How does a mobile (cell) phone work? Block diagram of a GSM cell phone

General design of mobile phone RF circuits helpmymac wrote in April 9th, 2013

When repairing cell phones, you simply must know the structure of RF circuits. Understanding the structure of this part of the phone, you will not have questions when solving problems like “No signal”, “Weak signal”, etc. The RF part is responsible for the radio frequency component of the mobile phone, that is, for receiving and transmitting data.

Let's look at the block diagram and understand how it works.
In the normal situation (when no one is calling and no SMS is being sent at the moment), the phone works for reception. The so-called RX part is always active and ready to receive information, and the Antenna Switch is open in the RX direction.

During a call or sending SMS, Antenna Switch closes in the RX direction and switches to the TX side. All data is processed in the Baseband processor, that is, the received data goes straight to it. And before sending, the data is also initially processed in the Baseband processor.

Let's take a closer look at all the components:
RF Reciver (radio frequency receiver)
RF Reciver is called RX, this chip is responsible for receiving the signal. A malfunction of this chip will result in the phone being unable to receive any data.

RF Transmitter (radio frequency transmitter)
RF Transmitter is called TX, it is responsible for transmitting data from a mobile phone. Failure of this part will result in the inability to transfer data from the phone.

Power Amplifier RFPA (Radio Frequency Power Amplifier)
RFPA is an amplifier. The signal leaving the TX gets to the RFPA and only then gets to the antenna. In modern phones, two amplifiers are made for different ranges. When the phone is not calling anywhere, RFPA does not consume anything. When we decide to make a call, the power amplifier begins to consume 1A. Then the base station gives the command to reduce power. If the RFPA malfunctions, the signal will be lost or the signal indication will jump. A faulty RFPA can draw more than 2A of current.

Antenna. A poor signal may be due to a damaged antenna.

Antenna switch. Works as a channel that regulates where to send data. Either receiving data from RX or transmitting data from TX. If there is a malfunction, it may be in the closed position and as a result there will be no signal.

The RF part is usually hidden under a metal shield, unlike the Baseband Processor. This is due to the fact that it is susceptible to radio frequency interference and that is why it is protected from external influences.

Cellular communication is considered one of the most useful inventions of mankind - along with the wheel, electricity, the Internet and the computer. And in just a few decades, this technology has gone through a number of revolutions. Where did wireless communication begin, how do cells work, and what opportunities will the new mobile standard open up? 5G?

The first use of mobile telephone radio dates back to 1921 - then in the United States, the Detroit police used one-way dispatch communication in the 2 MHz band to transmit information from a central transmitter to receivers in police cars.

How did cellular communication come about?

The idea of cellular communications was first put forward in 1947 by Bell Labs engineers Douglas Ring and Ray Young. However, real prospects for its implementation began to emerge only in the early 1970s, when company employees developed a working architecture for the cellular hardware platform.

Thus, American engineers proposed placing transmitting stations not in the center, but in the corners of the “cells,” and a little later a technology was invented that allowed subscribers to move between these “cells” without interrupting communications. After this, it remains to develop operating equipment for such technology.

The problem was successfully solved by Motorola - its engineer Martin Cooper demonstrated the first working prototype of a mobile phone on April 3, 1973. He called the head of the research department of a competitor company straight from the street and told him about his own successes.

Motorola management immediately invested $100 million in the promising project, but the technology entered the commercial market only ten years later. This delay is due to the fact that it was first necessary to create a global infrastructure of cellular base stations.

In the United States, AT&T took up this work - the telecommunications giant obtained licensing of the necessary frequencies from the federal government and built the first cellular network that covered the largest American cities. The first mobile phone was the famous Motorola DynaTAC 8000.

The first cell phone went on sale on March 6, 1983. It weighed almost 800 grams, could work on a single charge for 30 minutes of talk time and could be charged for about 10 hours. Moreover, the device cost $3,995 - a fabulous sum at that time. Despite this, the mobile phone instantly became popular.

Why is the connection called cellular?

The principle of mobile communications is simple - the territory in which subscribers are connected is divided into separate cells or “cells”, each of which is served by a base station. At the same time, in each “cell” the subscriber receives identical services, so he himself does not feel the crossing of these virtual boundaries.

Typically, a base station in the form of a pair of iron cabinets with equipment and antennas is placed on a specially built tower, but in the city they are often placed on the roofs of high-rise buildings. On average, each station picks up signals from mobile phones at a distance of up to 35 kilometers.

To improve the quality of service, operators are also installing femtocells - low-power and miniature cellular stations designed to serve a small area. They can dramatically improve coverage in places where it is needed. Cellular communications in Russia will be combined with space

A mobile phone located on the network listens to the air and finds a signal from the base station. In addition to the processor and RAM, a modern SIM card contains a unique key that allows you to log in to the cellular network. Communication between the phone and the station can be carried out using different protocols - for example, digital DAMPS, CDMA, GSM, UMTS.

The cellular networks of different operators are connected to each other, as well as to the landline telephone network. If the phone leaves the range of the base station, the device establishes communication with others - the connection established by the subscriber is quietly transmitted to other “cells”, which ensures continuous communication while moving.

In Russia, three bands are certified for broadcasting - 800 MHz, 1800 MHz and 2600 MHz. The 1800 MHz band is considered the most popular in the world, as it combines high capacity, long range and high penetration. This is where most mobile networks now operate.

What mobile communication standards are there?

The first mobile phones worked with 1G technologies - this is the very first generation of cellular communications, which was based on analog telecommunications standards, the main one of which was NMT - Nordic Mobile Telephone. It was intended exclusively for transmitting voice traffic.

The birth of 2G dates back to 1991 - GSM (Global System for Mobile Communications) became the main standard of the new generation. This standard is still supported today. Communication in this standard has become digital, and it has become possible to encrypt voice traffic and send SMS.

The data transfer rate within GSM did not exceed 9.6 kbit/s, which made it impossible to transmit video or high-quality audio. The GPRS standard, known as 2.5G, was designed to solve the problem. For the first time, it allowed mobile phone owners to use the Internet.

This standard has already provided data transfer rates of up to 114 Kbps. However, it soon also ceased to satisfy the ever-increasing demands of users. To solve this problem, the 3G standard was developed in 2000, which provided access to Network services at a data transfer speed of 2 Mbits.

Another difference of 3G was the assignment of an IP address to each subscriber, which made it possible to turn mobile phones into small computers connected to the Internet. The first commercial 3G network was launched on October 1, 2001 in Japan. Subsequently, the throughput of the standard was repeatedly increased.

The most modern standard is fourth-generation 4G communications, which is intended only for high-speed data services. The throughput of the 4G network can reach 300 Mbit/s, which gives the user almost unlimited possibilities for surfing the Internet.

Cellular communications of the future

The 4G standard is designed for continuous transmission of gigabytes of information; it does not even have a channel for voice transmission. Due to extremely efficient multiplexing schemes, downloading a high-definition movie on such a network will take the user 10-15 minutes. However, even its capabilities are already considered limited.

In 2020, the official launch of the new generation of 5G communications is expected, which will allow the transfer of large amounts of data at ultra-high speeds of up to 10 Gbit/s. In addition, the standard will allow up to 100 billion devices to be connected to high-speed Internet.

It is 5G that will allow the true Internet of Things to emerge - billions of devices will exchange information in real time. According to experts, network traffic will soon increase by 400%. For example, cars will begin to constantly be on the global Internet and receive data about the road situation.

Low latency will enable real-time communication between vehicles and infrastructure. Reliable, always-on connectivity is expected to open the door to fully autonomous vehicles on the road for the first time.

Russian operators are already experimenting with new specifications - for example, Rostelecom is working in this direction. The company signed an agreement on the construction of 5G networks in the Skolkovo innovation center. The implementation of the project is part of the state program “Digital Economy”, recently approved by the government.

Mobile phone device.

Processor and memory

A mobile phone, like any computer, operates according to a program recorded in memory chips. Different mobile phone manufacturers use either their own or third-party processors. If the microprocessor is proprietary, then most likely it includes functional units that are not traditionally identified with a microprocessor. This could be audio processing, call control, etc.
Some phones contain (for example, SonyEricsson) contain 2 processors - the main Main CPU (AVR chip) and the Modem CPU (ARM chip). The Main CPU powers most of the phone's functions, including language packs. Modem CPU serves for infrared communication (IRDA), Bluetooth and for data and fax transmission.
A very important element in a microprocessor system is memory. Let us consider this issue in more detail, since many people are confused in the classification of memory chips.

Memory chips according to their purpose can be divided into the following two large groups.

1. ROM(Read Only Memory) - memory intended in a specific microprocessor system for read only (the Russian name is ROM - read-only memory, although this name is not entirely correct). Used to store programs.

These microcircuits are in turn divided into:
- volatile and non-volatile - according to the degree of dependence on power supply;
- once programmable (PROM - Programmable ROM) and repeatedly programmable (EPROM - Erasable Programmable ROM or Electrically Programmable ROM - erasable programmable ROM or electrically programmable ROM) - by the number of write cycles;
- with ultraviolet, x-ray or electrical (EEPROM - Electronically Erasable PROM and Flash) erasing, using the erase before writing method.

2. RAM(Random Access Memory) - random access memory, used as operational memory in a specific microprocessor system. Divided into:
- static (SRAM) and dynamic (DRAM), depending on the method of storing information. Dynamic uses electrical capacity to store information, the energy of which must be periodically replenished - hence the name;
- volatile and non-volatile - according to the degree of dependence on the power supply.

Mobile phones use Flash, EEPROM (no longer used lately) and DRAM. The main distinguishing feature of EEPROM and Flash is the possibility of reprogramming when connected to a standard system bus of a microprocessor device. Let's take a closer look at EEPROM and Flash.

EEPROM- allows you to erase a single cell using electric current. This is a relatively long process. However, each cell is erased automatically when new information is written to it, i.e. you can change the data in any cell without affecting the others. EEPROM - non-volatile memory. The disadvantage is the high cost.

Flash memory- a special type of non-volatile rewritable semiconductor memory.
It is analogous to a hard drive, because reading and writing are carried out sequentially bit by bit.

Translations of the word flash: short frame (film), flash, flash, blinking, flickering, annealing (glass). Flash memory gets its name from the way this type of memory is erased and written. The name was given by Toshiba during the development of the first flash memory chips (in the early 1980s) as a characteristic of the speed of erasing the flash memory chip in a flash - in the blink of an eye.
Flash memory is historically derived from ROM memory and functions similarly to RAM. Flash stores data in memory cells similar to cells in DRAM. Unlike DRAM, data in flash memory is not lost when the power is turned off.
Replacement of SRAM and DRAM memory with flash memory does not occur due to two features: flash is significantly slower and has a limit on the number of rewrite cycles (from 10,000 to 1,000,000 for different types).
The main advantage of flash memory over hard drives and CD-ROM media is that flash memory consumes significantly (about 10-20 times or more) less energy during operation. In CD-ROM devices, hard drives, cassette tapes and other mechanical storage media, most of the energy is spent driving the mechanics of these devices. In addition, flash memory is more compact than most other mechanical media.
So, due to low power consumption, compactness, durability and relatively high speed, flash memory is ideal for use as storage in mobile phones.
The main difference between flash memory and EEPROM is that erasing the contents of cells is performed either for the entire chip or for a specific block (cluster, frame or page). You can erase both the block and the contents of the entire microcircuit at once. Thus, in order to change one byte, first the entire block containing the byte to be changed is read into the buffer, the contents of the block are erased, the value of the byte in the buffer is changed, and then the block changed in the buffer is written. This scheme significantly reduces the speed of writing small amounts of data into random memory areas, but significantly increases the performance when writing data sequentially in large portions. Information recorded on flash memory can be stored for a long time (from 20 to 100 years) and can withstand significant mechanical loads (5-10 times the maximum permissible for conventional hard drives).

Memory device.

Mobile phone processors work with two types of memory.
1. ROM(Read Only Memory) - memory intended only for reading during phone operation with the ability to write to it during reprogramming. A small area of ROM dedicated to boot programs (analogous to a PC's BIOS) is located in the processor. The main ROM area uses a Flash memory chip. The main exchange during reprogramming is carried out with this microcircuit. This memory is non-volatile - when the power is turned off, the information is retained. Additional areas on removable flash cards are also used.
2. RAM(Random Access Memory) - random access memory used as operational memory, i.e. for temporary storage of data. This memory is volatile - when the power is turned off, the information disappears. The operating system is loaded into it and then runs. Sometimes it is built into the processor. Many phones use a separate chip for it.

The entire amount of memory that the phone's processor can work with is filled with data that has its own purpose and specific location. Consider the phone's memory distribution map

As already mentioned, the entire memory area consists of two parts - ROM and RAM. Let's look at them in order.

The processors of all phones include a small ROM area in which the following are located:
- boot program that starts working when you turn on the phone;
- a program that controls the initial process of data exchange with a computer.

The rest, a much larger part of the ROM, is located in the Flash memory chip, as well as on removable cards. Flash memory, in turn, is divided into the following main areas:
- BOOT CORE – operating system loader.
- EEPROM - this area contains phone settings (factory phone number (IMEI), network blocking codes, user, radio calibration, games, display settings and much more...) and appeared because new phones no longer have a separate EEPROM chip .
- LANG, PPM – data block in which the language package is stored. Since there are a large number of languages and fonts around the world, one PPM block can store from 1 to 20 languages. Changing the language pack is the main reason for changing PPM. The PPM block is rewritten with the same version in case of data corruption.
- MCU – the main program (operating system) with all the functions necessary for the phone to operate. MCU from one model cannot be used for another. MCU replacement is done to eliminate factory defects or add new functions, as well as in case of data corruption in flash memory (software repair).
- OTP – a one-time programmable memory area that contains the phone’s “fingerprints” - information that is unique to this phone without the right to change it.
- CONTENT - pictures, melodies, JAVA applications, calls, SMS messages, address book, etc. A removable card (MMC or FLEX) can be used for this area.
- FS – file system in which CONTENT is located.

ROM (Flash memory) is similar to a hard drive that stores operating system data. However, the operating system itself runs from RAM (random access memory), where it is loaded after the phone is powered on. RAM is either contained on a separate chip or built into the processor.

There are several ways to connect a mobile phone to a computer:

I. Phone-computer connection (A)

This connection is made using a Data cable, which connects the information output of the phone to the computer port.

Connecting to a computer opens up the following options:

2. It is possible to add, delete, change the phone book on the computer.

3. It is possible to record various content (ringtones, pictures, etc.) into the phone.

4. It is possible to send and receive SMS messages (short text messages) from the computer keyboard, using the phone as a wireless modem (GSM modem) - you need to take into account that you also have to pay for such SMS.

Cables come in 4 types, COM, USB->COM, LPT, USB:

COM provide coordination of the electrical interface of the mobile phone with the RS 232 interface.

RS-232 is an interface for transmitting information between two devices at a distance of up to 20 m. Information is transmitted over wires with signal levels different from standard 5V to ensure greater resistance to interference. Asynchronous data transfer is carried out at a set speed when synchronized by the level of the start pulse signal.

RS-232 uses two signal levels: logical 1 and 0. Logical 1 is sometimes denoted MARK, logical 0 - SPACE. Logical 1 corresponds to negative voltage levels (-3..-10), and logical 0 corresponds to positive voltage levels (+3..+10).

Circuit diagram of the MAX-232 interface converter chip.

This circuit uses a two-wire bidirectional serial interface (universal, FBus) - uses two wires to transmit information in two directions (Tx - Transmit, Rx - Receive) and GND - ground (see figure below). It is most convenient to take + 5V power directly from the computer (for example, from a USB connector). The ignition/autoignition signals are supplied to the phone charging voltage input. LEDs serve to indicate exchange.

Single wire bidirectional serial interface(MBUS, CBUS) - uses one wire to transmit information in two directions and GND - ground. Used in Nokia and Bosch phones to work with EEPROM and to synchronize with a computer. It is obtained if in the previous diagram Rx and Tx are connected according to the diagram in the figure.

The operation of USB -> COM cables looks a little more complicated; first, a virtual COM port is created on the computer, and then the electrical interface of the phone is coordinated with this port. To solve this problem, the PL 2303 microcircuit was developed.

2.1 Installing the driver for the USB data cable

The driver must be installed with the USB cable disconnected, that is, the data cable should not be connected to the computer.

Install the driver for the USB cable.

Open the folder with the driver, you will see two folders: the INF folder and the SETUP folder. Open the SETUP folder and see the PL-2303 Driver Installer file and run it. The program prompts you to begin installing the driver. Click the Next button and the driver installation begins. After clicking the Finish button, the driver installation is completed.

We reboot the computer. Connect the cable to the USB port. New devices are automatically found and recognized. The system informs you about this in the lower right corner of the taskbar.

To configure the program to work with your phone, you will definitely need information about which COM port the data cable drivers emulate.

Right-click on the "My Computer" folder and select the "Properties" section -> the "Hardware" tab -> the "Device Manager" section -> the "Ports (COM & LPT)" section

Find Prolific USB-to-Serial Comm Port (COM*), where * is the virtual COM port that will be used when working with the cable.

Click on Prolific and right-click on "Properties" - tab "Port Parameters" - set the speed to 115200.

We connect the phone to the data cable.

We launch the program for working with the phone and set the COM port used by the driver, as well as the speed of the port (depending on the model of the device, in most cases 115200 or 57600 bps).

Parallel interfaceLTP used to increase the exchange speed for reprogramming Nokia phones, some SonyEricsson, Sagem models. For older Nokia types, this interface is called Nokia flasher, where in addition to Rx, Tx and Gnd, MBUS and BTEMP signals are used. The 74HC14 chip is used (analogous to 1564TL2 - six Schmidt triggers). It is most convenient to take + 5V power directly from the computer (for example, from a USB connector).

USB– interface. The main feature of the standard is the ability for users to work in Plug&Play mode with peripheral devices. This means the ability to connect the device to a running computer, automatically recognize it immediately after connection and then install the appropriate drivers. Power for low-power devices is supplied from the bus itself. The bus speed is sufficient for the vast majority of peripheral devices. The USB interface works with new Motorola models on the P2K platform. On its basis, specialized programmers have been created, including those that emulate the operation of a regular COM port. The pinout of the connector socket installed in the computer is shown in the figure, and the assignment of the contacts is in the table.

Table. USB connector pin assignments.

Most programs work through a universal interface. It is enough to assemble the above circuit, find the corresponding phone connector, correctly switch the Rx, Tx, Gnd and +5V signals and connect the interface to the phone. The pinout (pinout) of connectors for many phones can be found at http://pinouts.ru

Features of programming using the channelA

This section begins an introduction to mobile phone programming techniques. Let's start with phones manufactured by Siemens x35, x45 series and Nokia DCT-3 platform. Here and below, the letter “x” denotes the series of this model range: “c”, “s”, “m”, “me”, “sl”. You will be able to change software versions in your mobile phone for the purpose of Russification or even restoration (software repair), as well as remove restrictions at the user or operator level (“unlock”).

Siemens x35-x45 phones

A two-wire bidirectional (FBUS) interface is required for programming. The location and purpose of the contacts in the phone connector is shown in the figure. The connector for the telephone-interface cable can be made by taking 2 connectors from the chargers. From one connector you must carefully remove the missing contacts from the first.

For programming you will need: a free COM port (RS – 232) of a computer, an interface and a telephone with a charged battery. The exchange between the computer and the phone begins either after a short press of the phone's power button (in this case the phone generates an ignition signal), or by the computer's autoignition signal, which is supplied to the phone's Charge voltage input. In general, confirmation of any operations in the program is carried out by briefly pressing the phone's power button. After connecting the computer, interface and phone, we begin the programming process.

Software structure and sources of its distribution.

For ease of understanding, software stored in a Flash memory chip can be divided into two large areas: firmware and EEPROM.
To work with the firmware area of Siemens phones, a special factory utility WinSwup was created, which allows you to completely replace both the software version and the menu language. In this case, the new version is placed in the “body” of WinSwup. Thus, as many software versions as there are WinSwups, a collection of which can be found on the portal www.allsiemens.ru/flash
In addition, it is possible to work with a custom version of WinSwup, distributed directly from the manufacturer’s official page www.benqmobile.com
In computer representation, WinSwup looks like an executable EXE file, the name of which can be represented as Name_XX_YY_ZZ.exe, Where:
Name– model of the phone for which the utility is written (may be missing) XX– software version YY– language package number (“04”, “91” - indicates the presence of Russian in the menu) ZZ– number of the T9 intuitive typing system (“05” - presence of “Russian T9”)

In the phone itself, the same information can be seen in a special service menu, called up by pressing the key combination: *#06# plus the “left selection key” (left softkey).
WinSwup cannot operate on the EEPROM memory area. If this is necessary, at your own peril and risk, you can use the freia program, with which you can work not only with EEPROM, but also with the entire firmware as a whole (fullflash).

We begin the work by setting up the Serial Config program (Figure 6), where you should specify the number of the COM port to which the interface is connected and Baud - the baud rate (usually 115200).

There are two options to start the programming process:
- If the phone is turned on and connected to the cable, press the START button.
- If the phone is turned off and connected to a cable, check the Skip box in the PreCheck position to disable phone self-testing and press the START button.

The second option is needed for cases when the phone being repaired does not turn on due to errors that could have occurred during the first option. It should be remembered that if there is no autoignition mode, after pressing the START button you need to briefly press the phone's power button.
In both cases, after completing the procedure, the program will display a message that the process was successful with 100% completion.

We start setting up the program with the Configuration functions key of the main menu - Main functions. Set COM port of cable - the number of the COM port to which the interface is connected, the exchange speed - Speed of communication (usually 115200). Then you need to specify the boot type - Boot type (“normal”) and, if autoignition is present in the interface, check the DTR box in the COM port setup menu.

Reading the firmware is carried out using the Read Flash key of the main menu - Main functions, followed by selecting a memory area in the Presets menu, which is located in the Flashing functions menu. During reading, this area is automatically saved to a file with the *.fls extension. The process is started with the OK button. The procedure is displayed in the window – Process information.

By selecting the firmware memory area, we can make and then save a complete backup of the entire phone firmware. This procedure must be carried out, first of all, in order to ensure the possibility of restoring the phone in the event of any incorrect actions. The copy may also be useful for restoring other phones in this series.

The firmware is written to the Flash memory chip using the Write Flash button of the main menu – Main functions, which opens a menu for selecting the firmware file in *.fls format that we want to write. You should be careful with the inserted files, namely, that the size of the recorded file matches the size of the memory area in which it is placed, otherwise the phone will be damaged at the software level.

Upon completion of programming, it is necessary to restore the factory phone number (IMEI) stored in the EEPROM area of the phone’s memory, since along with someone else’s firmware we also write someone else’s EEPROM, and, consequently, someone else’s IMEI. Restoration is carried out in the following order (Figure 10). Click the Unlocking functions button in the main menu – Main functions. In the Unlocking functions menu that opens, check the Direct unlock, no map is saved option and press the Use Original IMEI button. After this, we confirm the procedure by briefly pressing the power button on the phone (ignition). This operation removes user and operator encodings.

II. Connecting phone-box-computer (B- C)

Box installation

Installing drivers

1. Please do everything strictly step by step without skipping anything.

2. Do not connect the box/protection key to the computer before installing the drivers

Note:"x: " denotes the drive where Infinity-Box was installed (eg. " C:" or " D:")

W2K/XP/Vista

1. Run: x:\Program Files\InfinityBox\Drivers\Box\e-gate_W2k_XP_Vista\Setup_W2k_XP.exe or Setup_Vista.exe

2. Connect the box/dongle to the computer’s USB port. You will see 3 new devices in the system:

1. e-gate Virtual Reader Enumerators ->

2. Smart card readers ->

3. e-gate USB Smart Cards -> e-gate USB Smart Card

3. If necessary, select drivers for Unibox:

W98/ME

1. Run: x:\Program Files\Infinity Box\Drivers\Box\VC6Redist\vcredist.exe

2. Restart your computer

3. Run: x:\Program Files\Infinity Box\Drivers\Box\Smart Card Base Components\SCBase.exe

4. Restart your computer

5. Run: x:\Program Files\Infinity Box\Drivers\Box\e-gate_W98_Me\Setup.exe

6. Restart your computer

7. Connect the box/dongle to the computer’s USB port. You will see 3 new devices in the system:

1. e-gate Virtual Reader Enumerators -> e-gate Virtual Reader Enumerator

2. Smart card readers -> e-gate USB Smart card reader

3. e-gate USB Smart Cards -> e-gate USB Smart Card

8. If necessary, select drivers for Unibox: x:\Program Files\Infinity Box\Drivers\Box\FTDI

9. Restart your computer

Checking installation results

Open Device Manager and check for the following devices on your system:

Note: The COM port number may differ from that shown in the figure. Remember the COM port number and select it when using Infinity-Box programs.

When connecting your phone to the box, installing additional drivers for your phone is not required.

DICTIONARY OF SLANG AND OFFICIAL TERMS

Firmware (program, memory contents) is an array of data designed to control system components in order to implement a specific algorithm.

Firmware(process - flash, rewrite, flash) – phone software.

The term "phone firmware" refers to the process of replacing software in a cell phone. This can be done for several purposes - installing newer software, fixing software glitches, hacking the phone's security.

The firmware of the phone is carried out using special software and adapter cables between the phone and the computer, as well as boxes.

Phone software– a set of programs for the full operation of the phone. It includes an operating system and a set of so-called application programs that give the phone additional capabilities (games, music, video, Internet, etc.).

Operating system (OS)- a set of programs that ensures the execution of other (including application) programs, data input/output, data management, interaction with the operator (user), etc.

Phone programmer– a special device that is used to record information from a computer into the phone’s memory.

Switching, synchronization– communication and coordination of the phone with the computer for the purpose of data exchange.

Data cable(cable, lanyard) - a harness of wires that connects a telephone with a computer in a special way for data exchange. The connection diagram depends on the hardware implementation of a particular phone and is fundamentally different for different phones.

Interface cable - The cable is used to connect the phone to the computer. The interface cable allows you to access the Internet via your phone, send SMS, and download files.

Service cable– serves to connect the phone to a computer, has additional capabilities for programming the phone.

Shell - operating system (from the English shell - shell) - an interpreter of operating system (OS) commands, providing an interface for user interaction with system functions.

Compound- this is a raw material mixture, plastic granules with various additives that provide such qualities as frost resistance, impact resistance, non-flammability, deformation when heated, etc. Compound resin is processed according to CPU and Flash rules.

Connector(connector) – electrical connector between cable and device. A computer, charger, headphones, etc. are connected to the phone using connectors.

Interface– a set of tools and rules for the interaction of devices and (or) programs. In the simplest case, this is a matching element between the computer and the phone (external connector, data cable, programmer, infrared port, etc.).

RS232(universal interface) is a hardware and software complex that is a standard and an integral part of all computers, designed to exchange information in serial code between the computer and a wide variety of external devices.

Ignition(Ignition – “ignition”) – a signal from the phone to the computer after briefly pressing the power button on the phone (while it remains in the off state) to start the reprogramming process.

Bootloader(boot, loader, boot, loader, bootloader) – a self-booting program sent by the computer to the phone after receiving the “ignition” signal, is placed in RAM, most often the processor, and after placement it receives the rights to control the process of reprogramming (loading) the phone’s memory.

Glitch, bug, sausage– failures or incorrect operation of the phone. They occur either through the fault of the user or due to errors made during software development at the manufacturer. May appear after an incorrect software change.

Contact pad– a metallized coating on the phone circuit board for electrical connection (not soldering) of phone parts. Usually have a golden coating.

Language pack(English Language Pack) - a set of data that is part of the phone software, allowing you to use a particular language. Contains an interface language and T9 dictionaries.

HERprom(Electrically Erasable Programmable Read Only Memory)- contains the phone memory area in which the phone settings are located. That is, everything that the user changes in the phone settings is recorded here. But not all phone settings can be changed from the phone itself. It is possible to save EEprom from your phone to your computer and change some of its blocks, this will allow you to open some hidden settings items. The danger is that there are also settings for the radio path, which is calibrated at the factory once and for all for a specific phone (not even the model, but specifically for each device). To prevent troubles, it is necessary to make a backup - otherwise, in the event of an error, constant unstable communication, echo, weak signal and frequent loss of the network are inevitable.

File system,(English file system) - a regulation that determines the way of organizing, storing and naming data on storage media. It defines the format for the physical storage of information, which is usually grouped in the form of files. A specific file system determines the size of the file name, the maximum possible file size, and a set of file attributes. Some file systems provide service capabilities, such as access control or file encryption.

The file system links a storage medium, on the one hand, and an API (a set of methods (functions) that a programmer can use to access the functionality of a software component (program, module, library) to access files, on the other. When an application program accesses a file , it has no idea how the information is located in a particular file, as well as what physical type of media (flash memory block) it is recorded on. All that the program knows is the file name, its size and attributes. It receives this data from the file system driver. It is the file system that determines where and how the file will be written on the physical medium.

Test Point– (TP) is a control point responsible for sending the bootloader to the phone when the device’s software is changed. On Siemens phones of the 55th and 60th series, the circuit of this control point (pin T9 on the processor) must be open when flashing the firmware. Most often, TP is used for flashing Siemens phones, sometimes for Motorola phones. The method of working with TP is individual for each phone (cutting the track, soldering elements, shorting to ground).

Dongle(Electronic key) (also hardware key, from the English dongle) is a hardware device designed to protect software and data from copying, illegal use and unauthorized distribution.

An electronic key is a small-sized hardware device.

The basis of this technology is a specialized ASIC chip, or a specialized protected microcontroller, which has unique operating algorithms for each key. Dongles also have a small, secure non-volatile memory; more complex devices may have a built-in cryptoprocessor (for hardware implementation of encryption algorithms) and a real-time clock. Hardware keys can have different form factors, but most often they are connected to a computer via USB, LPT or PCMCIA interfaces.

IMEI- International Mobile Equipment Identifier - a number that is unique for each mobile phone released. Installed at the factory during manufacture, it serves to identify the device in the GSM network. The IMEI number can usually be read on a special plate located under the battery, and can also be determined (for most devices) by entering the following code on the keyboard:

Each mobile phone manufacturer is responsible for ensuring that no two mobile phones have the same IMEI.

The IMEI code contains 15 digits and consists of four parts:

IMEI = TAC + FAC + SNR + SP,

TAC(Type Approval Code) - a six-digit code of the selected type of phone of a specific series (the first 2 digits are the country code of the developer company)

FAC(Final Assembly Code) - a two-digit code used by the developer that can be used to determine the country where the phone was manufactured (final assembly country code)

SNR(Serial Number) - a six-digit serial code that is assigned to a specific mobile phone

SP(Spare) - one digit, depending on the manufacturer’s decision, a control or reserve number (in older models it is almost always 0).

Codes TAC And FAC may be the same for phones of the same type and the same batch, produced at the same enterprise. Code SNR always individual for each mobile phone.

Check sum - some value calculated by applying certain operations on the input data.

A checksum is usually used to verify the correctness of data transmission over communication channels or as a guarantee of the origin of certain data.

Service codes – codes and key combinations that activate system settings. For example: *#06# - IMEI of the phone.

FullFlash, (aka FF, Full) is the complete contents of the phone’s memory, which includes all other areas of the phone’s memory.

Backup- data backup. Allows you to restore data in case of data loss from your phone.

Applications:

Name, marking	Place of purchase.	Purpose
Chip MAX232	Radio parts store	RS-232 interface conversion
Microcircuit PL2303	Data cable store	COM port emulator
Equipment set Infinity PinFinder + Infinity Dongle + Unibox	Online store GSMSERVICE	For programming, Russification and unlocking
Mobile phone

In the theoretical part, I will not delve into the history of the creation of cellular communications, its founders, the chronology of standards, etc. For those who are interested, there is plenty of material both in printed publications and on the Internet.

Let's look at what a mobile (cell) phone is.

The figure shows the principle of operation in a very simplified way:

Fig.1 How a cell phone works

A cell phone is a transceiver operating on one of the frequencies in the range 850 MHz, 900 MHz, 1800 MHz, 1900 MHz. Moreover, reception and transmission are separated by frequency.

The GSM system consists of 3 main components such as:

Base station subsystem (BSS – Base Station Subsystem);

Switching/switching subsystem (NSS – NetworkSwitchingSubsystem);

Operation and Maintenance Center (OMC);

In a nutshell it works like this:

A cellular (mobile) phone interacts with a network of base stations (BS). BS towers are usually installed either on their ground masts, or on the roofs of houses or other structures, or on rented existing towers of all kinds of radio/TV repeaters, etc., as well as on high-rise chimneys of boiler houses and other industrial structures.

After turning on the phone and the rest of the time, it monitors (listens, scans) the airwaves for the presence of a GSM signal from its base station. The phone identifies its network signal using a special identifier. If there is one (the phone is in the network coverage area), then the phone selects the best frequency in terms of signal strength and at this frequency sends a request to the BS to register in the network.

The registration process is essentially an authentication (authorization) process. Its essence lies in the fact that each SIM card inserted into the phone has its own unique identifiers IMSI (International Mobile Subscriber Identity) and Ki (Key for Identification). These same IMSI and Ki are entered into the database of the authentication center (AuC) when manufactured SIM cards are received by the telecom operator. When registering a phone on the network, the identifiers are transmitted to the BS, namely the AuC. Next, the AuC (identification center) transmits a random number to the phone, which is the key to perform calculations using a special algorithm. This calculation occurs simultaneously in the mobile phone and the AuC, after which both results are compared. If they match, then the SIM card is recognized as genuine and the phone is registered on the network.

For a phone, the identifier on the network is its unique IMEI (International Mobile Equipment Identity) number. This number usually consists of 15 digits in decimal notation. For example 35366300/758647/0. The first eight digits describe the phone model and its origin. The rest are the phone's serial number and check number.

This number is stored in the phone's non-volatile memory. In outdated models, this number can be changed using special software and an appropriate programmer (sometimes a data cable), and in modern phones it is duplicated. One copy of the number is stored in a memory area that can be programmed, and a duplicate is stored in an OTP (One Time Programming) memory area, which is programmed once by the manufacturer and cannot be reprogrammed.

So, even if you change the number in the first memory area, when the phone is turned on, it compares the data in both memory areas, and if different IMEI numbers are detected, the phone is blocked. Why change all this, you ask? In fact, the legislation of most countries prohibits this. The phone is tracked online by its IMEI number. Accordingly, if a phone is stolen, it can be tracked and seized. And if you manage to change this number to any other (work) number, then the chances of finding the phone are reduced to zero. These issues are dealt with by the intelligence services with appropriate assistance from the network operator, etc. Therefore, I will not go deeper into this topic. We are interested in the purely technical aspect of changing the IMEI number.

The fact is that under certain circumstances this number may be damaged as a result of a software failure or incorrect update, and then the phone is absolutely unsuitable for use. This is where all means come to the rescue to restore IMEI and the functionality of the device. This point will be discussed in more detail in the software phone repair section.

Now, briefly about voice transmission from subscriber to subscriber in the GSM standard. In fact, this is a technically very complex process, which is completely different from the usual voice transmission over analog networks such as, for example, a home wired/radio telephone. Digital DECT radiotelephones are somewhat similar, but the implementation is still different.

The fact is that the subscriber's voice undergoes many transformations before it is broadcast. The analog signal is divided into segments of 20 ms duration, after which it is converted to digital, after which it is encoded using encryption algorithms with the so-called. public key - EFR system (Enhanced Full Rate - an advanced speech coding system developed by the Finnish company Nokia).

All codec signals are processed by a very useful algorithm based on the DTX (Discontinuous Transmission) principle - intermittent speech transmission. Its usefulness lies in the fact that it controls the telephone transmitter, turning it on only when speech begins and turning it off during pauses between conversations. All this is achieved using the VAD (Voice Activated Detector) included in the codec – a speech activity detector.

For the receiving subscriber, all transformations occur in the reverse order.

The device of a mobile phone and its main functional units (modules).

Any mobile phone is a complex technical device, consisting of many functionally complete modules that are interconnected and generally ensure the normal operation of the device. Failure of at least one module entails, at a minimum, a partial malfunction of the device, and at a maximum, the phone is completely inoperable.

Schematically, a mobile phone looks like this:

Fig.2 Cell phone device

Purpose and operation of individual nodes.

1. Rechargeable battery (AB)– the main (primary) power source of the phone. During operation, it has one unpleasant property - aging, i.e. loss of capacity, increase in internal resistance. This is an irreversible process and the rate of battery aging depends on many factors, the key of which is proper operation and storage.

Previously, the bulk of telephone batteries were produced using NiCd (nickel and cadmium based) and NiMH (nickel metal hydride) technologies. Currently, these batteries are no longer in production. With the spread of batteries based on Li-Ion (lithium-ion) technology, the latter showed the best price-quality ratio, and also had a number of advantages, in particular the absence of the so-called. "memory effect". The service life is approximately 3-4 years. Not long ago, Li-Pol (lithium polymer) batteries appeared on the market. They are cheaper than lithium-ion ones, but their service life is also shorter - about 2 years.

Modern batteries are considered operational if they retain at least 80% of their nominal capacity. In practice, there are batteries with 50% or less. That is, many users try to “squeeze” the last milliamps out of the battery, which is why they themselves then suffer, since often a worn-out battery begins to swell, which can lead to breakdowns of the phone case, and sometimes even to failure of the mains charger and circuits phone charger, power controller. So, it’s not worth saving money on batteries. The phone also needs good power

Batteries do not require special care. The main thing is to avoid hypothermia in winter (down to -10°C), because discharge and aging accelerate. As well as heating to 50-60°C and higher. This is dangerous - the battery can simply swell and even explode (this is critical for lithium batteries)!!!

A mobile phone battery consists of 2 parts: the battery itself and a small electronics-automation board.

Fig.3 Battery structure

In the picture, for clarity, I showed an already damaged swollen battery. Most often this happens as a result of the use of cheap chargers, malfunctions in the phone’s charging circuit, as well as high charging currents selected by the manufacturer (to reduce battery charging time). And, of course, cheap non-original batteries “get fat” very quickly.

As for the electronics board, it performs a protective function, preventing both the battery itself and the phone from emergency situations, such as:

Short circuit (SC) of the battery supply terminals;

Battery overheating during charging and operation;

Battery discharge is below the established minimum permissible norm;

Battery recharge;

When one of them occurs, the so-called the electronic relay and battery output terminals are de-energized.

As a rule, a modern battery has at least 3 pins for connection to the battery connector of a mobile phone. These are, respectively, “+”, “-”, and “TEMP” (temperature sensor, with the help of which the battery controller, together with the phone’s power controller, control the battery charging process, reducing or increasing the charging current, and in case of overheating or short circuit, disconnect the battery from the board terminals altogether electronics).

Fig.4 Location of battery contacts

It should be noted that the location of contacts may differ for different manufacturers!!!

The main characteristics of the battery are:

The rated voltage is usually 3.6 - 3.7 Volts. For a fully charged battery 4.2 - 4.3 Volts.

- capacity - for modern phones from approximately 700mA to 2000mA or more.

Internal resistance - the lower the better (up to about 200 milliOhms)

2. Power controller– serves to convert battery voltage into several types of voltage to power individual components and devices of the phone, such as the CPU (central processing unit), RAM and ROM (memory chips), various amplifiers, sometimes keyboard and display backlights, etc., and It also controls the battery charging process. Together with the processor, it activates the built-in or external sound amplifiers of the speaker, microphone, buzzer (polyphonic loudspeaker). Plus, it provides data exchange with a SIM card.

Structurally, it is made in the form of a separate chip. Sometimes it can be combined with a processor (Chinese fakes of well-known brands like Nokia N95, etc.)

During normal operation of the phone, the power controller rarely fails. Most often this happens during charging due to overheating or when using a non-original or faulty charger. Less often - if the phone was exposed to moisture or was hit hard.

The appearance is shown in Fig. 2 and may differ (depending on the specific phone model and its manufacturer).

3. SIM-holder (sim – connector) – SIM card holder. Based on the name, it is used to connect a SIM card to the phone. The design is almost the same for all phones, since modern SIM cards are brought to the same standard. It has 6 (rarely 8) spring-loaded contacts, with the help of which electrical communication is carried out between the SIM card and the power controller or processor. They differ only in the design of fastening (holding) the SIM card. Breakdowns include breaking off contacts when changing SIM cards frequently or ineptly (incorrectly) removing them, when the user begins to use improvised means to pick up the SIM card for further gripping with fingers and removing it from the holder. Our beautiful ladies often resort to this, using their long, expensively manicured nails. As a result, both the phone and the manicure suffer

The connector does not require special care. But there are cases (again depending on the user) when the contacts oxidize, become clogged, and lose their springy properties. In this case, VERY CAUTION is allowed!!! wipe them with an eraser (eraser) and VERY CAREFULLY!!!, slightly bend the contacts upward with a needle or wooden toothpick.

If the SIM holder (holder) malfunctions as described above, the phone will not “see” your SIM card and will constantly display a message on the display like: “Insert SIM card.” Broken holders cannot be repaired and must be replaced with new ones.

4. Microphone– serves to convert the user’s voice into weak electrical signals for the purpose of their further amplification, conversion and sending into the air. There are two types of cell phones: analog and digital. The latter have a more complex design and require more labor during dismantling and replacement.

Microphones lose their performance characteristics or fail mainly when they become dirty, exposed to water, or hit by the phone (this is especially true for digital microphones, since they themselves are very fragile).

If the microphone malfunctions, the phone may have the following defects:

The second subscriber does not hear the user at all;

The second subscriber hears the user very poorly;

A crackling sound is heard in the auditory (conversational) speaker (the so-called interference of the GSM signal). The same noise can be heard by bringing a cell phone in conversation mode or sending SMS to a working radio, amplifier, computer speakers, etc. As a rule, microphones cannot be repaired and must be replaced (except in cases of clogging of the holes and sound guides of the mobile phone case. They should simply be cleaned of dust, dirt, etc.)

5. Speaker (talk speaker)– serves to convert electrical signals into sound vibrations. That is, it works in reverse order of the microphone. One subscriber speaks into a microphone, which converts the voice into email. signals, then these signals are converted (see description above) and emitted into the air. The second subscriber receives these signals with the phone and hears them in the phone's speaker.

Most phones have several speakers installed - separately conversational and separately polyphonic. The polyphonic speaker plays a melody for an incoming call, SMS, etc. But there are phones (mostly from Samsung), where the role of conversational and polyphonic is performed by the same speaker. Only when playing a melody or other signals is the additional audio power amplifier activated. Speaker malfunctions include partial and complete malfunctions. Partial is the reproduction of speech or music very quietly, with wheezing and unpleasant ringing. This can be eliminated, but only in cases where, after an external examination, it is clear that the speaker is clogged with foreign objects. For example, such as very small metal shavings that like to penetrate through specially designated holes for the sound output of the speaker. This is due to the fact that the speaker contains a permanent magnet in its design. So he magnetizes small metal objects to himself. Personally, I am a supporter of replacing such speakers with new ones. Firstly, it will save you time that you will spend on cleaning, and you will need a lot of it. Secondly, it rarely happens that after cleaning a speaker works as cleanly, without distortion and as loudly. So, don’t think about it - immediately change it to a new one. Especially if this phone is not yours, but came for repair.

Complete – no sound at all. The reason is a break in the speaker voice coil wire. The only solution is to replace the speaker. I will write below about how to check the speaker for serviceability (integrity).

6. Speaker (buzzer, bell, polyphonic speaker - it's all the same thing)– the same speaker, only in most cases it is intended for playing ringtones, SMS, MP3, etc. But, as mentioned above, it can also be used for conversation. Malfunctions and troubleshooting methods are the same as for the earpiece speaker.

7. Central processing unit (CPU)– is the main device of a mobile phone. This is the same processor that is present in any personal computer, laptop, etc., only a little smaller and more primitive. Designed to execute machine commands, instructions and operations provided by the software (firmware) of the phone, as well as clear interaction with other modules and devices and their subsequent management. In a word, the processor is the “brain” that completely controls the operation of the mobile phone. Structurally, it is made in the form of a separate chip. Responsible for many processes that occur during normal operation of the phone. The main ones are: displaying images on the display, receiving and processing cellular network signals, receiving and processing keyboard module signals, controlling the operation of the camera, information receiving/transmitting devices, the battery charging process (together with the power controller) and much more.

Under normal phone use, the processor almost never fails and does not require any maintenance.

In modern phones, and especially smartphones (translated from English, a smartphone is a smart phone. The same phone, only it is similar to a computer due to the presence of an operating system and a variety of installed programs to perform certain tasks), 2 processors are often installed. One of them performs the same functions as in a regular phone, and the second is designed to operate the operating system and execute its programs.

If the central processor fails, the phone is completely inoperable.

8. Flash – memory. A separate chip (microcircuit) that is designed to store phone software (firmware), as well as user data (contacts, melodies, photos, etc.). Software (firmware) is a program developed by the phone manufacturer that is processed and executed by the processor. For the user, this is what he sees on the mobile phone screen and the functions that are available to him in a particular phone model.

Flash memory also rarely fails under normal use. But it should be remembered that these chips have a large, but still limited number of read/write information cycles.

Flash memory is non-volatile and retains all data written to it even after the power source (for example, battery) is turned off.

9. RAM – memory (RAM). Serves for temporary storage of data. All processor calculations of the program code are carried out in it, and the results of calculations and information processing at a specific current moment are also stored (for example, listening to music, playing videos, running applications, games, etc.) When unnecessary, the memory is cleared of some data and loads new ones and so on all the time.

It should be remembered that RAM memory (random access memory) is energy-DEPENDENT and if the power source is turned off, all data stored in RAM will be lost!!!

10. Keyboard module– a standard numeric keypad for dialing a subscriber’s number, text SMS messages + a set of additional buttons that perform functions defined by the phone software, such as adjusting the volume level, launching programs, cameras, voice recorders, etc. For normal operation of the keyboard module, the user’s main task is to keep the keyboard clean and prevent moisture, dirt and other objects from entering. Otherwise, the buttons have to be pressed with great force, or the phone does not respond to presses at all. You can restore the operation of the keyboard module by cleaning it from dirt. If the contact pads and the conductors connecting them were exposed to moisture or other liquids and were damaged, then such a key module must be replaced with a new one.

11. LCD display– the actual display (screen) of the phone. The purpose is clear to everyone, so I won’t go into depth on this. The main characteristics are the following parameters:

Resolution, that is, the number of reproduced pixels (dots). The higher this parameter, the clearer and better quality the picture will be. For more or less modern phones, the following screen resolutions are typical: 220X176 pixels, 320X240. For phones with large touch screens: 400X240, 640X360, 800X400.

Number of reproduced (displayed) colors. The same thing, the more the better. In older phones with color displays, this value is mostly 4096 colors. As it improved, this parameter increased to 65 thousand, then reached 262 thousand. Now all modern expensive phones are equipped with displays with a color depth of 16 million.

If the phone is used correctly, the display does not require any maintenance. In some cases, when the phone is used in a dusty environment or simply over time a lot of dust and debris has accumulated in the case, the display must be CAREFULLY wiped with microfiber (a special wiping cloth that cleans well and does not leave marks or streaks. It can be purchased at sales stores optics. Some types of glasses are equipped with such a cleaning microfiber.) When using the phone, do not allow physical impact on the display (impacts, squeezing, strong bends), or expose it to direct sunlight and elevated temperatures. This will lead to its failure.

12. Transceiver– used to receive and transmit GSM cellular signals. It contains many functional elements (generators controlled by the voltage of the receiver and transmitter, bandpass filters, decoupling capacitors, inductors, etc.). Controlled by a processor and a 26 MHz quartz resonator.

If the transceiver malfunctions, the phone will not be able to register in the cellular network and there will be no GSM signal strength indicator on the display.

13. Power amplifier– designed to amplify the signal generated by the transceiver to the power level required for radiation by the antenna into the air.

If the power amplifier malfunctions, the phone will receive a signal from the cellular network, but will not be able to register in it, since it will not be able to transmit a GSM signal.

14. Antenna switch (switch)– designed for pairing (connecting) the receiving and transmitting path of the GSM module to the telephone antenna. This ensures that the phone has one common antenna for reception and transmission, and also eliminates the influence of the power amplifier on the receiving path.

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 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 can 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. From one district of Moscow, subscribers began to receive complaints that they could not get through to anyone. Technical specialists began to figure it out. Most voice channels were free, but 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:

10.

11.

12.

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:

13.

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:

14.

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

15.

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

16.

24-hour monitoring of switches and controllers is carried out from the Mission Control Center of the Network Control Center (NCC):

17.

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:

18.