, the system will automatically exclude the fake SIM, and you will not have to subsequently pay for other people's calls. When developing the cellular communication protocol standard, this point was initially taken into account, and now each subscriber has its own unique and only identification number in the world, encoded during transmission with a 64-bit key. In addition, by analogy with scramblers designed to encrypt/decrypt a conversation in analog telephony, 56bit coding is used in cellular communications.

Based on this data, the system’s idea of ​​the mobile user is formed (his location, status on the network, etc.) and the connection occurs. If during a conversation a mobile user moves from the coverage area of ​​one repeater to the coverage area of ​​another, or even between the coverage areas of different controllers, the connection is not interrupted or deteriorated, since the system automatically selects the base station with which the connection is better. Depending on the channel load, the phone selects between a 900 and 1800 MHz network, and switching is possible even during a conversation, completely unnoticed by the speaker.

Call from normal telephone network to the mobile user is carried out in the reverse order: first, the location and status of the subscriber are determined based on constantly updated data in the registers, and then the connection and maintenance of communication occur.

Mobile radio communication systems are built according to a point-multipoint scheme, since the subscriber can be located at any point in the cell controlled by the base station. In the simplest case of circular transmission, the power of a radio signal in free space theoretically decreases in inverse proportion to the square of the distance. However, in practice, the signal attenuates much faster - in the best case, proportional to the cube of the distance, since the signal energy can be absorbed or reduced by various physical obstacles, and the nature of such processes strongly depends on the transmission frequency. When the power decreases by an order of magnitude, the covered area of ​​the cell decreases by two orders of magnitude.

"PHYSIOLOGY"

The most important reasons for increased signal attenuation are shadow areas created by buildings or natural elevations in the area. Studies of the conditions for the use of mobile radio communications in cities have shown that even at very close distances, shadow zones provide attenuation of up to 20 dB. Another important reason the attenuation is the foliage of the trees. For example, at a frequency of 836 MHz in the summer, when the trees are covered with leaves, the received signal level is approximately 10 dB lower than at the same place in the winter, when there are no leaves. The fading of signals from shadow zones is sometimes called slow in terms of the conditions for their reception in motion when crossing such a zone.

An important phenomenon that has to be taken into account when creating cellular mobile radio communication systems is the reflection of radio waves, and, as a consequence, their multipath propagation. On the one hand, this phenomenon is useful, since it allows radio waves to bend around obstacles and propagate behind buildings, in underground garages and tunnels. But on the other hand, multipath propagation gives rise to such difficult problems for radio communications as extended signal delay, Rayleigh fading and worsening of the Doppler effect.

Signal delay stretching occurs due to the fact that a signal passing along several independent paths of different lengths is received several times. Therefore, a repeated pulse can go beyond the time interval allotted for it and distort the next character. Distortion caused by extended delay is called intersymbol interference. At short distances extended delay is not dangerous, but if the cell is surrounded by mountains, the delay can extend for many microseconds (sometimes 50-100 µs).

Rayleigh fading is caused by the random phases with which the reflected signals arrive. If, for example, the direct and reflected signals are received in antiphase (with a phase shift of 180°), then the total signal can be attenuated almost to zero. Rayleigh fading for of this transmitter and a given frequency are something like amplitude “dips”, having different depths and randomly distributed. In this case, with a stationary receiver, fading can be avoided simply by moving the antenna. When a vehicle is moving, thousands of such “dips” occur every second, which is why the resulting fading is called fast.

The Doppler effect manifests itself when the receiver moves relative to the transmitter and consists of a change in the frequency of the received oscillation. Just as the pitch of a moving train or car appears slightly higher to a stationary observer as the vehicle approaches and slightly lower as it moves away, the frequency of a radio transmission shifts as the transceiver moves. Moreover, with multipath signal propagation, individual rays can produce a frequency shift in one direction or another at the same time. As a result, due to the Doppler effect, random frequency modulation of the transmitted signal is obtained, just as random amplitude modulation occurs due to Rayleigh fading. Thus, in general, multipath propagation creates great difficulties in organizing cellular communications, especially for mobile subscribers, which is associated with slow and fast fading of the signal amplitude in a moving receiver. These difficulties were overcome with the help of digital technology, which made it possible to create new methods of coding, modulation and equalization of channel characteristics.

"ANATOMY"

Data transmission is carried out via radio channels. The GSM network operates in the 900 or 1800 MHz frequency bands. More specifically, for example, in the case of considering the 900 MHz band, the mobile subscriber unit transmits on one of the frequencies lying in the range 890-915 MHz, and receives on a frequency lying in the range 935-960 MHz. For other frequencies the principle is the same, only the numerical characteristics change.

By analogy with satellite channels, the direction of transmission from the subscriber device to the base station is called upward (Rise), and the direction from the base station to the subscriber device is called downward (Fall). In a duplex channel consisting of upstream and downstream transmission directions, frequencies differing by exactly 45 MHz are used for each of these directions. In each of the above frequency ranges, 124 radio channels are created (124 for receiving and 124 for transmitting data, spaced at 45 MHz) with a width of 200 kHz each. These channels are assigned numbers (N) from 0 to 123. Then the frequencies of the upstream (F R) and downstream (F F) directions of each channel can be calculated using the formulas: F R (N) = 890+0.2N (MHz), F F (N) = F R (N) + 45 (MHz).

Each base station can be provided with from one to 16 frequencies, and the number of frequencies and transmission power are determined depending on local conditions and load.

In each of the frequency channels, which is assigned a number (N) and which occupies a 200 kHz band, eight time division channels (time channels with numbers from 0 to 7), or eight channel intervals, are organized.

The frequency division system (FDMA) allows you to get 8 channels of 25 kHz, which, in turn, are divided according to the principle of the time division system (TDMA) into another 8 channels. GSM uses GMSK modulation and the carrier frequency changes 217 times per second to compensate for possible quality degradation.

When a subscriber receives a channel, he is allocated not only a frequency channel, but also one of the specific channel slots, and he must transmit in a strictly allotted time interval, without going beyond it - otherwise interference will be created in other channels. In accordance with the above, the transmitter operates in the form of individual pulses, which occur in a strictly designated channel interval: the duration of the channel interval is 577 μs, and the duration of the entire cycle is 4616 μs. Allocation to the subscriber of only one of the eight channel intervals allows the process of transmission and reception to be divided in time by shifting the channel intervals allocated to the transmitters of the mobile device and the base station. The base station (BS) always transmits three timeslots before the mobile unit (HS).

The requirements for the characteristics of a standard pulse are described in the form of a normative pattern of changes in radiation power over time. The processes of turning the pulse on and off, which are accompanied by a change in power by 70 dB, must fit into a time period of only 28 μs, and the working time during which 147 binary bits are transmitted is 542.8 μs. The transmission power values ​​​​indicated in the table earlier refer specifically to the pulse power. The average power of the transmitter turns out to be eight times less, since the transmitter does not radiate 7/8 of the time.

Let's consider the format of a normal standard pulse. It shows that not all discharges carry useful information: Here, a 26-bit training sequence is placed in the middle of the pulse to protect the signal from multipath interference. This is one of eight special, easily recognizable sequences in which the received bits are correctly positioned in time. Such a sequence is fenced with single-bit pointers (PB - Point Bit), and on both sides of this training sequence there is useful encoded information in the form of two blocks of 57 binary bits, fenced, in turn, with boundary bits (BB - Border Bit) - 3 bits each each side. Thus, a pulse carries 148 bits of data, which takes up a 546.12 µs time interval. To this time is added a period equal to 30.44 μs of protective time (ST - Shield Time), during which the transmitter is “silent”. In terms of duration, this period corresponds to the time of transmission of 8.25 bits, but no transmission occurs at this time.

The sequence of pulses forms a physical transmission channel, which is characterized by a frequency number and a time channel slot number. Based on this sequence of pulses, a whole series of logical channels are organized, which differ in their functions. In addition to channels transmitting useful information, there are also a number of channels transmitting control signals. The implementation of such channels and their operation require precise management, which is implemented by software.

Cellular communications have recently become so firmly established in our daily life that it is difficult to imagine modern society without it. Like many other great inventions, the mobile phone has greatly influenced our lives and many areas of it. It is difficult to say what the future would be like if it were not for this convenient type of communication. Probably the same as in the movie "Back to the Future 2", where there are flying cars, hoverboards, and much more, but there is no cellular communication!

But today, in a special report for, there will be a story not about the future, but about how modern cellular communications are structured and work.

In order to learn about the operation of modern cellular communications in the 3G/4G format, I invited myself to visit the new federal operator Tele2 and spent the whole day with their engineers, who explained to me all the intricacies of data transmission through our mobile phones.

But first I’ll tell you a little about the history of cellular communications.

The principles of wireless communication were tested almost 70 years ago - the first public mobile radiotelephone appeared in 1946 in St. Louis, USA. In the Soviet Union, a prototype of a mobile radiotelephone was created in 1957, then scientists in other countries created similar devices with different characteristics, and only in the 70s of the last century in America were modern principles the work of cellular communications, after which its development began.

Martin Cooper - inventor of the portable prototype cell phone Motorola DynaTAC weighs 1.15 kg and measures 22.5x12.5x3.75 cm

If in Western countries by the mid-90s of the last century, cellular communications were widespread and used by most of the population, then in Russia it just began to appear, and became available to everyone a little over 10 years ago.

Bulky, brick-shaped mobile phones that worked in the first and second generation formats have become history, giving way to smartphones with 3G and 4G, better voice communications and high Internet speeds.

Why is the connection called cellular? Because the territory in which communication is provided is divided into separate cells or cells, in the center of which base stations (BS) are located. In each “cell” the subscriber receives the same set of services within certain territorial boundaries. This means that moving from one cell to another, the subscriber does not feel territorial attachment and can freely use communication services.

It is very important that there is continuity of connection when moving. This is ensured thanks to the so-called handover, in which the connection established by the subscriber is, as it were, picked up by neighboring cells in a relay race, and the subscriber continues to talk or delve into social networks.

The entire network is divided into two subsystems: the base station subsystem and the switching subsystem. Schematically it looks like this:

In the middle of the "cell", as mentioned above, there is a base station, which usually serves three "cells". The radio signal from the base station is emitted through 3 sector antennas, each of which is aimed at its own “cell”. It happens that several antennas of one base station are directed at one “cell”. This is due to the fact that the cellular network operates in several bands (900 and 1800 MHz). In addition, a given base station may contain equipment from several generations of communications (2G and 3G).

But on Tele2 BS towers there is equipment only of the third and fourth generation- 3G/4G, since the company decided to abandon old formats in favor of new ones that help avoid interruptions voice communication and provide a more stable Internet. Regulars of social networks will support me in the fact that nowadays Internet speed is very important, 100-200 kb/s is no longer enough, as it was a couple of years ago.

The most common location for a BS is a tower or mast built specifically for it. Surely you could see red and white BS towers somewhere far from residential buildings (in a field, on a hill), or where there are no tall buildings nearby. Like this one, which is visible from my window.

However, in urban areas it is difficult to find a place to place a massive structure. Therefore, in large cities, base stations are located on buildings. Each station picks up signals from mobile phones at a distance of up to 35 km.

These are antennas, the BS equipment itself is located in the attic, or in a container on the roof, which is a pair of iron cabinets.

Some base stations are located in places you wouldn't even guess. Like, for example, on the roof of this parking lot.

The BS antenna consists of several sectors, each of which receives/sends a signal in its own direction. If the vertical antenna communicates with phones, then the round antenna connects the BS to the controller.

Depending on the characteristics, each sector can handle up to 72 calls simultaneously. A BS can consist of 6 sectors and serve up to 432 calls, but usually fewer transmitters and sectors are installed at stations. Cellular operators such as Tele2 prefer to install more BS to improve the quality of communication. As I was told, the most modern equipment is used here: Ericsson base stations, transport network - Alcatel Lucent.

From the base station subsystem, the signal is transmitted towards the switching subsystem, where a connection is established in the direction desired by the subscriber. The switching subsystem has a number of databases that store subscriber information. In addition, this subsystem is responsible for security. To put it simply, the switch is complete It has the same functions as the female operators who used to connect you with the subscriber with their hands, only now all this happens automatically.

The equipment for this base station is hidden in this iron cabinet.

In addition to conventional towers, there are also mobile versions of base stations located on trucks. They are very convenient to use during natural disasters or in crowded places (football stadiums, central squares) during holidays, concerts and various events. But, unfortunately, due to problems in legislation, they have not yet found wide application.

To ensure optimal radio signal coverage at ground level, base stations are designed in a special way, therefore, despite the range of 35 km. the signal does not extend to aircraft flight altitude. However, some airlines have already begun installing small base stations on their boards that provide cellular communications inside the aircraft. Such a BS is connected to a terrestrial cellular network using satellite channel. The system is complemented by a control panel that allows the crew to turn the system on and off, as well as certain types of services, for example, turning off the voice on night flights.

I also looked into the Tele2 office to see how specialists monitor the quality of cellular communications. If a few years ago such a room would have been hung to the ceiling with monitors showing network data (load, network failures, etc.), then over time the need for so many monitors has disappeared.

Technologies have developed greatly over time, and such a small room with several specialists is enough to monitor the work of the entire network in Moscow.

Some views from the Tele2 office.

At a meeting of company employees, plans to capture the capital are discussed) From the beginning of construction until today, Tele2 has managed to cover all of Moscow with its network, and is gradually conquering the Moscow region, launching more than 100 base stations weekly. Since I now live in the region, it is very important to me. so that this network comes to my town as quickly as possible.

The company's plans for 2016 include providing high-speed communications in the metro at all stations; at the beginning of 2016, Tele2 communications are present at 11 stations: 3G/4G communications at the Borisovo, Delovoy Tsentr, Kotelniki, and Lermontovsky Prospekt metro stations. , “Troparevo”, “Shipilovskaya”, “Zyablikovo”, 3G: “Belorusskaya” (Ring), “Spartak”, “Pyatnitskoye Shosse”, “Zhulebino”.

As I said above, Tele2 abandoned the GSM format in favor of third and fourth generation standards - 3G/4G. This allows you to install 3G/4G base stations with a higher frequency (for example, inside the Moscow Ring Road, BSs are located at a distance of about 500 meters from each other) to provide more stable communications and high speed mobile internet, which was not the case in networks of previous formats.

From the company’s office, I, in the company of engineers Nikifor and Vladimir, go to one of the points where they need to measure the communication speed. Nikifor stands in front of one of the masts on which communication equipment is installed. If you look closely, you will notice a little further to the left another such mast, with equipment from other cellular operators.

Oddly enough, cellular operators often allow their competitors to use their tower structures to place antennas (naturally on mutually beneficial terms). This is because building a tower or mast is an expensive proposition, and such an exchange can save a lot of money!

While we were measuring the communication speed, Nikifor was asked several times by passing grandmothers and uncles if he was a spy)) “Yes, we are jamming Radio Liberty!”

The equipment actually looks unusual; from its appearance one can assume anything.

The company’s specialists have a lot of work to do, considering that the company has more than 7 thousand in Moscow and the region. base stations: about 5 thousand of them. 3G and about 2 thousand. LTE base stations, and recently the number of base stations has increased by about a thousand.
In just three months, 55% of the total number of new operator base stations in the region were put on air in the Moscow region. Currently, the company provides high-quality coverage of the territory where more than 90% of the population of Moscow and the Moscow region lives.
By the way, in December, Tele2’s 3G network was recognized as the best in quality among all capital operators.

But I decided to personally check how good Tele2’s connection is, so I bought a SIM card in the nearest shopping center on Voykovskaya metro station, with the simplest tariff “Very Black” for 299 rubles (400 SMS/minutes and 4 GB). By the way, I had a similar Beeline tariff, which was 100 rubles more expensive.

I checked the speed without going far from the cash register. Reception - 6.13 Mbps, transmission - 2.57 Mbps. Considering that I am standing in the center of a shopping center, this is a good result; Tele2 communication penetrates well through the walls of a large shopping center.

At metro Tretyakovskaya. Signal reception - 5.82 Mbps, transmission - 3.22 Mbps.

And on metro station Krasnogvardeyskaya. Reception - 6.22 Mbps, transmission - 3.77 Mbps. I measured it at the exit of the subway. If you take into account that this is the outskirts of Moscow, it’s very decent. I think that the connection is quite acceptable, we can confidently say that it is stable, considering that Tele2 appeared in Moscow just a couple of months ago.

There is a stable Tele2 connection in the capital, which is good. I really hope that they will come to the region as soon as possible and I will be able to take full advantage of their connection.

Now you know how cellular communication works!

If you have a production or service that you want to tell our readers about, write to me - Aslan ( [email protected] ) and we will make the best report, which will be seen not only by readers of the community, but also by the website http://ikaketosdelano.ru

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