Cell phone device operating principle. Phone diagram and service instructions

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 the Beeline company and tried to figure out how cellular communications work...

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 signals from mobile phones at a distance of up to 35 kilometers and communicates with the mobile phone via service or voice channels.

After you have dialed a friend's number, your phone contacts the Base Station (BS) closest to you via a service channel and asks you to allocate a voice channel. The Base Station sends a request to the controller (BSC), which forwards it to the switch (MSC). If your friend is a subscriber to the same cellular network, then the switch will check the Home Location Register (HLR), find out where the called subscriber is currently located (at home, in Turkey or Alaska), and transfer the call to the appropriate switch from where it was sent will be sent to the controller and then to the Base Station. The Base Station will contact your mobile phone and connect you to your friend. If your friend is on a different network or you are calling a landline, your switch will contact the corresponding switch on the other network. Difficult? Let's take a closer look. The Base Station is a pair of iron cabinets locked in a well-conditioned room. Considering that it was +40 outside in Moscow, I wanted to live in this room for a while. Typically, the Base Station is located either in the attic of a building or in a container on the roof:

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 antenna connects the Base Station to the controller:

Each sector can handle up to 72 calls simultaneously, depending on setup and configuration. A Base Station can consist of 6 sectors, so one Base Station can handle up to 432 calls, however, a station usually has fewer transmitters and sectors installed. 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 travels further and penetrates better inside buildings 1800 MHz - the signal travels over shorter distances, but allows you to install a larger number of transmitters in 1 sector 2100 MHz - 3G Network This is what the cabinet looks like with 3G equipment:

900 MHz transmitters are installed at Base Stations in fields and villages, and in the city, where Base Stations are stuck like hedgehog needles, communication is mainly carried out at a frequency of 1800 MHz, although any Base Station may have transmitters of all three ranges simultaneously.

A signal with a frequency of 900 MHz can reach up to 35 kilometers, although the “range” of some Base Stations located along highways can reach up to 70 kilometers, due to the reduction in 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 optimal radio coverage at ground level. Therefore, despite a range of 35 kilometers, a radio signal is simply not sent to the aircraft’s flight altitude. However, some airlines have already begun installing low-power base stations on their aircraft that provide coverage within the aircraft. Such a BS is connected 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, for example, turning off the voice on night flights. The phone can measure the signal strength from 32 Base Stations simultaneously. It sends information about the 6 best (in terms of signal strength) via the service channel, and the controller (BSC) decides which BS to transfer 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. They also told me about the so-called “problem of the upper floors.” If you live in a penthouse, then sometimes, when moving from one room to another, the conversation may be interrupted. This happens because in one room the phone can “see” one BS, and in the second - another, if it faces the other side of the house, and, at the same time, these 2 Base Stations are located at a great distance from each other and are not registered as “ neighboring" from the mobile operator. In this case, the call will not be transferred from one BS to another:

Communication in the metro is provided in the same way as on the street: Base Station - controller - switch, with the only difference being that small Base Stations are used there, and in the tunnel, 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, but, for example, during some holidays the BS may not be able to cope with the number of people wanting to call. This usually happens on New Year's Day, when everyone starts congratulating each other. SMS are transmitted via service channels. On March 8 and February 23, people prefer to congratulate each other via SMS, sending funny poems, and phones often cannot agree with the BS on the allocation of a voice channel. I was told an interesting case. In one area of Moscow, subscribers began to receive complaints that they could not get through to anyone. Technical specialists began to figure it out. 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 going on and students were constantly exchanging text messages. The phone divides long SMS into several short ones and sends each one separately. Technical service staff advise sending such congratulations via 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:

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 subscriber’s movement and signal transmission from one BS to another. The switch looks much more interesting:

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

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The switch controls traffic. Remember the old movies where people first dialed the “girl”, and then she connected them to another subscriber by switching wires? Modern switches do the same thing:

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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 their colleagues from the Big Three:

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

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

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24-hour monitoring of 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 rates, statistics and feedback from subscribers. Just like in airplanes, all cellular network equipment has sensors that send a signal to the central control system and output information to dispatchers’ computers. If some equipment fails, the light on the monitor will begin to “blink.” The CCS also tracks statistics for all switches and controllers. He analyzes it, comparing it with previous periods (hour, day, week, etc.). If the statistics of any of the nodes began to differ sharply from previous indicators, then the light on the monitor will again begin to “blink”. Feedback is received by customer service operators. If they cannot resolve the problem, the call is transferred to a technician. If he turns out to be powerless, then an “incident” is created in the company, which is resolved by the engineers involved in the operation of the relevant equipment. The switches are monitored 24/7 by 2 engineers:

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

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

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Articles and Lifehacks

In our article we will briefly examine the internal structure of a modern mobile phone, focusing on each of the significant blocks.

We are talking specifically about push-button “tubes”; we will talk about the structure of a smartphone another time.

Case and keyboard

Today, almost all push-button models are produced in a plastic case.

The only exceptions are some designer phones, for example, titanium gadgets, but they can be ignored due to their low prevalence.

The vast majority of phones today are produced in the form factor; various clamshells and sliders have almost disappeared from the market. In them, the back panel is removable and often replaceable.

Thus, the user gets access to a slot for a SIM card, memory cards and battery.

The keyboard is most often made of rubber; usually the keys are backlit, making it easier to use the device in the dark.

Display

The screens of most modern push-button models are made using .

Logic block

A mobile phone, like a smartphone, is a specialized minicomputer. However, the element base it uses is completely different, so you won’t find the Qalcomm or MediaTek processors familiar to touch gadgets in handsets.

Moreover, model specifications almost never indicate either the type of chipset or even the amount of RAM.

The only thing that makes sense to talk about is the built-in storage, intended mainly for photos and music.

In addition, many cell phones support microSD cards, usually up to 32 GB in capacity. However, no more is required.

Particular mention should be made of the non-volatile memory, which stores the device’s unique code – IMEI.

Radio module

In addition to voice communication using the GSM standard, push-button devices are capable of surfing the Internet using GPRS technology.

Its data exchange speed is extremely low even in comparison with 3G, not to mention LTE, and operator tariffs make such communication completely unusable.

To ensure stable communication, the phones have an internal whip antenna.

Sometimes you can find models that support 3G Internet. This somewhat expands the capabilities of the device.

Audio system

In its simplest form, it consists of a microtelephone and a microphone, allowing you to use the gadget for its intended purpose - for conversations.

An almost integral part of the internal structure of any mobile phone is a special 3.5 mm headphone jack.

Some models also have a speaker that can be used for both hands-free communication and music playback.

SIM card

The SIM card represents the subscriber authentication key. Unlike smartphones, most handsets still use the mini-SIM standard.

There can be either one or two slots. The latter is more common in models equipped with a 3G module, so that you can separately connect a card for the Internet.

Camera

Unlike smartphones, not every phone has a camera. And where it does exist, its resolution is very modest - 0.3 megapixel modules are still found, at best you can hope for 3 megapixels.

Nothing surprising - you can hardly hope to find a two-module camera with optical zoom in a device for 2 thousand rubles. Therefore, you should not count on receiving high-quality photos in this case.

Battery

The battery provides power to all elements of the mobile device. It is usually removable; to remove it, you just need to remove the back panel. Modern models use two types of batteries: lithium-ion and lithium-polymer.

The latter are considered somewhat more progressive, since they were created in response to the tendency of lithium-ion batteries to swell and even explode.

As a result, the problems with push-button devices in this regard are the same as with smartphones: sensitivity to cold and a limited number of charge cycles.

Some users are still captivated by myths and believe that the battery has the so-called. "memory effect". There is nothing like this in modern phones.

The voltage used in modern models is usually 3.6 V.

Interfaces

This element is designed to interact with other devices.

Three options are possible:

Complete absence of interfaces in the most primitive models.
Bluetooth wireless interface that allows you to exchange files, for example, with another phone, desktop computer or laptop.
A USB port that allows you to connect your phone to a PC using a cable.

In the latter case, drivers for phones of a specific model may be needed if the device does not “pick up” on the fly.

Wi-Fi, which is usual for smartphone users, is absent in this case.

Other items

Feature phones have several internal devices that are not typically found in smartphones. This could be a flashlight or a vibrator that allows you to receive calls without turning on the call signal.

In all other respects, these gadgets are practically no different from each other.

Finally

As you can see, in the decades since the advent of cellular communications, the design of telephones has not changed much.

And, despite the dominance of smartphones in the mobile market, this category of devices is still not going to die out.

It has occupied a niche that meets the needs of those who do not require anything from the device other than its main function - the ability to talk with the interlocutor.

And if earlier push-button models appeared that had a claim to compete with touch-sensitive ones, today everything superfluous has disappeared from their design, leaving only the necessary minimum.

This allowed us to reduce the price of the device to an absolute minimum.

Today I want to talk about how to correctly read mobile phone diagrams. I will try to tell you the most basic things that a master should know. So. Where to begin? The first thing you need to know. This is what the microcircuits are called and how they are designated on the diagrams.

1. Processor. The processor is usually signed on the CPU or RAP, RAPIDO circuit. They are most often square and most often the largest. If it is Nokia, then in most cases there is a “skirt” along the rim of the processor. In new Nokia models you can often find a processor mounted on a flash drive. They are called “sandwich”, this is the worst thing that can happen after the compound) what is the compound sometime later.
2. Flash drive. A flash drive on the diagrams is written as flash and somewhere I came across mem, memory. It is most often rectangular in shape. And remember, in Nokia phones the processor and flash drive can only be changed in pairs. And they only fit from an identical model. What I mean is that, for example, Nokia 6233 and 6300 phones have the same processor. But this is only in appearance! They won't work!

3. Power controller. It is signed on the diagrams with different “names”: it can be written retu, tahvo, betty, UEM - all this is a power controller. Most of them are small square chips.
4. Also, any mobile phone has a receiver and transmitter RF chip and GSM FEM. You need to be more careful when replacing transmitters. Some look identical but the last numbers in the markings are different. But they don't work on other phones. Others may be similar and fundamentally different numbers but will work. In the process of work, you can do it for yourself. Using your experience, build a model compatibility diagram.
These were the most basic ones in my opinion. If you have any questions about microcircuits and their designation. And in general any questions regarding mobile phone repair. Ask in the comments or write on Skype. The number can be found in my contacts

Using the example of the Nokia 6233 phone, I’ll add a picture with the location of these parts

I remembered! There are 2 more important details in phones. Not everything is true. Briefly speaking. This is a thermistor and fuse. The fuse is most often used for charging. But in some phones it can also be found on camera. It burns out very often. And then you have to install a jumper. And a thermistor. What is a thermistor? This is such an insidious nasty thing)) The thermistor is in the phone charging circuit and is responsible for overheating. Very often this thermistor bursts after an impact or rots after water. Then the phone, when connected to the charger, starts writing “invalid battery” or “charger not allowed” or something else. I don’t remember everything anymore. In this case, it is a thermistor. How can they be found on the diagram? Yes, very simple! The fuse is located immediately behind the connector and is called FUSE, and the thermistor is BTemp. We must also remember. that the thermistor cannot be replaced by anything. Only with a different thermistor. Jumpers are snot) in this case do not roll. That's all for today. I'm tired of writing))

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

Mobile phones these days come with a range of features, and more and more of them are becoming available every day. Depending on your mobile phone model, you can do the following:

Save important information
Take notes or make a to-do list
Record important meetings and turn on alarms for reminders
use a calculator for calculations
send or receive mail
search for information (news, statements, jokes and much more) on the Internet
play games
watch TV
send messages
use other devices such as MP3 players, PDAs and GPS navigation systems.

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 talk about new features of mobile phones.

Let's start with the fact that a mobile phone is essentially a radio - a more advanced type, 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. This radiotelephone system operated using one main antenna installed on a tower outside 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 due to the limited number of channels.

The genius of the mobile system lies in dividing the city into several elements (“cells”). This promotes 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 the honeycomb (hexagon-shaped) that can most optimally cover the area.

In order to better understand the operation of a mobile phone, it is necessary to compare CB radio (i.e. regular radio) and cordless telephone.

Full-duplex portable device versus half-duplex - radiotelephones, like simple radios, are half-duplex devices. This means that two people share the same frequency, so they can only take turns speaking. 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 speaking. Therefore, you can talk on mobile phones at the same time.

Channels - a radiotelephone uses only one channel, a 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 phone system, a mobile phone user uses about 800 frequencies to talk around town. A mobile phone divides a city into several hundreds. Each cell has a specific size and covers an area of 26 km2. Honeycombs look like hexagons enclosed in a lattice.

Because mobile phones and stations use low-power transmitters, non-adjacent cells may use the same frequencies. The two cells may use the same frequencies. The cellular network consists of powerful high-speed computers, base stations (multi-frequency VHF transceivers) distributed throughout the entire working area of the cellular network, mobile phones and other high-tech equipment. We'll talk about base stations further, but now let's 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 grid) uses 1/7 of the available channels, which have their own set of frequencies and therefore do not overlap each other:

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, for each mobile phone user there are 395 communication channels (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 mobile technology, 1G, is considered an analogue of the cellular network. Since digital information transmission (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 transmission of the base station and mobile phone signal within each cell does not allow you to move far from the cell. In this way, 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 usually runs on battery power, is not significantly high. Low-power transmitters mean small batteries, which makes mobile phones more compact.

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

Mobile phone codes

Electronic Sequence Number (ESN) is a unique 32-bit number programmed into the mobile phone by the manufacturer.
Mobile Identification Number (MIN) is 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 cell phone when you purchase the 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's what happens during this time:

When you first turn on the phone, it looks for an identification code on the main control channel. A channel is a special frequency that mobile phones and the base station use 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 records the phone's position 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 contacts your mobile phone to tell you which frequency to use and after the mobile phone communicates with the antenna, the phone gains access to the network.

The cell phone and base station maintain constant radio contact. A cell phone periodically switches from one base station to another, which emits a stronger signal. If a cell phone moves out of the field of a base station, it establishes a connection with another, nearby base station, even during a conversation. The two base stations "communicate" through the Switching Center, which transmits a signal to your cell phone to change frequency.

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

Most modern cell phones can operate in several standards, which allows you to use roaming services 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 the 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 annoying thing about all this is that you can pay a pretty penny for roaming calls. On most phones, when you first cross the border, the roaming service is displayed. Otherwise, you better check your mobile coverage map so that you don’t have to pay “inflated” tariffs later. Therefore, check the cost of this service immediately.

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

In 1983, the first analog mobile telephone 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 engaged in the same business in the market. One such company in the United States 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 the other.

A version of the AMPS standard called NAMPS (Narrowband Advanced Communications System) uses new digital technologies to allow the system to triple its capabilities. But even though it uses new digital technologies, this version remains just analogue. Analog standards AMPS and NAMPS operate only at 800 MHz and cannot yet offer a wide variety of functions, such as Internet connectivity and mail.

Digital mobile phones belong to the second generation (2G) of mobile technology. They use the same radio technology as analog phones, albeit in a slightly different way. Analogue systems do not fully utilize the signal between the phone and the mobile network - analogue signals cannot be jammed or manipulated as easily as digital signals can. This is one reason why many cable companies are switching to 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 analog AMPS portal. Frequency modulation uses 2 frequencies, one for logic one and the other 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, a modulation and coding scheme are required. 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 regular phone consists of several parts:

The chip (board) that is the brain for the phone
Antenna
Liquid crystal display (LCD)
Keyboard
Microphone
Speaker
Battery

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

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

The ROM chips and memory card chip allow you to store mobile phone operating system data and other user data, such as phone book data. Radio frequency controls power and charging and handles hundreds of FM waves. The high-frequency amplifier controls the signals that are received or reflected by the antenna. Screen size has increased significantly since mobile phones have become more functional. Many phones have notebooks, calculators and games. And now many more phones are connected to a PDA or Web browser.

Some phones store certain information, such as SID and MIN codes, in 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 make sound at all. As you can see, the speakers are the same size as a small coin, and the microphone is no larger 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 parts occupied an entire floor of the building, but now all this fits in the palm of a person.

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

FDMA (Frequency Division Multiple Access) TDMA (Time Division Multiple Access) CDMA (Code Division Multiple Access)

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

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

FDMA places each phone call on a separate frequency. TDMA allocates each call a certain time on its assigned frequency. CDMA assigns a unique code to each call and then transmits it to a free frequency.

The last word of each method, multiple, means that each hundredth can be used by several people.

FDMA

FDMA (Frequency Division Multiple Access) is a method of using radio frequencies where only one subscriber is in the same frequency band, different subscribers use different frequencies within a cell. Is an application of frequency division multiplexing (FDM) in radio communications. 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 transmitting analog signals. And although this method can undoubtedly transmit digital information, it is not used because 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 slot, 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 time slots.

A narrow frequency band is usually understood as “channels”. Voice data converted into digital information is compressed, causing it to take up less space. Therefore, TDMA operates 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 range.

GSM

TDMA is currently the dominant technology for mobile cellular networks and is used in the GSM (Global System for Mobile Communications) standard (Russian SPS-900) - a global digital standard for mobile cellular communications, with channel sharing based on the TDMA principle and a high degree of security thanks 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 an Intel Pentium III. GSM systems use an encoding method to secure phone calls from mobile phones. The GSM network in Europe and Asia operates at 900 MHz and 1800 MHz, and in the USA at 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 anywhere the standard is supported. In order to connect to a specific mobile operator in different countries, GSM users simply change the 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 are not the same as the international system. So if you live in the US but really need a mobile phone abroad, you can buy a three or four band GSM phone and use it in your home country and abroad, or just buy a 900MHz/1800MHz GSM mobile phone for traveling abroad .

CDMA

CDMA (Code Division Multiple Access). Traffic channels with this method of dividing the medium are created by assigning each user a separate numeric code, which is distributed across 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, subscribers' broadcasts overlap each other, but since their codes are different, they can be differentiated. CDMA is the basis for IS-95 and operates on the 800 MHz and 1900 MHz frequency bands.

Dual band and dual standard mobile phone

When you go traveling, you undoubtedly want to find a phone that will work on 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 dual band TDMA phone can use TDMA services on an 800 MHz or 1900 MHz system. A dual band GSM phone can use GSM service in three bands - 850 MHz, 900 MHz, 1800 MHz or 1900 MHz.
Multi-standard 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 that do not support a digital network.
A multi-band/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 a phone supports two bands, then it connects to the 800 MHz network if it cannot connect to the 1900 MHz band. When a phone has multiple standards, it first uses the digital standard, and if this is not available, it switches to the analogue one.

Mobile phones come in two- and three-band modes. However, the word "three-lane" can be deceiving. It may mean that the phone supports 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 traveling abroad, it is better to purchase a phone that operates on the 900 MHz GSM band for Europe and Asia and 1900 MHz for the US, and also supports the analog standard. In essence, this is a dual-band phone in which one of these modes (GSM) supports 2 bands.

Cellular and Personal Communications Service

Personal Communications Service (PCS) is essentially a mobile phone service that emphasizes personal communications and mobility. The main feature of PCS is that the user's telephone number becomes his personal communication number (PCN), which is “tied” to the user himself, and not to his phone or radio modem. A global traveler using PCS can freely receive phone calls and emails on their PCN.

Cellular communications were originally created for use in cars, while personal communications meant greater possibilities. Compared to traditional cellular communications, PCS has several advantages. Firstly, it is completely digital, which provides higher data transfer rates and facilitates the use of data compression technologies. Secondly, the frequency range used for PCS (1850-2200 MHz) allows reducing the cost of communication infrastructure. (Since the overall dimensions of PCS base station antennas are smaller than the overall dimensions of cellular network base station antennas, their production and installation are cheaper).

In theory, the mobile system in the US 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, the PCS has 8 time slots and the channel spacing is 200 KHz, as opposed to the usual three time slots and 30 KHz between channels.

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, which are commonly called smartphones. Such phones have multiple bands and high-speed data transfer.

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

CDMA2000 is a further development of the 2nd generation CDMA One standard.
WCDMA (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 (English Time Division - Synchronous Code Division Multiple Access) is a Chinese standard for third generation mobile networks.

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

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

Cell 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 of the base stations, you can see that each mobile operator has installed its own equipment, which nowadays takes up very little space (at the base of older towers small rooms were built 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 by 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, a plate with green wires attached to it is a copper ground plane.

A mobile phone, like any other electronic device, may experience problems:

Most often, these include corrosion of parts caused by moisture entering the device. If moisture gets into your phone, you need to make sure that the phone is completely dry before turning it on.
Excessive temperatures (for example, in a car) can damage the battery or electronic circuit 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 you call anyone, your phone transmits 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 (using a special device) and intercept them. If these codes are used in another mobile phone, then you can make calls from it completely free of charge, since the owner of these codes will pay the bill.

The mobile phone is an integral part of a modern, technologically advanced society. Despite the commonality and apparent simplicity of this device, very few people know how a mobile phone works.

Mobile phone device

Modern technologies and constantly moving forward progress allow us to create phones with a huge number of functions and capabilities. With each new model, phones become thinner, more beautiful and more affordable. Despite the huge variety of models and manufacturers, all these devices are designed according to the same principle.

Essentially, a mobile phone is a receiving and transmitting device that has a receiver, transmitter and radio antenna in its body. The receiver receives a radio signal, converts it into electrical impulses and sends it to the speaker of your phone in the form of electrical waves. The speaker converts these electrical impulses into the sound that we hear when talking to the other person.

The microphone picks up your speech, converts it into electrical signals and sends it to the built-in transmitter. The transmitter's task is to convert electrical impulses into radio waves and transmit them to the nearest station via an antenna. The antenna serves to enhance the reception and transmission of radio waves from the phone to the nearest cellular station.

How does a landline phone work?

The design of a landline phone is not much different from a mobile phone. In a landline telephone there is no need to convert electrical impulses into radio waves, since contact with the subscriber occurs via a telephone cable through an Automatic Telephone Exchange (ATS). The station does not need to search for a device within its coverage area, and when you dial a number, it automatically connects you to the telephone set to which this number is registered.

How does mobile communication work?

Each of us has the opportunity to visually observe a large number of radio towers located in different parts of the city. These towers, as a rule, are installed on the highest possible places, on the roofs of high-rise buildings, on structures of other communications or on their own stationary towers. These radio towers are called base stations (BS). You may notice that in cities such stations are installed much more often than in intercity areas. This is due to the fact that in urban environments there is a lot of natural interference in the form of concrete buildings and various metal structures, which significantly degrade the signal quality. At the same time, a larger number of subscribers are concentrated in cities, which create a heavy load on the cellular network and in order to maintain good communication quality, increased coverage is required.

Your phone has its own identification in the form of your SIM card's mobile number. When turned on, the mobile phone constantly scans the area in search of a network and automatically selects the Base Station that provides the best signal quality. At the same time, it informs the station about its location and status, thus, the central computer of the cellular operator always knows which base station the phone is in coverage and whether it is ready to receive a call signal. As soon as another person calls your number, the computer detects your location and sends a ringing signal to your phone. If the phone is turned off or is not within range of the nearest Base Station, then the computer tells you that the subscriber is out of coverage and cannot receive a call.