What kind of cellular communication. See what "cellular communication" is in other dictionaries

CELLULAR COMMUNICATION CELLULAR COMMUNICATION

CELLULAR COMMUNICATIONS (English cellular phone, mobile radio relay), view radiotelephony where the end devices are mobile phones (cm. MOBILE PHONE)- connected to each other using a cellular network - a set of special transceivers (base stations). Base stations communicate with each other using fixed communication channels, and with served mobile phones using radio waves. The area where mobile phones served by a separate base station can be located is called a cell (cell). One cellular telephone it is usually seen by several base stations at a time, and, according to the standards and protocols used in the cellular network, communicates with the base station that has the least signal attenuation (and this station does not have exhausted the limit on the number of telephones served). Thus, when a mobile phone moves with the person using it, and falls into the field of visibility of different base stations, then its connection to the cellular network is not broken, and it can make and receive calls, as well as use all the services of the cellular network.
Companies that provide access to cellular networks are called operators cellular.
The power of the radio transmitter of a mobile phone in the cellular network is much less (hundreds of times) than the power of the transmitter base station, therefore, mobile phones have relatively little big sizes and safe to use. Radiation level mobile phones governed by special international standards security. There are many standards and technologies for mobile communications.
First generation mobile networks
The first cellular networks were built using analog standards - first generation (1G) standards. The most common ones are NMT and AMPS. Usually, next to the name of the standard, they write down the frequency in megahertz, next to which the frequency range for the interaction of the base station with mobile phones, for example, base stations of NMT-450 networks communicate with cell phones at a frequency of 450 MHz.
A network based on the NMT (Nordic Mobile Telephone) standard, the first cellular communication standard, began operating in the Nordic countries in 1981. Also, NMT was the first mobile communication standard used in Russia (1991) and in the United States.
In analog standards to ensure simultaneous work several mobile phones in one cell, as well as base stations of different cells, only frequency division multiplexing (FDMA, Frequency Division Multiple Access, simultaneous access with frequency division) was used, which in conditions of a shortage of free frequencies means working in one cell a maximum of only 10 -20 telephones and large cell sizes. This was only acceptable given the relatively low prevalence of mobile communications. Also analog standards did not give any protection against interference, and sometimes it was possible to eavesdrop on the conversation with the help of a simple radio receiver.
In the 2000s. everywhere in the world, first-generation networks are being supplanted by second- and third-generation networks.
Second generation mobile networks
In networks of the second generation (2G, second generation), data between base stations and mobile phones is transmitted to digital form... This made it possible to use time division multiplexing (TDMA, Time Division Multiple Access, simultaneous access with time division) in the DAMPS standards and the GSM that replaced it for simultaneous operation from one base station of several phones - each frequency channel it is divided into several so-called "timeslots", that is, time intervals during which the channel is occupied by one telephone. Thus, one base station can serve up to several hundred phones at the same time. And the transmitter powers in second generation mobile phones have been reduced, since the transmission loss of digitized sound is much lower.
V CDMA standard(Code Division Multiple Access) are used by more than sophisticated methods division of radio air between different mobile phones. Moreover, no matter how much different phones in a cell, and no matter how many base stations there are neighbors, each mobile phone uses for reception and transmission the whole frequency band (channel) of a relatively large width - 1.25 MHz in the CDMA2000 1x standard. To distinguish signals from different telephones and base stations, each transmitter has its own code, which spreads over the entire channel width.
The most popular cellular standard is the second generation GSM - Global System for Mobile Communications (Global System for Mobile Communications). Mobile phones of this standard are now used by more than a billion people all over the world.
Data transmission technologies in second generation networks
But the main consequence of the transition to digital form signal, it became possible to use mobile phones to transmit not only voice (sound), but also other types of information. The first such service that made possible transfer text between mobile phones, was the so-called "service short messages» - Short message Service (abbreviated as SMS). SMS first appeared in the GSM standard (in December 1992, an experiment was carried out on the network of the British operator Vodaphone to sending SMS), but was later implemented in networks based on other standards. With the help of SMS technology, you can send not only short text messages, but also simple pictures and sounds, as well as express your emotions using special images - emoticons (from smile - smile). For this, EMS and Nokia Smart Messaging technologies are used.
Later, with the improvement of mobile phones and the development of computerization, technologies were introduced in GSM networks for the transmission of computer data, access to the Internet. (cm. THE INTERNET)... The first such technology was CSD (Circuit Switched Data, data transmission via direct connection), in which the timeslot allocated to the phone is used to transfer data at a speed of 9.6 kilobits per second - the timeslot is allocated in the same way as when making phone calls. In this case, the phone cannot be used for its intended purpose. To increase the transmission speed, the technology HSCSD (High Speed ​​CSD, high-speed CSD) was created - the phone receives several timeslots at once, and a special algorithm is used to correct errors depending on the quality of the connection. With this technology, the cell may not have enough timeslots for all mobile phones, so it has not become common.
The most common data transmission technology is GPRS (General Packet Radio Service). common use), which allows several mobile phones to use dedicated timeslots at once, uses different algorithms for different quality communication with the BS, different workload of the BS. Each phone uses a different number of timeslots, freeing them when not needed or requesting new ones. Timeslots are split between phones using batch splitting, as in computer networks... The number of timeslots that a phone can use is limited by hardware and depends on the class GPRS mobile phone. The transmission speed is asymmetric - if a class phone can use up to 4 timeslots to receive information with the 8th and 10th GPRS classes, then for transmission there are only 1-2. Theoretical limit speed for GPRS with an ideal connection (21.4 kilobits per second) and 5 allocated timeslots is 107 kilobits per second. But in reality, the average speed of GPRS is at the level of 56 kilobits per second. When using GPRS technology, mobile phones are assigned IP addresses on the Internet, which in most cases are not unique.
Further development of GPRS technology was EDGE technology (Enhanced Data Rates for GSM Evolution, increased speed data transmission for the development of GSM). In this technology, in comparison with GPRS, new information coding schemes have been applied, and the error handling algorithm has also been changed (erroneously transmitted packets are not transmitted again, only information for their recovery is transmitted). As a result, maximum speed transmission reaches 384 kilobits per second.
Sometimes GPRS technology is called "generation 2.5" - 2.5G mobile communication technology, and EDGE technology is called 2.75G technology.
For CDMA2000 networks, 1xRTT technology has been created, which allows reaching a speed of 144 kilobits per second.
Purpose of data transmission technologies in mobile networks
Initially, these technologies were used in mobile phones to access the Internet using personal computers, and only then, with further development mobile phones, provided Internet access directly from a mobile phone. To receive information on a mobile phone, WAP technology (Wireless Application Protocol, a protocol for wireless applications), which had relatively small requirements for technical specifications mobile phone. Pages were created on special language WML (Wireless Markup Language) adapted to the peculiarities of mobile phones - small size screen, only keyboard control, low data rates, delays in loading pages, and so on. Moreover, due to the low performance of the processor and the small memory size of the mobile phone, for maximum ease of operation mobile browser pages in this language were not processed directly, but with the help of an intermediate server (the so-called WAP-gateway), which compiled them into a special byte-code executed by a mobile phone. It is for this - the work of an intermediate server - mobile operators rate this service so highly.
However, with the advancement of mobile phones, changes soon took place. Firstly, the need for an intermediate server has disappeared - now the browsers of modern mobile phones do its work independently. Secondly, the specialized language WML is being replaced by the xHTML standard - it differs from the one commonly used on the Internet. HTML language only by adhering to some special rules, namely the XML specification. Thirdly, modern mobile phones have a sufficient screen size for displaying ordinary Internet pages intended for computers. Fourth, with development modern internet it turned out that the code of HTML-pages began to be simplified and structured, due to the fact that now it is written mainly by machine. Due to these changes, many modern phones are quite capable of handling HTML on their own.
Based on these data transmission technologies, additional services for mobile phones - for example, MMS (Multimedia Messaging System) multimedia messaging). Using a mobile phone, you can now easily compose a message containing text, image, sound, video or others computer files... Many MMS elements can be combined into slides, and the recipient MMS phone can show a presentation consisting of them. Technically, when an MMS message is sent, a dedicated data transfer protocol is used over a regular Internet connection such as GPRS.
MMS messages from a mobile phone can be sent not only to other mobile phones, but also to addresses Email- on e-mail all the files that make up the MMS will come. Each message can be sent to several addresses at once.
If the addressee is the number of another mobile phone that supports MMS, then he directly downloads the content of the message using a special protocol, either automatically or by special request... And if the receiving mobile phone does not support MMS, then it receives an SMS message containing a link on the Internet, by clicking on which you can view the MMS content via the Web either from the mobile phone itself or from a personal computer.
However, the majority of modern mobile phones are equipped with programs - e-mail clients, and as they improve, MMS becomes unnecessary and supplanted by other services, for example, BlackBerry.
Internet access from mobile phones can be used for the same purposes as in personal computers for example to use various services messaging like ICQ.
Third generation mobile communications
Data transmission rates in second-generation networks are insufficient for the implementation of many new tasks of mobile communication, in particular, the transmission of high-quality video in real time (videophone), modern photorealistic computer games via the Internet and others. To ensure the required speeds, new standards and protocols have been created:
1. UMTS standard (Universal Mobile Telecommunications System, universal system mobile communications) based on W-CDMA technologies(Wideband Code Division Multiple Access, wideband CDMA), partially compatible with GSM. The speed of data reception and transmission reaches 1920 kilobits per second.
2. 1xEV technology (evolution, development) for CDMA2000 networks. The data reception speed reaches 3.1 megabits per second, and the transmission speed reaches 1.8 megabits per second.
3. Technologies TD-SCMA, HSDPA and HSUPA. Allows you to achieve even more high speeds... As of 2006, W-CDMA technologies often provide HSDPA support. TD-SCMA under development.
Thus, modern technologies mobile communications are not so much mobile telephony technologies as universal information transfer technologies.

encyclopedic Dictionary. 2009 .

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In this article we will tell you about the history of the emergence of mobile communications

The first radiotelephone communication system appeared in 1946 in the USA - St. Louis. Radiotelephones operated on fixed frequencies and were manually switched. In the Soviet Union radio telephone communications appeared in 1959 and was called the "Altai" system. Naturally, it was not publicly available, but was used as a government connection and special services. In 1990-1994, during the collapse of the USSR, from the Soviet research institutes, a large mass of classified developments, including the development of multi-frequency, multi-base radiotelephone communications, were taken out of the cordon “for free”. And in 1991 in the USA, and later in Russian Federation appeared new standard radiotelephone - cellular communication NMT-450 ("Sotel"). Used analog signal... Later appeared digital standards- GSM-900 and GSM-1800.

With the progressive development of cellular communications, mobile telephones have become widely available. As a rule, a mobile telephone (hereinafter MTA) can operate at a distance of up to 1500 m from the base station.

As you know, everyone cell phone assigned its own electronic serial number(ESN), which is encoded in the microchip of the phone when the phone is manufactured. By activating the SIM-card (Subscriber Identity Module) - a microchip in which it is "flashed" subscriber number, the mobile phone receives a mobile an identification number(MIN).

Area covered GSM network(Global System for Mobile communications, - global system mobile communication), is divided into separate adjacent cells (cells) - hence the name "cellular communication", in the center of which there are transceiver base stations. Typically, such a station has six transmitters, which are located with a 120 ° radiation pattern and provide an even coverage of the area. One medium modern station can simultaneously serve up to 1000 channels. The area of ​​the "honeycomb" in the city is about 0.5-1 km 2, outside the city, depending on the geographical location, it can reach both 20 and 50 km 2. The telephone exchange in each "cell" is controlled by the base station, which receives and transmits signals in a wide range of radio frequencies (dedicated channel - the step for each cell phone is minimal). The base station is connected to a wired telephone network and equipped with equipment for converting the high-frequency signal of a cell phone into a low-frequency signal wired telephone and vice versa, which ensures the conjugation of these two systems. Technically modern equipment of the base station occupies an area of ​​1 ... 3 m 2 and is located within one small room, where its work is carried out in automatic mode... For stable work such a station only needs wired communication with a telephone exchange (PBX) and mains supply 220 V.

In cities and settlements with a large congestion of houses, base station transmitters are located right on the rooftops. In the suburbs and in open areas, towers are used in several sections (they can often be seen located along the highway).

The coverage area of ​​neighboring stations is contiguous. When moving telephone set its periodic registration takes place between the coverage areas of neighboring stations. Periodically, with an interval of 10 ... 60 minutes (depending on the operator), the base station emits a service signal. Having received it, the mobile phone automatically adds its MIN and ESN numbers to it and transmits the resulting code combination to the base station. Thus, the identification of a specific mobile cellular telephone, the account number of its owner and the binding of the device to specific area in which he is in this moment time. This moment is very important - already at this stage it is possible to control the movement of this or that object, and who benefits from it, the question is different - the main thing is there is an opportunity ...

When a user connects with someone on his phone, the base station assigns him one of the free frequencies of the zone in which he is located, makes the appropriate changes to his account (deducts funds) and transfers his call to the destination.

If mobile user during a conversation moves from one communication zone to another, the base station of the leaving zone (cell) automatically transfers the communication signal to free frequency the adjacent zone (honeycomb).

The most vulnerable from the point of view of the possibility of interception of ongoing negotiations (wiretapping) are analog mobile cell phones. In our region (St. Petersburg), such a standard was present until recently - this is the NMT450 standard (it is also present in the Republic of Belarus). Confident communication and its distance from the base station in such systems directly depend on the radiation power of the transmitting cell phone.

The analog principle of information transmission is based on the emission of a non-digital radio signal into the air, therefore, having tuned in to the corresponding frequency of such a communication channel, it is theoretically possible to listen to the conversation. However, it is worth "to cool especially hot heads" - to listen to cellular communications of this standard not so easy, since they are encrypted (distorted) and an appropriate decoder is needed for accurate speech recognition. Negotiating this standard is easier to find direction finding than, say, the GSM-digital cellular communication standard, whose mobile phones transmit and receive information in the form digital code... Stationary or stationary objects carrying out cellular communication are easiest to find, while mobile ones are more difficult, since the movement of a subscriber during a conversation is accompanied by a decrease in signal power and a transition to other frequencies (when transmitting a signal from one base station to a neighboring one).

Direction finding methods

The arrival of cellular communications in every family (today schoolchildren also receive such gifts) is a reality of the time, comfort is already becoming irreplaceable. The presence of a cell phone allows the user to identify his location, both at the current moment in time, and all his previous movements before. The current position can be identified in two ways.

The first is a method of targeted direction finding of a cell phone, which determines the direction to a working transmitter from three to six points and gives an intersection of the location of the radio signal source. The peculiarity of this method is that it can be applied at someone's order, for example, bodies authorized by law.

The second method is through a mobile operator, which automatically constantly registers where this or that subscriber is at a given time, even if he does not conduct any conversations. This registration takes place automatically according to the identifying service signals automatically transmitted by the cell phone to the base station (this was discussed earlier). The accuracy of determining the location of the subscriber depends on a number of factors: the topography of the area, the presence of interference and signal reflection from buildings, the position of the base stations and their congestion (the number of active mobile phones of the operator in a given cell), the size of the cell. Hence, the accuracy of determining the location of a cellular subscriber in a city is noticeably higher than in an open area, and can reach a spot of several hundred meters. Analysis of data on communication sessions of a subscriber with various base stations (from which and to which station the call was made, time of the call, etc.) allows you to restore a picture of all the movements of the subscriber in the past. The data is automatically registered with the mobile operator (for billing and not only ...), since the payment for such services is based on the duration of the use of the communication system. This data can be stored for several years, and this time is not yet regulated by federal law, only by departmental acts.
You can conclude - confidentiality is provided, but not for everyone. If it is necessary to eavesdrop on your conversations, or determine your location, almost any "equipped" special service, or criminal community, can do this without any effort.

It is more difficult to intercept a conversation if it is being conducted from a moving vehicle. the distance between the user of the cell phone and the direction finding equipment (if in question about analog communication) is constantly changing and if these objects move away from each other, especially in rough terrain among houses, the signal weakens. When moving quickly, the signal is transferred from one base station to another, with a simultaneous change operating frequency- this makes it difficult to intercept the entire conversation as a whole (if it is not conducted purposefully with the participation of the telecom operator), since to find new frequency it takes time.

You can draw conclusions from this yourself. Switch off your cell phone if you do not want your location to be known.

Telephone communication is a transmission speech information over long distances. With the help of telephony, people are able to communicate in real time.

If at the time of the emergence of technology there was only one method of data transmission - analog, then in currently the most different systems communications. Telephone, satellite and mobile connection, as well as IP telephony provide reliable contact between callers, even if they are at different ends the globe... How does telephony work with each method?

Good old wired (analog) telephony

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

The connection of two subscribers is regulated by dialing a number, 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 made the process cheaper, but the principle of operation of analog communication networks remained the same.

Mobile (cellular) communication

Subscribers of mobile operators mistakenly believe that they have "cut the wire" connecting them to telephone exchanges... It looks like it is - 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 look at how mobile communication works, we find not so many differences from the work of analog networks. The signal actually "is in the air", but 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 stage of radio transmission of data only covers the signal path from the telephone 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 the pros and cons?

The technology provides greater mobility compared to analog data transmission, but carries the same risks of unwanted interference and the possibility of wiretapping.

Cell signal path

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

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

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

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

Satellite connection

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

An individual subscriber gets the opportunity to travel practically without restrictions, staying in touch even in the taiga or in the jungle. A legal subscriber can bind a whole mini-automatic telephone exchange to one repeater antenna (this is a familiar "dish"), however, one should take into account the volume of incoming and outgoing, as well as the size of files that need to be sent.

Cons of technology:

• 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 the satellite transponder, the time that will pass before the full functionality is restored will take 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 this 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 areas;
• redundancy of channels that can be used in the event of a ground communication breakdown;
• flexibility of the technical characteristics of the network, allowing it to be adapted to almost any requirement.

Cons of technology:

• 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 repeater, the time that will pass before the system 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.

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 ​​action is determined by the surface wave, in the evening they are well reflected from the ionosphere and the area of ​​action 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 void 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 closely related and somewhat overlapping term is radio navigation, however, in radio navigation, the object whose coordinates are being 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 emission (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 image elements is selected in accordance with the radio channel bandwidth and physiological criteria. To narrow the bandwidth 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 a 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:

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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:

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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:

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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.

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A 900 MHz signal can hit up to 35 kilometers, although the "range" of some Base Stations located along the routes can be 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:

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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:

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

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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:

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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:

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

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

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

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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:

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

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

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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!