Mobile cellular communication. How GSM networks work

Do you know what happens after you have dialed a friend's number on your mobile phone? How does the cellular network find it in the mountains of Andalusia or on the coast of the distant Easter Island? Why is the conversation sometimes interrupted unexpectedly? Last week I visited the Beeline company and tried to figure out how the cellular communication works ...

A large area of ​​the populated part of our country is covered by Base Stations (BS). In the field, they look like red and white towers, but in the city they are hidden on the roofs of non-residential buildings. Each station picks up a signal from mobile phones at a distance of up to 35 kilometers and communicates with a mobile phone using service or voice channels.

After you have dialed a friend's number, your phone contacts the base station (BS) nearest to you via the service channel and asks to allocate a voice channel. The base station sends a request to the controller (BSC), and that forwards it to the switch (MSC). If your friend is a subscriber of the same cellular network, then the switch will check with the Home Location Register (HLR), find out where the called subscriber is currently located (at home, in Turkey or in Alaska), and will transfer the call to the appropriate switch, where he is from. will forward to the controller and then to the Base Station. The Base Station will connect to your mobile phone and connect you with a friend. If your friend is a subscriber of another network or you call a landline phone, then your switch will turn to the corresponding switch of the other network. Hard? Let's take a closer look. The Base Station is a pair of iron cabinets locked in a well-air-conditioned room. Considering that in Moscow it was +40 on the street, I wanted to live a little in this room. Usually, the Base Station is located either in the attic of a building or in a container on the roof:

2.

The Base Station antenna is divided into several sectors, each of which "shines" in its own direction. The vertical antenna communicates with telephones, the round antenna connects the Base Station with the controller:

3.

Each sector can handle up to 72 calls simultaneously, depending on setup and configuration. A Base Station can have 6 sectors, so one Base Station can handle up to 432 calls, however, there are usually fewer transmitters and sectors installed on the station. Cellular operators prefer to install more base stations to improve the quality of communication. The base station can operate in three bands: 900 MHz - the signal on this frequency travels further and better penetrates into buildings 1800 MHz - the signal travels over shorter distances, but allows you to install more transmitters on 1 sector of 2100 MHz - 3G network This is how the cabinet looks like with 3G equipment:

4.

900 MHz transmitters are installed at Base Stations in the fields and villages, and in the city, where the Base Stations are stuck like a hedgehog's needles, basically, communication is carried out at a frequency of 1800 MHz, although transmitters of all three bands can be present at any Base Station at the same time.

5.

6.

A 900 MHz signal can hit up to 35 kilometers, although the "range" of some Base Stations located along the routes can reach up to 70 kilometers, by reducing the number of simultaneously served subscribers at the station by half. Accordingly, our telephone, with its small built-in antenna, can also transmit signals up to 70 kilometers ... All Base Stations are designed to provide optimal radio coverage at ground level. Therefore, despite the range of 35 kilometers, the radio signal is simply not sent to the flight altitude of the aircraft. However, some airlines have already begun installing low-power base stations on their aircraft that provide coverage inside the aircraft. Such a BS connects to a terrestrial cellular network using a 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, such as turning off the voice on night flights. The phone can measure the signal strength from 32 Base Stations at the same time. It sends information about the top 6 (by signal strength) via the service channel, and the controller (BSC) decides which BS to transmit the current call (Handover) if you are on the move. Sometimes the phone can make a mistake and transfer you to the base station with the worst signal, in which case the conversation can be interrupted. It may also appear that all voice lines are busy at the Base Station that your phone has selected. In this case, the conversation will also be interrupted. They also told me about the so-called "upper floors problem." If you live in a penthouse, sometimes, when moving from one room to another, the conversation can be interrupted. This is because in one room the phone can "see" one BS, and in the second - the other, if it goes to the other side of the house, and, at the same time, these 2 Base Stations are located at a great distance from each other and are not registered as " neighboring "from the mobile operator. In this case, the transfer of a call from one BS to another will not occur:

Communication in the metro is provided in the same way as on the street: Base Station - controller - switch, with the only difference that small Base Stations are used there, and in the tunnel the coverage is provided not by an ordinary antenna, but by a special radiating cable. As I wrote above, one BS can make up to 432 calls simultaneously. Usually this power is enough for the eyes, but, for example, during some holidays, the BS may not cope with the number of people who want to call. This usually happens on New Years, when everyone starts congratulating each other. SMS are transmitted via service channels. On March 8 and February 23, people prefer to congratulate each other using SMS, sending funny rhymes, and the phones often cannot agree with the BS on the allocation of a voice channel. I was told an interesting case. From one district of Moscow, subscribers began to receive complaints that they could not get through to anywhere. The technicians began to figure it out. Most of the voice lines were free, and all service lines were busy. It turned out that next to this BS there was an institute where exams were being held and students were constantly exchanging text messages. The phone divides long SMS into several short ones and sends each one separately. The technical service staff advise sending such greetings using MMS. It will be faster and cheaper. From the Base Station, the call goes to the controller. It looks as boring as the BS itself - it's just a set of cabinets:

7.

Depending on the equipment, the controller can serve up to 60 Base Stations. Communication between the BS and the controller (BSC) can be carried out via a radio relay channel or via optics. The controller manages the operation of radio channels, incl. controls the movement of the subscriber, signal transmission from one BS to another. The switch looks much more interesting:

8.

9.

Each switch serves from 2 to 30 controllers. He already occupies a large hall, filled with various cabinets with equipment:

10.

11.

12.

The switch handles traffic management. Remember the old films, where people first dialed to the "girl", and then she already connected them with another subscriber, poking wires? Modern switches are also doing the same:

13.

To control the network, Beeline has several cars, which they affectionately call "hedgehogs". They move around the city and measure the signal strength of their own network, as well as the network level of colleagues from the Big Three:

14.

The entire roof of such a car is studded with antennas:

15.

Inside there is equipment that makes hundreds of calls and records information:

16.

Round-the-clock control over switches and controllers is carried out from the Flight Control Center of the Network Control Center (CCC):

17.

There are 3 main areas of control over the cellular network: accidents, statistics and feedback from subscribers. Just like in airplanes, all the equipment of the cellular network has sensors that send a signal to the CCS and output information to the dispatcher's computers. If some equipment is out of order, then the light on the monitor will start blinking. CCS also keeps track of statistics for all switches and controllers. He analyzes it by comparing it with previous periods (hour, day, week, etc.). If the statistics of any of the nodes began to differ sharply from the previous indicators, then the “light bulb” will start blinking on the monitor again. Subscriber service operators receive feedback. If they cannot solve the problem, then the call is forwarded to a technician. If he also turns out to be powerless, then an "incident" is created in the company, which is decided by the engineers involved in the operation of the corresponding equipment. The switches are monitored by 2 engineers around the clock:

18.

The graph shows the activity of Moscow switches. It is clearly seen that almost no one calls at night:

19.

Control over the controllers (sorry for the tautology) is carried out from the second floor of the Network Control Center:

22.

21.

How radio communication works

Radio (Latin radio - radiate, emit rays - radius - ray) is a type of wireless communication in which radio waves are used as a signal carrier, freely propagating in space.

Principle of operation
Transmission occurs as follows: on the transmitting side, a signal with the required characteristics (frequency and amplitude of the signal) is generated. The transmitted signal then modulates the higher frequency oscillation (carrier). The received modulated signal is emitted by the antenna into space. On the receiving side, radio waves induce a modulated signal in the antenna, after which it is demodulated (detected) and filtered by a low-pass filter (thereby getting rid of the high-frequency component - the carrier). The received modulated signal is radiated by the antenna into space.
On the receiving side, the radio waves induce a modulated signal in the antenna, after which it is demodulated (detected) and filtered by a low-pass filter (thereby getting rid of the high-frequency component - the carrier).). Thus, a useful signal is extracted. The received signal may differ slightly from that transmitted by the transmitter (distortion due to interference and interference).

Frequency bands
The frequency grid used in radio communications is conventionally divided into ranges:

• Long waves (LW) - f = 150-450 kHz (l = 2000-670 m)
• Medium waves (MW) - f = 500-1600 kHz (l = 600-190 m)
• Short waves (HF) - f = 3-30 MHz (l = 100-10 m)
• Ultrashort waves (VHF) - f = 30 MHz- 300 MHz (l = 10-1 m)
• High frequencies (HF-centimeter range) - f = 300 MHz - 3 GHz (l = 1-0.1 m)
• Extremely high frequencies (EHF-millimeter range) - f = 3 GHz - 30 GHz (l = 0.1-0.01 m)
• Hyperhigh frequencies (HHF - micrometer range) - f = 30 GHz - 300 GHz (l = 0.01-0.001 m)

Depending on the range, radio waves have their own characteristics and propagation laws:

• LWs are strongly absorbed by the ionosphere; surface waves, which propagate around the earth, are of primary importance. Their intensity decreases relatively quickly with distance from the transmitter.
• SW are strongly absorbed by the ionosphere during the day, and the area of ​​effect is determined by the surface wave, in the evening they are well reflected from the ionosphere and the area of ​​effect is determined by the reflected wave.
• HF propagates exclusively through reflection by the ionosphere, so there is a so-called radio silence zone around the transmitter. During the day, shorter waves (30 MHz) propagate better, at night, longer ones (3 MHz). Short waves can travel long distances with low transmitter power.
• VHF propagates in a straight line and, as a rule, is not reflected by the ionosphere. They easily bend around obstacles and have a high penetrating power.
• HF does not go around obstacles, spreads within the line of sight. Used in WiFi, cellular, etc.
• EHF does not bend around obstacles, is reflected by most of the obstacles, and spreads within the line of sight. Used for satellite communications.
• Hyper-high frequencies do not bend around obstacles, are reflected like light, and propagate within the line of sight. Limited use.

Propagation of radio waves
Radio waves propagate in emptiness and in the atmosphere; earthly solid and water are opaque for them. However, due to the effects of diffraction and reflection, communication is possible between points on the earth's surface that do not have a line of sight (in particular, those located at a great distance).
The propagation of radio waves from a source to a receiver can occur in several ways simultaneously. This spread is called multipath. Due to the multipath and changes in the parameters of the environment, fading occurs - a change in the level of the received signal over time. With multipath, the change in the signal level occurs due to interference, that is, at the point of reception, the electromagnetic field is the sum of time-shifted radio waves of the range.

Radar

Radar- the field of science and technology, combining methods and means of detection, measuring coordinates, as well as determining the properties and characteristics of various objects based on the use of radio waves. A close and somewhat overlapping term is radio navigation, however, in radio navigation, an object whose coordinates are measured plays a more active role, most often this is the determination of its own coordinates. The main technical device for radar is a radar station.

Distinguish between active, semi-active, active with a passive response and passive RL. They are subdivided according to the used range of radio waves, by the type of the probing signal, the number of channels used, the number and type of measured coordinates, the location of the radar.

Operating principle

Radar is based on the following physical phenomena:

• Radio waves are scattered by electrical inhomogeneities encountered along the path of their propagation (objects with other electrical properties that are different from the properties of the propagation medium). In this case, the reflected wave, as well as the actual radiation of the target, allows the target to be detected.
• At large distances from the radiation source, it can be assumed that radio waves propagate in a straight line and at a constant speed, due to which it is possible to measure the range and angular coordinates of the target (Deviations from these rules, which are valid only in the first approximation, are studied by a special branch of radio engineering - Radio wave propagation. these deviations lead to measurement errors).
• The frequency of the received signal differs from the frequency of the emitted oscillations with the mutual movement of the points of reception and radiation (Doppler effect), which allows you to measure the radial speeds of the target relative to the radar.
• Passive radar uses the emission of electromagnetic waves by the observed objects, it can be thermal radiation inherent in all objects, active radiation created by the technical means of the object, or spurious radiation created by any objects with working electrical devices.

cellular

cellular, mobile network- 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 honeycombs overlap partially and together form a network. On an ideal (even and without building) surface, the coverage area of ​​one BS is a circle, therefore, the network composed of them looks like honeycombs with hexagonal cells (honeycombs).

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

The principle of cellular communication

The main components of a cellular network are cell phones and base stations, which are usually located on rooftops and towers. When turned on, the cell phone listens to the air, finding a signal from the base station. The telephone then sends its unique identification code to the station. The telephone and the station maintain constant radio contact, periodically exchanging packets. The phone can communicate with the station using 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 of the service cell deteriorates), it establishes communication with another (eng. handover).

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

Cellular networks of different operators are 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 conclude roaming agreements with each other. Thanks to such agreements, the 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 done at higher rates. The possibility of roaming appeared only in 2G standards and is one of the main differences from 1G networks.

Operators can share network infrastructure, reducing network deployment and operational costs.

Cellular services

Cellular operators provide the following services:

• Voice call;
• Answering machine in cellular communication (service);
• Roaming;
• Caller ID (Automatic Caller ID) and AntiAON;
• Reception and transmission of short text messages (SMS);
• Reception and transmission of multimedia messages - images, melodies, video (MMS service);
• Mobile bank (service);
• Access to the Internet;
• Video call and video conferencing

TV

TV(Greek τήλε - far away and lat. video- I see; from Novolatinsky televisio- far-sightedness) - a set of devices for transmitting a moving image and sound over a distance. In common use, it is also used to designate organizations involved in the production and distribution of television programs.

Basic principles

Television is based on the principle of sequential transmission of picture elements by radio signal or by wire. The decomposition of the image into elements occurs using a Nipkov disk, a cathode-ray tube or a semiconductor matrix. The number of picture elements is selected in accordance with the radio channel bandwidth and physiological criteria. To narrow the band of transmitted frequencies and reduce the visibility of flickering on the TV screen, interlaced scanning is used. It also allows you to increase the smoothness of the transmission of motion.

The television path in general includes the following devices:

1. TV transmission camera. Serves for converting an image obtained with a lens on a target of a transmitting tube or semiconductor matrix into a television video signal.
2. Video recorder. Records and at the right time reproduces the video signal.
3. Video mixer. Allows you to switch between multiple image sources: camcorders, VCRs and others.
4. Transmitter. The RF signal is modulated by a television video signal and transmitted by radio or wire.
5. Receiver - TV. With the help of sync pulses contained in the video signal, the television image is reproduced on the receiver screen (kinescope, LCD, plasma panel).

In addition, an audio path similar to a radio transmission path is used to create a television transmission. Sound is transmitted on a separate frequency, usually using frequency modulation, a technique similar to FM radio stations. In digital television, soundtrack, often multichannel, is transmitted in a common data stream with an image.

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Date the page was created: 2016-04-11

Do you know what happens after you have dialed a friend's number on your mobile phone? How does the cellular network find it in the mountains of Andalusia or on the coast of the distant Easter Island? Why is the conversation sometimes interrupted unexpectedly? Last week I visited the Beeline company and tried to figure out how the cellular communication works ...

A large area of ​​the populated part of our country is covered by Base Stations (BS). In the field, they look like red and white towers, but in the city they are hidden on the roofs of non-residential buildings. Each station picks up a signal from mobile phones at a distance of up to 35 kilometers and communicates with a mobile phone using service or voice channels.

After you have dialed a friend's number, your phone contacts the base station (BS) nearest to you via the service channel and asks to allocate a voice channel. The base station sends a request to the controller (BSC), and that forwards it to the switch (MSC). If your friend is a subscriber of the same cellular network, then the switch will check with the Home Location Register (HLR), find out where the called subscriber is currently located (at home, in Turkey or in Alaska), and will transfer the call to the appropriate switch, where he is from. will forward to the controller and then to the Base Station. The Base Station will connect to your mobile phone and connect you with a friend. If your friend is a subscriber of another network or you call a landline phone, then your switch will turn to the corresponding switch of the other network.

Hard? Let's take a closer look.

The Base Station is a pair of iron cabinets locked in a well-air-conditioned room. Considering that in Moscow it was +40 on the street, I wanted to live a little in this room. Usually, the Base Station is located either in the attic of a building or in a container on the roof:

2.

The Base Station antenna is divided into several sectors, each of which "shines" in its own direction. The vertical antenna communicates with telephones, the round antenna connects the Base Station with the controller:

3.

Each sector can handle up to 72 calls simultaneously, depending on setup and configuration. A Base Station can have 6 sectors, so one Base Station can handle up to 432 calls, however, there are usually fewer transmitters and sectors installed on the station. Cellular operators prefer to install more base stations to improve the quality of communication.

The base station can operate in three bands:

900 MHz - the signal at this frequency travels further and better penetrates into buildings
1800 MHz - the signal spreads over shorter distances, but allows you to install more transmitters per sector
2100 MHz - 3G network

This is how a closet with 3G equipment looks like:

4.

900 MHz transmitters are installed at Base Stations in the fields and villages, and in the city, where the Base Stations are stuck like a hedgehog's needles, basically, communication is carried out at a frequency of 1800 MHz, although transmitters of all three bands can be present at any Base Station at the same time.

5.

6.

A 900 MHz signal can hit up to 35 kilometers, although the "range" of some Base Stations located along the routes can reach up to 70 kilometers, by reducing the number of simultaneously served subscribers at the station by half. Accordingly, our phone, with its small built-in antenna, can also transmit a signal over a distance of up to 70 kilometers ...

All Base Stations are designed to provide optimum RF coverage at ground level. Therefore, despite the range of 35 kilometers, the radio signal is simply not sent to the flight altitude of the aircraft. However, some airlines have already begun installing low-power base stations on their aircraft that provide coverage inside the aircraft. Such a BS connects to a terrestrial cellular network using a 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, such as turning off the voice on night flights.

The phone can measure the signal strength from 32 Base Stations at the same time. It sends information about the top 6 (by signal strength) via the service channel, and the controller (BSC) decides which BS to transmit the current call (Handover) if you are on the move. Sometimes the phone can make a mistake and transfer you to the base station with the worst signal, in which case the conversation can be interrupted. It may also appear that all voice lines are busy at the Base Station that your phone has selected. In this case, the conversation will also be interrupted.

I was also told about the so-called "upper floors problem". If you live in a penthouse, sometimes, when moving from one room to another, the conversation can be interrupted. This is because in one room the phone can "see" one BS, and in the second - another, if it goes to the other side of the house, and, at the same time, these 2 Base Stations are located at a great distance from each other and are not registered as " neighboring "at the cellular operator. In this case, the transfer of a call from one BS to another will not occur:

Communication in the metro is provided in the same way as on the street: Base Station - controller - switch, with the only difference that small Base Stations are used there, and in the tunnel the coverage is provided not by an ordinary antenna, but by a special radiating cable.

As I wrote above, one BS can make up to 432 calls simultaneously. Usually this power is enough for the eyes, but, for example, during some holidays, the BS may not cope with the number of people who want to call. This usually happens on New Years, when everyone starts congratulating each other.

SMS are transmitted via service channels. On March 8 and February 23, people prefer to congratulate each other using SMS, sending funny rhymes, and the phones often cannot agree with the BS on the allocation of a voice channel.

I was told an interesting case. From one district of Moscow, subscribers began to receive complaints that they could not get through to anywhere. The technicians began to figure it out. Most of the voice lines were free, and all service lines were busy. It turned out that next to this BS there was an institute where exams were being held and students were constantly exchanging text messages.

The phone divides long SMS into several short ones and sends each one separately. The technical service staff advise sending such greetings using MMS. It will be faster and cheaper.

From the Base Station, the call goes to the controller. It looks as boring as the BS itself - it's just a set of cabinets:

7.

Depending on the equipment, the controller can serve up to 60 Base Stations. Communication between the BS and the controller (BSC) can be carried out via a radio relay channel or via optics. The controller manages the operation of radio channels, incl. controls the movement of the subscriber, signal transmission from one BS to another.

The switch looks much more interesting:

8.

9.

Each switch serves from 2 to 30 controllers. He already occupies a large hall, filled with various cabinets with equipment:

10.

11.

12.

The switch handles traffic management. Remember the old films, where people first dialed up to the "girl", and then she was already connecting them to another subscriber, poking wires? Modern switches are also doing the same:

13.

To control the network, Beeline has several cars, which they affectionately call "hedgehogs". They move around the city and measure the signal strength of their own network, as well as the network level of colleagues from the Big Three:

14.

The entire roof of such a car is studded with antennas:

15.

Inside there is equipment that makes hundreds of calls and records information:

16.

Round-the-clock control over switches and controllers is carried out from the Flight Control Center of the Network Control Center (CCC):

17.

There are 3 main areas of control over the cellular network: accidents, statistics and feedback from subscribers.

Just like in airplanes, all the equipment of the cellular network has sensors that send a signal to the CCS and output information to the dispatcher's computers. If some equipment is out of order, then the light on the monitor will start flashing.

CCS also keeps track of statistics for all switches and controllers. He analyzes it by comparing it with previous periods (hour, day, week, etc.). If the statistics of any of the nodes began to differ sharply from the previous indicators, then the light on the monitor will start blinking again.

Subscriber service operators receive feedback. If they cannot solve the problem, then the call is forwarded to a technician. If he also turns out to be powerless, then an "incident" is created in the company, which is decided by the engineers involved in the operation of the corresponding equipment.

The switches are monitored by 2 engineers around the clock:

18.

The graph shows the activity of Moscow switches. It is clearly seen that almost no one calls at night:

19.

Control over the controllers (sorry for the tautology) is carried out from the second floor of the Network Control Center:

22.

21.

I understand that you still have a bunch of questions about how the cellular network works. The topic is complex, and I asked a specialist from Beeline to help me respond to your comments. The only request is to stick to the theme. And questions like "Beeline radishes. They stole 3 rubles from my account" - address the subscriber service 0611.

Tomorrow there will be a post about how a whale jumped in front of me, but I did not have time to photograph it. Stay Tuned!

Communication is called mobile if the source of information or its recipient (or both) move in space. Since its inception, radio communication has been mobile. Above, in the third chapter, it is shown that the first radio stations were intended for communication with mobile 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, lost in the ice of the Baltic Sea, was saved. However, in those years, this "mobile communication" required bulky radio transceiver devices, which did not contribute to the development of the much-needed individual radio communication even in the Armed Forces, let alone private clients.

On June 17, 1946, in St. Louis, USA, telephone business leaders AT&T and Southwestern Bell launch the first private radiotelephone network. The elementary base of the equipment was tube electronic devices, so the equipment was very bulky and was 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 dimensions. 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 deteriorated the quality of communication. To eliminate mutual interference at repeating frequencies, it was necessary to ensure a minimum of a hundred-kilometer spacing in space between the two groups of radio systems. That is why mobile communications were basically used for the needs of special services. For mass implementation, it was required to change not only the weight and dimensions, but also the very principle of organizing communications.

As noted above, in 1947, the transistor was invented, performing the functions of vacuum tubes, but having a much smaller size. It was the appearance of transistors that was of great importance for the further development of radiotelephone communication. The replacement of electronic tubes with transistors has created the prerequisites for the widespread introduction of a mobile phone. The main deterrent was the principle of communication organization, which would eliminate or at least reduce the influence of mutual interference.

Studies of the ultrashort wavelength range of waves, carried out in the 40s of the last century, made it possible to reveal its main advantage over short waves - broadband, i.e. high frequency capacity and the main disadvantage - strong absorption of radio waves by the propagation medium. Radio waves of this range are not able to bend around the earth's surface, therefore, 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 disadvantage soon turned into an advantage that gave impetus to the active mass adoption of cellular telephony.

In 1947, D. Ring, an employee of the American company Bell Laboratories, proposed a new idea for organizing communications. It consisted in dividing space (territory) into small sections - cells (or cells) with a radius of 1–5 kilometers and in separating radio communication within one cell (by rational repetition of the communication frequencies used) from communication between cells. Frequency repetition has significantly reduced frequency resource utilization problems. 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 locate a base transmitting and receiving radio station, which provided radio communication within the cell with all subscribers. The dimensions of the cell were determined by the maximum communication range of the radiotelephone apparatus with the base station. This maximum range is called the cell radius. During the conversation, the cellular radiotelephone is connected to the base station by a radio channel, through which the telephone conversation is transmitted. Each subscriber must have his own micro-radio station - "mobile phone" - a combination of a telephone, a transceiver and a mini-computer. Subscribers communicate with each other through base stations that are connected to each other and to the public telephone network.

To ensure uninterrupted communication when a subscriber moves 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 quickly that the subscriber simply does not notice it. Thus, computers are the central part of a mobile communication system. They search for a subscriber 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 the "foreign" cellular network to "their" network. This happens at the moment when the “stranger” subscriber is in the coverage area of ​​the new base station. Thus, roaming is carried out (which in English means "wandering" or "vagrancy").

As noted above, the principles of modern mobile communications were an achievement already at the end of the 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 application of cellular communication became possible only after the invention of microprocessors and integrated semiconductor microcircuits.

The first cellular telephone was designed by Martin Cooper (Motorola, USA).

In 1973, in New York, on top of a 50-storey 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 land lines.

On April 3, 1973, Martin Cooper dialed his boss's number and said the following words: “Imagine, Joel, that I call you from the world's first cell phone. I have it in my hands, and I am walking along New York Street. "

The phone Martin called from was called Dyna-Tac. Its dimensions were 225 × 125 × 375 mm, and its weight was a little less than 1.15 kg, which, however, is much less than the 30 kilogram devices of the late forties. With the help of the device it was possible to call and receive a signal, to negotiate with a subscriber. This phone had 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. The Dyna-Tac batteries allowed a talk time of about half an hour, and it took 10 hours to charge them.

Although most of the development took place 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 range served 250 subscribers.

A little later, cellular communication began its triumphant march around the world. More and more countries understood the benefits and convenience that it could bring. However, the lack of a single international standard for using 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 major deficiency, since the late seventies Sweden, Finland, Iceland, Denmark and Norway have started joint research to develop a single standard. The result of the research was the NMT-450 (Nordic Mobile Telephone) communication standard, which was intended to operate in the 450 MHz range. This standard was first used in 1981 in Saudi Arabia, and only a month later in Europe. Various versions of the NMT-450 were adopted in Austria, Switzerland, Holland, Belgium, Southeast Asia and the Middle East.

In 1983, the AMPS (Advanced Mobile Phone Service) network was launched in Chicago, 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 and began using its own Radiocom-2000 standard since 1985.

The next was the NMT-900 standard, using the frequencies of the 900 MHz range. The new version was introduced in 1986. It allowed to increase the number of subscribers and improve the stability of the system.

However, all of 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 (PM) modulation - as in conventional radio stations. This method has a number of significant disadvantages, the main of which are the ability to listen to conversations by other subscribers and the impossibility of combating signal fading when the subscriber moves, as well as under the influence of the terrain and buildings. The congestion of the frequency ranges caused interference in 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 Administrations of Posts and Telecommunications (CEPT), uniting 26 countries, decided to create a special group, Groupe Special Mobile. Its goal was to develop a single European standard for digital cellular communications. The new communication standard took eight years to develop, and was first announced only in 1990, when the specifications of the standard were proposed. The special group initially decided to use the 900 MHz band as a single standard, 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 was named 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 multiplexing (TDMA - time division multiple access, message encryption, block coding, and GMSK modulation) (Gaussian Minimum Shift Keying).

The first state to launch a GSM network is Finland, which launched this standard into commercial operation in 1992. The following year, the first DCS-1800 One-2-One network was launched in the UK. From that moment on, the global spread of the GSM standard all over the world begins.

The next step after GSM is the CDMA standard, which provides faster and more reliable communication due to the use of code division. This standard began to emerge in the United States in 1990. In 1993, the United States began to use CDMA (or IS-95) in the 800 MHz frequency range. At the same time, the DCS-1800 One-2-One network was launched in England.

In general, there were many communication standards, and by the mid-nineties most of the civilized countries were smoothly moving to digital specifications. If the networks of the first generation allowed only voice to be transmitted, then the second generation of cellular communication systems, which is GSM, also allow providing other non-voice services. In addition to the SMS service, the first GSM phones allowed for the transmission of other non-voice data. For this, a data transfer protocol was developed, called CSD (Circuit Switched Data). However, this standard had very modest characteristics - the maximum data transfer rate was only 9600 bits per second, and then on condition of stable communication. However, such speeds were quite enough for the transmission of a facsimile message.

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 meet the needs of their customers for access to the Internet, engineers invent the WAP protocol. WAP is an abbreviation for Wireless Application Protocol, which translates to wireless application access protocol. In principle, WAP can be called a simplified version of the standard Internet protocol HTTP, only adapted for the limited resources of mobile phones, such as small display sizes, low performance of telephone processors and low data transfer rates in mobile networks. However, this protocol did not allow standard Internet pages to be viewed; they had to be written in WML, 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 downloading or viewing the page, the communication channel is busy, and the same money is debited from the 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, the HSCSD (High-Speed ​​Circuit Switched Data) technology was born, which provided a quite acceptable speed - up to 43 kilobits per second. This technology was popular with a certain circle of users. But still, this technology did not lose the main drawback of its predecessor - data was still transmitted via a 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) appeared - 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 amount of transmitted and received data. In addition, GPRS has another advantage over earlier technologies for mobile data transmission - during the GPRS connection, the phone is still able to receive calls and SMS messages. At the moment, modern phone models on the market, when making a call, suspend the GPRS connection, which is automatically resumed at the end of the call. Such devices are classified as a class B GPRS terminal. It is planned to produce class A terminals, which will simultaneously download data and conduct 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. In theory, 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 cell phones on the market that support higher speeds.

With the advent of GPRS, they again remembered the WAP protocol, since now, with the help of new technology, access to small-volume WAP-pages becomes many times cheaper than in the days of CSD and HSCSD. Moreover, many telecom operators provide unlimited access to WAP-resources of the network for a small monthly subscription 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, the cell phone, computer and the Internet are merging. Developers and operators are offering us more and more different value-added services.
So, using the capabilities of GPRS, a new messaging format was created, which was called MMS (Multimedia Messaging Service), which, unlike SMS, allows you to send from a cell phone not only text, but also various multimedia information, for example, sound recordings, photos and even video clips. Moreover, an MMS message can be sent either to another phone that supports this format, or to an e-mail box.
The increase in the processor power of phones now allows you to download and run various programs on it. The Java2ME language is most often used to write them. Owners of most modern phones now have no difficulty connecting to the Java2ME application developers site and downloading to their phone, for example, a new game or other necessary program. Also, no one will be surprised by the possibility of connecting the phone to a personal computer in order to save or edit an address book or organizer on a PC using special software, most often supplied with the handset; while on the road, using a combination of mobile phone + laptop, go to the full-fledged Internet and view your e-mail. However, our needs are constantly growing, the volume of transmitted information is growing almost daily. And more and more demands are being made on cell phones, as a result of which the resources of current technologies are becoming insufficient to meet our growing demands.

It is for the solution of these requests that the rather recently created third-generation 3G networks are intended, in which data transmission dominates over voice services. 3G is not a communication standard, but the general name for all high-speed cellular networks that will grow and are already growing out of the existing ones. Huge data transfer rates 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 communication (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 are unlikely to be able to tell about how this evolutionary development will end.

Globally, there are now about 2 billion mobile phones in use, of which more than two-thirds are connected to the GSM standard. CDMA is the second most popular, while the rest represent specific standards used mainly in Asia. Now in developed countries there is a situation of "satiety", when demand stops growing.

Mobile cellular communication

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 honeycombs overlap partially and together form a network. On an ideal (even and without building) surface, the coverage area of ​​one BS is a circle, therefore, the network composed of them looks like honeycombs with hexagonal cells (honeycombs).

It is noteworthy that in the English version the communication is called "cellular" or "cellular" (cellular), which does not take into account the hexagonal nature of the honeycomb.

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

History

The first use of mobile telephony in the United States dates back to 1921: Detroit police used one-way dispatch in the 2 MHz band to transmit information from a central transmitter to vehicle-mounted receivers. In 1933, the New York police 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 completely replaced amplitude modulation. The first public mobile radiotelephone appeared in 1946 (St. Louis, USA; Bell Telephone Laboratories) using the 150 MHz band. In 1955, an 11-channel system began operating in the 150 MHz range, and in 1956 - a 12-channel system in the 450 MHz range. 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 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 apparatus weighing 0.5 kg and the size of a cigarette box. In the 60s Hristo Bochvarov in Bulgaria demonstrates his prototype of a pocket mobile radiotelephone. At the Interorgtechnika-66 exhibition, Bulgaria presents a set for organizing local mobile communications from pocket mobile phones RAT-0.5 and ATRT-0.5 and a base station RATTs-10, which provides connection of 10 subscribers.

At the end of the 50s, the development of the Altai automobile 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 has developed in other countries. Thus, in Norway, public telephone radio communications have been used as maritime mobile communications since 1931; in 1955 there were 27 coastal radio stations in the country. Terrestrial mobile communications began to develop after the Second World War in the form of hand-switched private 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 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 cellular system.

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 at predetermined locations. However, the architecture of the system that is today known as the cellular communication system was only outlined in the Bell System technical report submitted to the US Federal Communications Commission in December 1971. And from that time the development of cellular communication itself begins, which has become truly triumphant since 1985. g., in the last ten years and a little.

In 1974, the FCC decided to allocate a 40 MHz frequency band for cellular communications in the 800 MHz range; in 1986, another 10 MHz was added to it in the same range. In 1978, tests of the first prototype cellular communication system for 2,000 subscribers began in Chicago. Therefore, 1978 can be considered the year of the beginning of the practical application of cellular communications. The first automatic commercial cellular system was also commissioned in Chicago in October 1983 by American Telephone and Telegraph (AT&T). In Canada, cellular communication has been used 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 g. cellular communication operated in more than 140 countries of 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 has reached 100% coverage of the territory of Finland c. The cell size was about 30 km, and in the city there were more than 30 thousand subscribers. She worked at a frequency of 150 MHz.

The principle of cellular communication

The main components of a cellular network are cell phones and base stations... Base stations are usually located on rooftops and towers. When turned on, the cell phone listens to the air, finding a signal from the base station. The telephone then sends its unique identification code to the station. The telephone and the station maintain constant radio contact, periodically exchanging packets. The phone can communicate with the station using 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 network performance and improve its coverage.

Cellular networks of different operators are 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 from different countries can conclude roaming agreements. Thanks to such agreements, a subscriber, while abroad, can make and receive calls through the network of another operator (albeit 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 the first cellular network in Russia was launched in St. Petersburg by Delta Telecom (it worked in the NMT-450 standard) and the first a symbolic call by the mayor of St. Petersburg, Anatoly Sobchak. By July 1997, the total number of subscribers in Russia was about 300 thousand. For 2007, the main cellular communication protocols used in Russia are GSM-900 and GSM-1800. In addition, UMTS 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 the MegaFon company. The Sverdlovsk Region continues to operate a DAMPS cellular network owned by the MOTIV Cellular Communications Company.

In December 2008, there were 187.8 million mobile users in Russia (based on the number of SIM cards sold). The penetration rate of cellular communications (the number of SIM-cards per 100 inhabitants) as of this 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 mobile 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 penetration rate in Russia - up to 119.1%, in 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 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.

IDC, based on a study of the Russian cellular market, concluded that in 2005 the total duration of conversations on a cell phone of residents 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 of

Links

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