How does the mobile communication (23 photos + text)

A large area populated part of the country is covered by a base station (BS). In the field, they look like the red and white tower, and the city hidden on the roofs of residential houses. Each station catches the signal from the mobile phone at a distance of 35 kilometers and communicates with a mobile phone on business or voice channels.







Once you dial another, your phone is associated with your nearest base station (BS) for service channel and requests that the voice channel. The base station sends a request to the controller (BSC), and forwards it to the switch (MSC). If your friend is a subscriber of the same network, the switch check with the Home Location Register (HLR), to find out where is currently the caller (at home, in Turkey or in Alaska), and transfer the call to the appropriate switch from the one it will forward to the controller and then to the base station. The base station will be contacted with a cell phone and connect you to the other. If your friend is a subscriber of another network or you call on the telephone, then your switch Refer to the appropriate switch on another network.

Difficult? Let's look in more detail.

The base station consists of a pair of iron cabinets, locked in a well-conditioned space. Given that Moscow was on the street 40, I wanted to live in this little room. Typically, the base station is either in the attic of the building, or in a container on the roof:




Base station antenna is divided into several sectors, each of which is "light" in their favor. Vertical antenna communicates with the phone, round the base station connects to the controller:




Each sector can support up to 72 calls simultaneously, depending on the setup and configuration. Base station 6 may consist of sectors, thus, one base station can handle up to 432 calls, however, are usually found at the station transmitters and a smaller number of sectors. Mobile operators prefer to put more BS to improve the quality of communication.

The base station can operate in three ranges:

900 MHz - signal at that frequency spreading further and better penetrates buildings
1800 MHz - signal travels shorter distances, but allows you to install more transmitters on one sector
2100 MHz - Network 3G

Here is the case with 3G equipment:




At the base station in the fields and villages set transmitters 900 MHz, and in the city, where the base station as a needle stuck in hedgehog mainly for communication is 1800 MHz, although any base station transmitters may be present all three bands simultaneously.





900 MHz signal can beat up to 35 kilometers, although the "range" of some base stations standing along the trails can be up to 70 kilometers, by reducing the number of concurrent users on the station twice. 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 in such a way as to provide optimal coverage of the radio signal at the ground level. Therefore, despite the distance of 35 kilometers, to the height of the flight of aircraft radio just is not sent. However, some airlines have begun to be installed on their aircraft low-power base stations that provide coverage inside the aircraft. This connects the BS with the terrestrial cellular network via satellite channel. The system is complemented by a control panel that allows the crew to turn on and off the system, as well as certain types of services, such as voice off on night flights.

Telephone can measure the signal strength from 32 base stations simultaneously. Information on the 6 best (in terms of the signal) it sends to the service channel and have the controller (BSC) decides what the BS transmits the current call (Handover), if you are on the move. Sometimes the phone can make a mistake and throw you to the BS with the worst signal, in this case, the conversation may be interrupted. It may also be that at the base station, which was chosen by your phone, all the voice lines are busy. In this case, the conversation is interrupted as well.

I also spoke about the so-called "problem of the upper floors." If you live in a penthouse, sometimes, during the transition from one room to another, the conversation may be interrupted. This occurs because the phone in one room can "see" the BS, and the second - the other, if it comes to the other side of the house, and at the same time, these two base stations are at a great distance from each other and are not registered as " neighbor "in the cellular operator. In this case, transfer a call from one BS to another will not occur:


Feedback is provided to the subway as well as on the street: Base Station - Controller - switch, with the only difference being that there is little used by the base station and the tunnel cover is provided not a conventional antenna, and special radiating cable.

As I wrote above, a BS can produce up to 432 calls simultaneously. Usually this power enough for the eyes, but, for example, during some holidays BS can not cope with the number you wish to call. Usually this happens on New Year's, when all begin to congratulate each other.

SMS are sent by official channels. On March 8 and 23 February people prefer to congratulate each other via SMS, sending funny poems, and phones often can not agree with the BS to allocate a voice channel.

I was told an interesting case. From one area of ​​Moscow began to receive complaints from customers that they can not reach anywhere. Technicians began to understand. Most voice channels were available, and all service were occupied. It turned out that next to this BS was an institution in which students and examinations were constantly exchanged text messages.

Long SMS phone divides into several short and sends each separately. Technical Staff are advised to send such greetings via MMS. It will be faster and cheaper.

From the base station gets the call to the controller. It looks as boring as BS itself - it's just a set of cabinets:



Depending on the equipment, the controller can handle up to 60 base stations. Communication between the BS and the controller (BSC) can be carried out by radio relay channel or optics. The controller manages the operation of radio stations, including controls the movement of the called party, transmitting a signal from one BS to another.

Looks much more interesting switch:





Each switch serves between 2 and 30 controllers. He has been a great room, cluttered with various equipment cabinet:







The switch controls the traffic. Remember the old movies where people first dial up "girl" and then she had to connect them to the other party, peretykivaya wiring? The same deal and modern switches:



To monitor the network at Beeline have several cars that they affectionately called "hedgehogs". They move around the city and measure the signal strength of its own network, as well as the level of a network of colleagues from the "Big Three»:



The entire roof of the vehicle studded with antennas:



Inside equipment worth performing hundreds of calls and read information:



Convenience control switches and controllers is carried out from the Mission Control Center Network Control Center (SCC):



There are 3 main areas to control the cellular network: accident statistics and feedback from subscribers.

Just as in the aircraft, all the network equipment are sensors that send a signal to the MSC and outputting the information to the computer controllers. If a piece of equipment breaks down, then the monitor will "flash light".

CFB also tracks statistics on all the switches and controllers. He analyzes it, comparing with the previous period (hour, day, week, etc.). If the statistics of some of the nodes has become dramatically different from the previous indicators, the monitor will again be "flashing light».

Feedback received by the operators of Customer Service. If they can not solve the problem, the call is transferred to a technician. If he is powerless, the company created an "incident" that decide engineers engaged in the operation of the relevant equipment.

For switches clock watch on 2 Engineer:



The graph shows activity in Moscow switches. It is clearly seen that night almost nobody calls:



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




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