Types of cellular telephone communication. Cellular services

How many of us wonder what happens after we press the call button on a mobile phone? How do cellular networks work?

Probably not. Most often, we dial the federal number of the interlocutor on the machine, as a rule, on business, so what is there and how it works does not interest us at a particular point in time. But these are amazing things. How can you call a person who is in the mountains or in the middle of the ocean? Why during a conversation we can hear each other badly, or even completely interrupt. Our article will try to shed light on the principle of cellular communications.

So, most of the densely populated territory of Russia is covered by the so-called BS, which, without abbreviation, are called Base Stations. Many could turn their attention to them, traveling between cities. In an open field, Base Stations are more like towers that are red and white. But in the city, such BS are thoughtfully placed on the roofs of non-residential skyscrapers. These towers are able to pick up a signal from any cell phone located territorially within a radius of no more than 35 kilometers. "Communication" between the BS and the phone occurs through a special service or voice channel.

As soon as a person dials the number he needs on a mobile device, the device finds the Base Station closest to him, therefore, a special service channel and asks her to allocate a voice channel. The tower, after receiving a request from the device, sends a request to the so-called controller, which we will call BSC for short. This same controller redirects the request to the switch. The smart switch MSC will determine which operator the called subscriber is connected to.

If it turns out that the call is made to a phone within the same network, for example, from a Beeline subscriber to another subscriber of this operator, or within MTS, within Megafon, and so on, the switch will begin to find out the location of the called subscriber. Thanks to the Home Location Register, the switch will find where the right person is located. It can be anywhere, at home, at work, in the country or even in another country. This will not prevent the switch from transferring the call to the appropriate switch. And then the "tangle" will begin to "unwind". That is, the call from the switch - "answerer" will go to the controller - "responder", then to its Base Station and to the mobile phone, respectively.

If the switch finds out that the called subscriber belongs to another operator, it will send a request to the switch of another network.
Agree, the scheme is quite simple, but it is difficult to imagine. How the "smart" Base Station finds the phone, sends a request, and the switch itself determines the operator and the other switch. What is a base station, really? It turns out that these are several iron cabinets that are located either under the very roof of the building, in the attic or in a special container. The main condition is that the room must be perfectly air-conditioned.

It is logical that the BS has an antenna, which helps it "catch" the connection. The BS antenna consists of several parts (sectors), each of which is responsible for the territory. The part of the antenna that is located vertically is responsible for communication with mobile phones, and the round one is for communication with the controller.

One sector is able to simultaneously receive calls from seventy telephone sets. If we take into account that one BS can consist of six sectors, then at the same time it will easily serve 6 * 72 = 432 calls.

As a rule, such power of the Base Station is enough "with a head". Of course, there are situations when the entire population of our country begins to call each other at the same time. It is a New Year. Some just need to say the cherished phrase “Happy New Year!” into the phone, while others are ready to pronounce hours with an unlimited tariff from Communications Corporation, discussing guests and plans for the whole night.

However, regardless of the duration of the call, the Base Stations cannot cope, and it can be very difficult to get through to the subscriber. But on weekdays, for most of the year, BS from six sectors is quite enough, especially for optimal workload, the operator selects Stations in accordance with the population of the territory. Some operators give their preference to large BS in order to improve the quality of the communication provided.

There are three ranges in which the BS can operate and which determine the number of supported devices and the distance covered. In the 900 MHz band, the station is able to cover a large area, but in the 1800 MHz band, the distance will be significantly reduced, but the number of connected transmitters will increase. The third band at 2100 MHz already assumes a new generation connection - 3G.
It is clear that in sparsely populated areas it is more expedient to set the Base Station at 900 MHz, but in the city 1800 MHz is suitable in order to better penetrate through thick concrete walls, and these BSs will need ten times more than in the village. Note that one BS can support three bands at once.

Stations in 900 MHz mode cover an area with a radius of 35 km, but if at the moment it serves few phones, it can "break through" up to 70 km. Naturally, our mobile phones can "find" the BS even at a distance of 70 km. Base Stations are designed to cover the earth's surface as much as possible and provide a large number of people with communication on the ground, therefore, if it is possible to catch signals at a distance of at least 35 kilometers, at the same distance, but into the sky, Base Stations do not "break through".

In order to provide their passengers with cellular communications, some airlines are starting to place small base stations on board aircraft. The connection of the "heavenly" Base Station with the "terrestrial" is carried out using a satellite channel. Since the operation of mobile devices can interfere with the flight process, on-board BS can easily be turned on / off, they have several modes of operation, up to the complete shutdown of voice messaging. During the flight, the phone may accidentally be transferred to a base station with a poorer signal or no free channels. In this case, the call will be terminated. All these are the subtleties of cellular communication in the sky in motion.

In addition to aircraft, some problems arise for residents of penthouses. Even an unlimited tariff and VIP - the conditions of a mobile operator will not help in the case of different BS. A resident of an apartment on a high floor, moving from one room to another, will lose connection. This may be due to the fact that the phone in one room "sees" one BS, and in another it "discovers" another. Therefore, during a conversation, the connection is interrupted, since these BSs are at a relative distance from each other and are not even considered "neighboring" by one operator.

Telephone communication is the transmission of speech information over long distances. Telephony allows people to communicate in real time.

If at the time of the emergence of technology there was only one method of data transmission - analog, then at the moment a variety of communication systems are successfully used. Telephone, satellite and mobile communications, as well as IP-telephony provide reliable contact between subscribers, even if they are in different parts of the world. How does telephone communication work when using each method?

Good old wired (analogue) telephony

The term "telephone" communication is most often understood as analog communication, a method of data transmission that has become familiar for almost a century and a half. When using this, information is transmitted continuously, without intermediate encoding.

The connection of two subscribers is regulated by dialing, and then communication is carried out by transmitting a signal from person to person over wires in the most literal sense of the word. Subscribers are no longer connected by telephone operators, but by robots, which greatly simplified and reduced the cost of the process, but the principle of operation of analog communication networks remained the same.

Mobile (cellular) communication

Subscribers of cellular operators mistakenly believe that they "cut the wire" connecting them to telephone exchanges. In appearance, everything is so - a person can move anywhere (within the signal coverage), without interrupting the conversation and without losing contact with the interlocutor, and<подключить телефонную связь стало легче и проще.

However, if we understand how mobile communications work, we will find not so many differences from the operation of analog networks. The signal actually "hovers in the air", only from the caller's phone it gets to the transceiver, which, in turn, communicates with the similar equipment closest to the called subscriber ... via fiber optic networks.

The data radio stage covers only the signal path from the phone to the nearest base station, which is connected to other communication networks in a completely traditional way. How cellular communication works is clear. What are its pros and cons?

The technology provides greater mobility than analog data transmission, but carries all the same risks of unwanted interference and the possibility of listening to lines.

Cell signal path

Let us consider in more detail exactly how the signal reaches the called subscriber.

1. The user dials a number.
2. His phone establishes a radio link with the nearest base station. They are located on high-rise buildings, industrial buildings and towers. Each station consists of transmitting and receiving antennas (from 1 to 12) and a control unit. Base stations that serve one area are connected to the controller.
3. From the control unit of the base station, the signal is transmitted via cable to the controller, and from there, also via cable, to the switch. This device provides signal input and output to various communication lines: long-distance, urban, international, and other mobile operators. Depending on the size of the network, it may involve either one or several switches connected to each other by wires.
4. From "its" switchboard, the signal is transmitted via high-speed cables to the switchboard of another operator, and the latter easily determines which controller the subscriber to whom the call is addressed is located in the coverage area of.
5. The switch calls the desired controller, which sends a signal to the base station, which "interrogates" the mobile phone.
6. The called party receives an incoming call.

Such a multi-layer structure of the network allows you to evenly distribute the load between all its nodes. This reduces the possibility of equipment failure and ensures uninterrupted communication.

How cellular communication works is clear. What are its pros and cons? The technology provides greater mobility than analog data transmission, but carries all the same risks of unwanted interference and the possibility of listening to lines.

Satellite connection

Let's see how satellite communications, the highest level of development of radio relay communications today, work. A repeater placed in orbit is capable of covering a vast area of ​​the planet's surface alone. A network of base stations, as in the case of cellular communications, is no longer needed.

An individual subscriber gets the opportunity to travel with virtually no restrictions, staying connected even in the taiga or the jungle. A legal entity subscriber can bind an entire mini-PBX to one repeater antenna (this is the already familiar “dish”), however, one should take into account the volume of incoming and outgoing, as well as the size of the files that need to be sent.

Technology cons:

• serious weather dependence. A magnetic storm or other cataclysm can leave a subscriber without communication for a long time.
• if something physically breaks down on a satellite transponder, the period that will pass before the functionality is fully restored will stretch for a very long time.
• the cost of communication services without borders often exceeds the more usual bills. When choosing a communication method, it is important to consider how much you need such a functional connection.

Satellite communications: pros and cons

The main feature of the "satellite" is that it provides subscribers with independence from land lines. The advantages of such an approach are obvious. These include:

• equipment mobility. It can be deployed in a very short time;
• the ability to quickly create extensive networks covering large areas;
• communication with hard-to-reach and remote territories;
• redundancy of channels that can be used in the event of a breakdown of terrestrial communications;
• the flexibility of the technical characteristics of the network, allowing it to be adapted to almost any requirements.

Technology cons:

• serious weather dependence. A magnetic storm or other cataclysm can leave a subscriber without communication for a long time;
• if something is physically out of order on the satellite transponder, the period that will pass until the system functionality is fully restored will stretch for a long time;
• the cost of communication services without borders often exceeds the more usual bills.

When choosing a communication method, it is important to consider how much you need such a functional connection.

We all use mobile phones, but rarely does anyone think - how do they work? In this article, we will try to figure out how communication is actually implemented with respect to your mobile operator.

When you make a call to your interlocutor, or someone calls you, your phone is connected via radio to one of the antennas nearby base station (BS, BS, Base Station).Each cellular base station (in the common people - cell towers) includes from one to twelve transceivers antennas having directions in different directions in order to provide high-quality communication to subscribers within their range. Specialists in their jargon call such antennas "sectors", which are gray rectangular structures that you can see almost every day on the roofs of buildings or special masts.

The signal from such an antenna is sent via cable directly to the control unit of the base station. The base station is a combination of sectors and a control unit. At the same time, a certain part of the settlement or territory is served by several base stations connected to a special unit at once - local zone controller(abbreviated LAC, Local Area Controller or just "controller"). As a rule, one controller unites up to 15 base stations of a certain area.

For their part, the controllers (there may also be several) are connected to the main unit - Mobile services control center (MSC, Mobile services Switching Center), which for ease of perception is called simply "commutator". The switch, in turn, provides input and output to any communication lines - both cellular and wired.

If you display what is written in the form of a diagram, you get the following:
Small-scale GSM networks (usually regional) can use just one switch. Large ones, such as our “big three” operators MTS, Beeline or MegaFon, serving millions of subscribers at the same time, use several MSC devices interconnected at once.

Let's see why such a complex system is needed and why it is impossible to connect the base station antennas to the switch directly? To do this, you need to talk about another term, called in technical language handover (handover). It characterizes handover in mobile networks according to the handover principle. In other words, when you move down the street on foot or in a vehicle and talk on the phone at the same time, so that your conversation is not interrupted, you should timely switch your device from one BS sector to another, from the coverage area of ​​​​one base station or controller local zone to another, etc. Therefore, if the base station sectors were connected directly to the switch, it would have to carry out this handover procedure for all its subscribers itself, and the switch already has enough tasks. Therefore, in order to reduce the probability of equipment failures associated with its overloads, the scheme for constructing GSM cellular networks is implemented according to a multi-level principle.

As a result, if you and your phone move from the service area of ​​one BS sector to the coverage area of ​​another, then this movement is carried out by the control unit of this base station, without touching the more “high-priced” devices - LAC and MSC. If the handover occurs between different BSs, then LAC is already taken for it, etc.

The switch is nothing more than the main "brain" of GSM networks, so its operation should be considered in more detail. The cellular network switch takes on approximately the same tasks as the PBX in the networks of wired operators. It is he who understands where you are making the call or who is calling you, regulates the work of additional services and, in fact, decides whether you can currently make your call or not.

Now let's see what happens when you turn on your phone or smartphone?

So, you pressed the "magic button" and your phone turned on. On the SIM card of your mobile operator there is a special number called IMSI - International Subscriber Identification Number (International Subscriber Identification Number). It is a unique number for each SIM-card not only for your operator MTS, Beeline, MegaFon, etc., but a unique number for all mobile networks in the world! It is on it that operators distinguish subscribers among themselves.

When you turn on the phone, your device sends this IMSI code to the base station, which transmits it further to the LAC, which, in turn, sends it to the switch. At the same time, two additional devices connected directly to the switch come into our game - HLR (Home Location Register) and VLR (Visitor Location Register). Translated into Russian, this is, respectively, Register of home subscribers and Register of guest subscribers. HLR stores the IMSI of all subscribers in its network. The VLR contains information about those subscribers who currently use the network of this operator.

The IMSI number is transmitted to the HLR using an encryption system (another device is responsible for this process AuC - Authentication Center). At the same time, HLR checks whether there is a subscriber with this number in its database, and if the fact of its presence is confirmed, the system looks at whether he can currently use communication services or, say, has a financial block. If everything is normal, then this subscriber goes to VLR and after that he gets the opportunity to call and use other communication services.

For clarity, we will display this procedure using a diagram:

Thus, we briefly described the principle of operation of GSM cellular networks. In fact, this description is rather superficial, because if we delve into the technical details in more detail, then the material would turn out to be many times more voluminous and much less understandable for most readers.

In the second part, we will continue our acquaintance with the operation of GSM networks and consider how and for what the operator debits funds from our account with you.

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 the description of the GSM standard beyond its scope.

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. Base station antennas are directed in 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 inside 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

Mobile cellular

cellular- one of the types of mobile radio communications, which is based on cellular network. The key feature is that the total coverage area is divided into cells (cells) determined by the coverage areas of individual base stations (BS). The cells partially overlap and together form a network. On an ideal (flat and undeveloped) surface, the coverage area of ​​one BS is a circle, so the network composed of them looks like honeycombs with hexagonal cells (honeycombs).

It is noteworthy that in the English version the connection is called "cellular" or "cellular" (cellular), which does not take into account the hexagonal cells.

The network consists of transceivers spaced apart in space operating in the same frequency range, and switching equipment that allows you to determine the current location of mobile subscribers and ensure communication continuity when a subscriber moves from the coverage area of ​​one transceiver to the coverage area of ​​another.

Story

The first use of mobile telephone radio in the United States dates back to 1921 when the Detroit police used one-way dispatch communication 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 on 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 had completely supplanted 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. 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, a Moscow engineer L. I. Kupriyanovich created a prototype of a wearable 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 apparatus, weighing 0.5 kg and the size of a cigarette box. In the 1960s, Christo Bochvarov demonstrated his prototype of a pocket mobile radiotelephone in Bulgaria. At the Interorgtekhnika-66 exhibition, Bulgaria presents a set for organizing local mobile communication from PAT-0.5 and ATRT-0.5 pocket mobile phones and a RATC-10 base station that connects 10 subscribers.

At the end of the 50s, the development of the Altai car radiotelephone system began in the USSR, 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 a 330 MHz band was allocated for it.

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

Of course, as is usually the case in life, individual 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 with manual channel switching by users in predetermined places. However, the architecture of the system that is today known as a cellular communication system was outlined only in a technical report by the Bell System company, submitted to the US Federal Communications Commission in December 1971. And from that time, the development of cellular communication proper began, which became truly triumphant from 1985 in the last ten plus years.

In 1974, the US Federal Communications Commission decided to allocate a 40 MHz frequency band for cellular communications in the 800 MHz band; in 1986 another 10 MHz was added to it in the same range. In 1978, Chicago began testing the first experimental cellular communication system for 2,000 subscribers. Therefore, 1978 can be considered the year of the beginning of the practical application of cellular communications. The first automatic commercial cellular communication system was also put into operation in Chicago in October 1983 by American Telephone and Telegraph (AT&T). Cellular communication has been used in Canada since 1978, in Japan since 1979, in the Scandinavian 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 the city, it reached 100% coverage of the territory of Finland in. The size of the cell was about 30 km, in the city it had more than 30 thousand subscribers. She worked at a frequency of 150 MHz.

The principle of operation of cellular communication

The main components of the cellular network are cell phones and base stations. Base stations are usually located on the roofs of buildings and towers. When turned on, the cell phone listens to the air, 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 go on an analog protocol (NMT-450) or digital (DAMPS, GSM, eng. handover).

Cellular networks can consist of base stations of different standards, which allows you to optimize the network and improve its coverage.

Cellular networks of different operators are connected to each other, as well as to the fixed 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 from different countries can enter into roaming agreements. Thanks to such contracts, the subscriber, while abroad, can make and receive calls through the network of another operator (though at higher rates).

Cellular communication in Russia

In Russia, cellular communication began to be introduced in 1990, commercial use began on September 9, 1991, when in St. Petersburg, Delta Telecom launched the first cellular network in Russia (it worked in the NMT-450 standard) and a symbolic cellular call by the mayor of St. Petersburg, Anatoly Sobchak. By July 1997, the total number of subscribers in Russia was about 300,000. For 2007, the main cellular communication protocols used in Russia are GSM-900 and GSM-1800. In addition, UMTS also works. In particular, the first fragment of the network of this standard in Russia was put into operation on October 2, 2007 in St. Petersburg by MegaFon. In the Sverdlovsk region, the DAMPS standard cellular communication network, owned by the Motiv Mobile Communications company, continues to operate.

In December 2008, there were 187.8 million mobile users in Russia (according to the number of SIM cards sold). The penetration rate of cellular communications (number of SIM-cards per 100 inhabitants) as of that date amounted to 129.4%. In the regions, excluding Moscow, the penetration rate exceeded 119.7%.

The market share of the largest cellular operators as of December 2008 was: 34.4% for MTS, 25.4% for VimpelCom and 23.0% for MegaFon.

In December 2007, the number of cellular communication users in Russia increased to 172.87 million subscribers, in Moscow - up to 29.9 million, in St. Petersburg - up to 9.7 million. The level of penetration in Russia - up to 119.1%, Moscow - 176% , St. Petersburg - 153%. 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 the data of 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 figure among the G8 countries.

Based on a study of the Russian cellular communications market, IDC concluded that in 2005 the total duration of conversations on a cell phone of the inhabitants of the Russian Federation reached 155 billion minutes, and 15 billion text messages were sent.

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.

see also

Sources

Links

• Information site about generations and standards of cellular communications.
• Cellular communications in Russia 2002-2007, official statistics