People have long since learned to communicate at a distance. In ancient times, a messenger was sent with news, later letters were written. Now, to say a few words to a distant friend, you can just call him. The main thing is to have a cell phone with you. But how do they connect to each other if they don't even have wires? In this story, I will tell you how the phone works.

What it is?

A mobile phone is more like a walkie-talkie than a regular corded phone. Radio waves are used to transmit the signal.

The difference is that the walkie-talkies are connected to one antenna, and can only be connected by catching a signal from it. Cell phones are not tied to a specific station. While moving, they connect to the antenna from which the strongest signal is received, so we can use communication almost all over the world without changing the SIM card. Antennas, or base stations, have been built all over the world, hiding in billboards, clocks, poles, and even trees. Each of them is responsible for its own zone, which has the shape of a hexagon. In the diagrams, these territories bordering each other resemble a honeycomb. Hence the name - cellular communication.

Who was first?

Who do you think was the first to talk on a cell phone? Of course, it was an employee of Motorola, which released them. In 1973, while on the streets of New York, he called and boasted of a call from an unusual phone at that time to his main competitor. This phone became the prototype of the first mobile phone that hit the stores 10 years later.

For the phone to work, you need to insert a SIM card into it. It contains information about the subscriber, that is, about the person who uses it. The mobile phone starts checking all the frequencies available to it, there are about 160 of them. The six best signals are recorded on the SIM card, these are the signals of your network.

After you have dialed your buddy's number, your phone transmits information about you to the antenna with the strongest signal. Your operator (for example, MTS or Beeline) recognizes you, finds a free channel on which your conversation can take place, and connects you. All this takes only a few seconds.

The conversation itself is a rather complicated technical process. Our voice is broken into segments lasting 20 milliseconds and converted to digital format, then encoded by a special system. Encrypted signals are processed again to remove extraneous noise.

Now cellular telephone serves not only for conversations. One small device fits such simple mechanisms as a simple clock, alarm clock, calculator, calendar, flashlight, as well as complex cameras, Internet access, a player and much more.

Do you know what happens after you dial 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 distant Easter Island? Why does the conversation sometimes suddenly stop? Last week I visited Beeline and tried to figure out how 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, and 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 via service or voice channels.

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

Difficult? Let's take a closer look.

The Base Station is a pair of iron cabinets locked in a well-air-conditioned room. Given that in Moscow it was +40 on the street, I wanted to live in this room for a while. Usually, the Base Station is located either in the attic of the 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 phones, the round one connects the Base Station with the controller:

3.

Each sector can serve up to 72 calls at the same time, depending on the setup and configuration. A Base Station can consist of 6 sectors, so one Base Station can serve up to 432 calls, however, there are usually fewer transmitters and sectors installed in the station. Cellular operators prefer to install more BS to improve the quality of communication.

The Base Station can operate in three bands:

900 MHz - the signal at this frequency spreads further and better penetrates inside buildings
1800 MHz - the signal extends over shorter distances, but allows you to install more transmitters in 1 sector
2100 MHz - 3G network

This is what a cabinet with 3G equipment looks like:

4.

900 MHz transmitters are installed at Base Stations in fields and villages, and in the city, where Base Stations are stuck like needles in a hedgehog, communication is mainly 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 reach up to 35 kilometers, although the "range" of some Base Stations 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 up to 70 kilometers ...

All Base Stations are designed to provide optimum ground level radio coverage. Therefore, despite the range of 35 kilometers, the radio signal is simply not sent to the altitude of the aircraft. However, some airlines have already begun installing low-powered base stations on their aircraft that provide coverage inside the aircraft. Such a BS is connected to the 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 signal strength from 32 Base Stations simultaneously. It sends information about the 6 best (by signal level) 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 may make a mistake and transfer you to a BS with a worse signal, in which case the conversation may be interrupted. It may also turn out that at the Base Station that your phone has selected, all voice lines are busy. In this case, the conversation will also be interrupted.

I was also told about the so-called "top floor problem". If you live in a penthouse, then sometimes, when moving from one room to another, the conversation may 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 at a great distance from each other and are not registered as " neighboring" from a 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 at the same time. Usually this power is enough for the eyes, but, for example, during some holidays, the BS may not be able to cope with the number of people who want to call. This usually happens on New Year's Eve, when everyone starts to congratulate each other.

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

I was told an interesting story. From one district of Moscow, complaints began to come from subscribers that they could not get through anywhere. Technicians began to understand. Most of the voice channels were free, and all service channels were busy. It turned out that next to this BS there was an institute where exams were taking place and students were constantly exchanging text messages.

The phone divides long SMS into several short ones and sends each one separately. Employees of the technical service are advised to send such congratulations 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 controls 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. It already occupies a large hall filled with various cabinets with equipment:

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The switch performs traffic control. Remember the old movies where people first called the "girl", and then she connected them with another subscriber, rewiring the wires? Modern switches do 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 level of their own network, as well as the level of the network 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 captures information:

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

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There are 3 main areas for monitoring the cellular network: accident rate, statistics and feedback from subscribers.

Just like in airplanes, all cellular network equipment has sensors that send a signal to the MCC and output information to the dispatchers' computers. If any equipment is out of order, then the light on the monitor will begin to "blink".

The MSC 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 some of the nodes began to differ sharply from the previous indicators, then the light on the monitor will begin to "blink" again.

Feedback is received by subscriber service operators. If they cannot solve the problem, then the call is transferred to a technical specialist. If he also turns out to be powerless, then an "incident" is created in the company, which is solved by engineers involved in the operation of the corresponding equipment.

The switches are monitored around the clock by 2 engineers:

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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 lot 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 stay on topic. 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 out in front of me, and I did not have time to photograph it. Stay Tuned!

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

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

Good old wired (analogue) telephony

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

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

Mobile (cellular) communication

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

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

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

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

Cell signal path

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

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

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

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

Satellite connection

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

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

Technology cons:

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

Satellite communications: pros and cons

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

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

Technology cons:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Millions of people around the world use mobile phones because mobile phones have made it much easier to communicate with people all over the world.

Mobile phones present a range of features these days, and more and more every day. Depending on the mobile phone model, you can do the following:

Save important information
Take notes or make a to-do list
Record important appointments and turn on an alarm for a reminder
use a calculator for calculations
send or receive mail
search for information (news, sayings, anecdotes and more) on the Internet
play games
watch TV
send messages
use other devices such as MP3 player, PDA devices and GPS navigation system.

But haven't you ever wondered how a mobile phone works? And what makes it different from a simple landline phone? What do all these terms PCS, GSM, CDMA and TDMA mean? This article will focus on the new features of mobile phones.

Let's start with the fact that a mobile phone, in fact, is a radio - a more advanced form, but a radio nonetheless. The telephone itself was created by Alexander Graham Bell in 1876, and wireless communication a little later by Nikolai Tesla in the 1880s (the Italian Guglielmo Marconi first began talking about wireless communication in 1894). It was destined for these two great technologies to come together.

In ancient times, when there were no mobile phones, people installed radio phones in their cars to communicate. Such a radiotelephone system operated from a single main antenna mounted on a tower in the outskirts of the city and supported about 25 channels. To connect to the main antenna, the phone had to have a powerful transmitter - with a radius of about 70 km.

But not many could use such radio phones because of the limited number of channels.

The genius of the mobile system lies in the division of the city into several elements ("cells"). This encourages frequency reuse throughout the city, so millions of people can use mobile phones at the same time. "Honeycomb" was not chosen by chance, since it is with honeycombs (hexagonal shape) that the area can be most optimally covered.

In order to better understand how a mobile phone works, it is necessary to compare CB radio (i.e. conventional radio) and radiotelephone.

Full Duplex Portable Device vs. Half Duplex - A radiotelephone, like a simple radio, is a half duplex device. This means that two people use the same frequency, so they can only speak in turns. A mobile phone is a full duplex device, which means that a person uses two frequencies: one frequency is for hearing the person on the other side, the other is for talking. Therefore, you can talk on mobile phones at the same time.

Channels - The radiotelephone uses only one channel, the radio has about 40 channels. A simple mobile phone may have 1,664 channels or more.

In half-duplex devices, both radio transmitters use the same frequency, so only one person can talk. In full duplex devices, the 2 transmitters use different frequencies so people can talk at the same time. Mobile phones are full duplex devices.

In a typical US mobile system, a mobile phone user uses about 800 frequencies to talk around the city. A mobile phone divides the city into several hundred. Each cell has a certain size and covers an area of ​​26 km2. Honeycombs are like hexagons enclosed in a lattice.

Since mobile phones and stations use low power transmitters, non-adjacent cells can use the same frequencies. Two cells may use the same frequencies. The cellular network is powerful high-speed computers, base stations (multi-frequency VHF transceivers) distributed throughout the working area of ​​the cellular network, mobile phones and other high-tech equipment. We'll cover base stations later, but for now let's take a look at the "cells" that make up a cellular system.

One cell in an analog cellular system uses 1/7 of the available two-way communication channels. This means that each cell (out of 7 cells in the array) uses 1/7 of the available channels, which have their own set of frequencies and therefore do not overlap:

A mobile phone user usually receives 832 radio frequencies for talking around the city.
Each mobile phone uses 2 frequencies per call - the so-called. two-way channel - therefore, there are 395 communication channels for each mobile phone user (the remaining 42 frequencies are used by the main channel - we will talk about it later).

Thus, each cell has up to 56 available communication channels. This means that 56 people will be able to talk on mobile phones at the same time. The first 1G mobile technology is considered to be an analogue of the cellular network. Since digital transmission of information (2G) began to be used, the number of channels has increased significantly.

Mobile phones have built-in low-power transmitters, so they operate at 2 signal levels: 0.6 watts and 3 watts (for comparison, here is a simple radio that operates at 4 watts). Base stations also use low power transmitters, but they have their own advantages:

The signal transmission of the base station and mobile phone within each cell does not allow you to move far from the cell. Thus, both cells can reuse the same 56 frequencies. The same frequencies can be used throughout the city.
The charge consumption of a mobile phone, which is usually powered by a battery, is not significantly high. Low power transmitters mean a small battery, which makes mobile phones more compact.

The cellular network needs a number of base stations, regardless of the size of the city. A small town should have several hundred towers. All mobile phone users in any city are managed by one main office, which is called the Mobile Switching Center. This center controls all telephone calls and base stations in the area.

Mobile phone codes

The Electronic Device Sequence Number (ESN) is a unique 32-bit number programmed into the mobile phone by the manufacturer.
Mobile Identification Number (MIN) - A 10-digit code derived from a mobile phone number.
The System Identification Code (SID) is a unique 5-digit code assigned to each FCC company. The last two codes, MIN and SID, are programmed into the mobile phone when you buy a card and turn on the phone.

Each mobile phone has its own code. Codes are needed to recognize phones, mobile phone owners and mobile operators. For example, you have a mobile phone, you turn it on and try to make a call. Here is what is happening at this time:

When you first turn on the phone, it looks for an identification code on the main control channel. A channel is a specific frequency used by mobile phones and a base station to transmit signals. If the phone cannot find the control channel, then it is out of reach and the message "no network" is displayed on the screen.
When the phone receives an identification code, it checks it against its own code. If there is a match, the mobile phone is allowed to connect to the network.
Along with the code, the phone requests access to the network and the Mobile Switching Center fixes the position of the phone in the database, so the Switching Center knows which phone you are using when it wants to send you a service message.
The switching center receives calls and can calculate your number. At any time, he can look up your phone number in his database.
The switching center communicates with your mobile phone to tell you which frequency to use and after the mobile phone contacts the antenna, the phone gets access to the network.

The cell phone and the base station maintain constant radio contact. A cell phone periodically switches from one base station to another, from which a stronger signal comes. If a cell phone leaves the field of the base station while moving, then it establishes a connection with another, the nearest base station, even during a conversation. The two base stations "communicate" through the Switching Center, which sends a signal to your mobile phone to change frequency.

There are cases when, when moving, the signal passes from one cell to another belonging to another mobile operator. In this case, the signal does not disappear, but is transmitted to another mobile operator.

Most modern cell phones can work in several standards, which allows you to use roaming services (English roaming - vagrancy) in different cellular networks. The switching center whose cells you are now using connects to your switching center and asks for code confirmation. Your system transfers all data about your phone to another system and the Switching Center connects you to the cells of the new mobile operator. And the most amazing thing is that all this is done within a few seconds.

The most unpleasant thing about all this is that you can pay a tidy sum for roaming calls. On most phones, when you first cross the border, the roaming service is displayed. Otherwise, you'd better check your mobile coverage map so you don't have to pay "inflated" rates later. Therefore, check immediately the cost of this service.

Please note that the phone must work in multiple bands if you want to use the roaming service, because different countries use different bands.

In 1983, the first analogue mobile communication standard, AMPS (Advanced Mobile Telephone Service), was developed. This analog mobile communication standard operates in the frequency range from 825 to 890 MHz. In order to maintain competition and keep prices in the market, the US federal government required that there be at least two companies in the market engaged in the same activity. One such company in the US was the Local Telephone Company (LEC).

Each company had its own 832 frequencies: 790 for calls and 42 for data. To create one channel, two frequencies were used at once. The frequency range for the analog channel was typically 30 kHz. The transmission and reception range of the voice channel is separated by 45 MHz so that one channel does not overlap with the other.

A version of the AMPS standard called NAMPS (Narrow Band Enhanced Communications System) uses new digital technologies to make the system triple its capability. But even though it uses new digital technologies, this version remains just an analog. The analog standards AMPS and NAMPS only operate on 800 MHz and cannot yet offer a wide variety of features such as Internet connectivity and email.

Digital mobile phones belong to the second generation (2G) of mobile technologies. They use the same radio technology as analog phones, but in a slightly different way. Analog systems do not fully utilize the signal between the phone and the mobile network - analog signals cannot be jammed or manipulated as easily as digital signals can. This is one of the reasons why many cable companies are moving digital so they can use more channels in a given band. It's amazing how effective a digital system can be.

Many digital mobile systems use frequency modulation (FSK) to transmit and receive data through the AMPS analog portal. Frequency modulation uses 2 frequencies, one for logic one, one for logic zero, choosing between the two, when transmitting digital information between the tower and the mobile phone. In order to convert analog information into digital and vice versa, modulation and a coding scheme are needed. This suggests that digital mobile phones must be able to process data quickly.

In terms of "complexity per cubic inch," mobile phones are among the most complex modern devices. Digital mobile phones can perform millions of calculations per second in order to encode or decode a voice stream.

Any ordinary phone consists of several parts:

Chip (board), which is the brain for the phone
Antenna
Liquid Crystal Display (LCD)
Keyboard
Microphone
speaker
Battery

The microcircuit is the center of the whole system. Next, we will look at what kind of chips there are and how each of them works. The analog-to-digital conversion chip encodes the outgoing audio signal from the analog system to digital and the incoming signal from the digital system to analog.

A microprocessor is a central processing unit responsible for performing the bulk of the information processing work. It controls the keyboard and display, and many other processes.

The ROM chips and the memory card chip can store mobile phone operating system data and other user data such as phone book data. Radio frequency controls power and charge, and works with hundreds of FM waves. The high-frequency amplifier controls the signals that arrive at or are reflected by the antenna. The screen size has increased significantly since the mobile phone has more features. Many phones have notebooks, calculators, and games. And now many more phones connect to a PDA or a Web browser.

Some phones store certain information, such as SID and MIN codes, in the built-in flash memory, while others use external cards such as SmartMedia cards.

Many phones have speakers and microphones so tiny that it's hard to imagine how they even make sound. As you can see, the speakers are the same size as a small coin, and the microphone is no bigger than a watch battery. By the way, such watch batteries are used in the internal chip of a mobile phone to operate the watch.

The most amazing thing is that 30 years ago, many of these details occupied the entire floor of the building, and now it all fits in the palm of a person.

There are three most common ways in which 2G mobile phones use radio frequencies to transmit information:

FDMA (Frequency Division Multiple Access - frequency division multiple access) TDMA (Time Division Multiple Access - time division multiple access) CDMA (Code Division Multiple Access) - code division multiple access.

Although the names of these methods seem so confusing, you can easily guess how they work by simply breaking the name into separate words.

The first word, frequency, time, code, indicates the access method. The second word, division, means that it separates calls based on the access method.

FDMA places each phone call on a separate frequency TDMA allocates a specific time for each call on the specified frequency CDMA assigns a unique code to each call and then transmits it to a free frequency.

The last word of each multiple method - “multiple” indicates that several people can use each hundredth.

FDMA

FDMA (Frequency Division Multiple Access) is a method of using radio frequencies when there is only one subscriber in one frequency band, different subscribers use different frequencies within a cell. It is an application of frequency multiplexing (FDM) in radio communications. In order to better understand how FDMA works, we need to look at how radios work. Each radio station sends its signal to free frequency bands. The FDMA method is used primarily for the transmission of analog signals. And although this method can undoubtedly transmit digital information, it is not used, since it is considered less effective.

TDMA

TDMA (Time Division Multiple Access) is a method of using radio frequencies, when there are several subscribers in the same frequency interval, different subscribers use different time slots (intervals) for transmission. It is an application of Time Division Multiplexing (TDM) to radio communications. When using TDMA, a narrow frequency band (30 kHz wide and 6.7 milliseconds long) is divided into three timeslots.

A narrow frequency band is usually understood as "channels". The voice data converted into digital information is compressed, due to which it takes up less space. Therefore, TDMA is three times faster than an analog system using the same number of channels. TDMA systems operate on the 800 MHz (IS-54) or 1900 MHz (IS-136) frequency band.

GSM

TDMA is currently the dominant technology for mobile cellular networks and is used in the GSM (Global System for Mobile Communications) (Russian SPS-900) standard - a global digital standard for mobile cellular communications, with channel separation based on the TDMA principle and a high degree of security due to public key encryption. However, GSM uses TDMA and IS-136 access differently. Let's imagine that GSM and IS-136 are different operating systems that run on the same processor, for example, both Windows and Linux operating systems run on Intel Pentium III. GSM systems use a coding method to secure phone calls from mobile phones. The GSM network in Europe and Asia operates at a frequency of 900 MHz and 1800 MHz, and in the USA at a frequency of 850 MHz and 1900 MHz and is used in mobile communications.

Blocking your GSM phone

GSM is the international standard in Europe, Australia, most of Asia and Africa. Mobile phone users can buy one phone that will work wherever this standard is supported. In order to connect to a specific mobile operator in different countries, GSM users simply change their SIM card. SIM cards store all the information and identification numbers that are needed to connect to a mobile operator.

Unfortunately, the 850MHz/1900MHz GSM frequencies used in the US do not match those of the international system. So if you live in the US but really need a mobile phone abroad, you can buy a 3- or 4-band GSM phone and use it at home and abroad, or just buy a 900MHz/1800MHz GSM mobile phone to travel abroad. .

CDMA

CDMA (Code Division Multiple Access). Traffic channels with this method of media separation are created by assigning each user a separate numeric code, which is distributed over the entire bandwidth. There is no time division, all subscribers constantly use the entire channel width. The frequency band of one channel is very wide, the broadcasts of subscribers overlap but, since their codes are different, they can be differentiated. CDMA is the basis for IS-95 and operates in the 800 MHz and 1900 MHz frequency bands.

Dual band and dual standard mobile phone

When you are going to travel, you certainly want to find a phone that will work in several bands, in several standards, or will combine both. Let's take a closer look at each of these possibilities:

A multiband phone can switch from one frequency to another. For example, a two-band TDMA phone may use TDMA services on either the 800 MHz or 1900 MHz system. A dual-band GSM phone can use the GSM service in three bands - 850 MHz, 900 MHz, 1800 MHz or 1900 MHz.
Multistandard phone. "Standard" in mobile phones means the type of signal transmission. Therefore, a phone with AMPS and TDMA standards can switch from one standard to another if necessary. For example, the AMPS standard allows you to use an analog network in areas where a digital network is not supported.
The multiband/multi-standard phone allows you to change the frequency band and transmission standard.

Phones that support this feature automatically change bands or standards. For example, if the phone supports dual bands, then it connects to the 800 MHz network, if it cannot connect to the 1900 MHz band. When a phone has more than one standard, it first uses the digital standard, and if there is none, it switches to analog.

Mobile phones are two- and three-band. However, the word "three-lane" can be misleading. It may mean that the phone supports the CDMA and TDMA standards, and the analog standard. And at the same time, it can mean that the phone supports one digital standard in two bands and an analog standard. For those who travel abroad, it is better to purchase a phone that operates on the GSM band 900 MHz for Europe and Asia and 1900 MHz for the US, and also supports the analog standard. In essence, it is a two-band phone with one of these modes (GSM) supporting 2 bands.

Cellular and personal communication service

Personal Communication Service (PCS) is essentially a mobile phone service that emphasizes personal communication and mobility. The main feature of PCS is that the user's phone number becomes his personal communication number (Personal Communication Number - PCN), which is "attached" to the user himself, and not to his phone or radio modem. A user traveling the world using PCS can freely receive phone calls and e-mails on his PCN.

Cellular communication was originally created for use in cars, while personal communication implied greater possibilities. Compared to traditional cellular service, PCS has a number of advantages. Firstly, it is completely digital, which provides a higher data transfer rate and facilitates the use of data compression technologies. Secondly, the frequency range used for PCS (1850-2200 MHz) reduces the cost of the communication infrastructure. (Since the overall dimensions of PCS base station antennas are smaller than the overall dimensions of cellular network base station antennas, they are cheaper to manufacture and install).

Theoretically, the US mobile system operates on two frequency bands - 824 and 894 MHz; PCS operates at 1850 and 1990 MHz. And since this service is based on the TDMA standard, PCS has 8 timeslots and 200KHz channel spacing, as opposed to the usual 3 timeslots and 30KHz channel spacing.

3G is the latest technology in mobile communications. 3G means that the phone belongs to the third generation - the first generation is analog mobile phones, the second is digital. 3G technology is used in multimedia mobile phones, commonly referred to as smartphones. These phones have multiple bands and high speed data.

3G uses several mobile standards. The most common are three of them:

CDMA2000 is a further development of the 2nd generation CDMA One standard.
WCDMA (English Wideband Code Division Multiple Access - broadband CDMA) is the radio interface technology chosen by most cellular operators to provide broadband radio access to support 3G services.
TD-SCDMA (Eng. Time Division - Synchronous Code Division Multiple Access) is a Chinese third-generation mobile network standard.

The 3G network can transfer data at speeds up to 3 Mbps (so it only takes about 15 seconds to download a 3 minute MP3 song). Let's take second-generation mobile phones for comparison - the fastest 2G phone can reach data transfer speeds up to 144 Kb / s (it takes about 8 hours to download a 3-minute song). High-speed 3G data transfer is just perfect for downloading information from the Internet, sending and receiving large multimedia files. 3G phones are a kind of mini laptops that can run large applications such as streaming video from the Internet, sending and receiving faxes, and downloading email messages with applications.

Of course, this requires base stations that transmit radio signals from phone to phone.

Mobile phone base stations are cast metal or lattice structures that rise hundreds of feet into the air. This picture shows a modern tower that "serves" 3 different mobile operators. If you look at the base station base, you can see that each mobile operator has installed its own equipment, which today takes up very little space (small rooms were built at the base of older towers for such equipment).

Base station. photo from http://www.prattfamily.demon.co.uk

A radio transmitter and receiver are placed inside such a block, thanks to which the tower communicates with mobile phones. The radios are connected to the antenna on the tower with several thick cables. If you look closely, you will notice that the tower itself, all the cables and equipment of the companies at the base of the base stations are well grounded. For example, the plate with green wires attached to it is a copper ground plate.

In a mobile phone, as in any other electronic device, problems may occur:

Most often, these include corrosion of parts caused by moisture entering the device. If moisture gets into the phone, make sure that the phone is completely dry before turning it on.
Too high a temperature (for example, in a car) can damage the battery or the electronic board of the phone. If the temperature is too low, the screen may turn off.
Analog mobile phones often face the problem of "cloning". A phone is considered "cloned" when someone intercepts its identification number and can call other numbers for free.

Here's how "cloning" works: Before calling anyone, your phone broadcasts its ESN and MIN codes to the network. These codes are unique and it is thanks to them that the company knows to whom to send the invoice for calls. When your phone transmits MIN/ESN codes, someone can hear (with a special device) and intercept them. If these codes are used in another mobile phone, then it will be possible to call from it completely free of charge, since the owner of these codes will pay the bill.