How it's made, how it works, how it works. Base stations of cellular operators

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 it works cellular communication…

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

After you 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 of the same cellular network, then the switch will check the Home Location Register (HLR) to find out where in at the moment the called subscriber is located (at home, in Turkey or in Alaska), and will transfer the call to the appropriate switch, from where it will forward it 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 more transmitters on 1 sector 2100 MHz - 3G network This is what a cabinet with 3G equipment looks like:

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 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 the BS with worst signal, in this 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 “upper floor problem.” 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" 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 when everyone starts congratulating each other. SMS are transmitted via service channels. On March 8 and February 23, people prefer to congratulate each other on via SMS, sending funny poems, and the phones often cannot agree with the BS on the allocation of a voice channel. I was told 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. Majority voice channels it was free, but all the staff 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. Long SMS phone divides it into several short ones and sends each separately. Employees technical service It is recommended to send such congratulations using MMS. It will be faster and cheaper. From the Base Station the call goes to the controller. It looks as boring as the BS itself - it’s just a set of cabinets:

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.

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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 the 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 own network, as well as the level of the network of colleagues from the Big Three:

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The entire roof of such a car is 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):

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(hours, days, weeks, 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 accepted by operators subscriber service. 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.

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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Plan:

1. Construction of cellular communications.

2. Structure of cellular communications.

3. History of the development of cellular communications.

Cellular communications are the most modern and rapidly developing area of telecommunications. It is called cellular because the territory in which communication is provided is divided into separate cells or cells.

As a rule, in each cell the subscriber receives the same set of services and within certain territorial boundaries receives these services at the same price. Thus, moving from one cell to another, the subscriber does not feel territorial attachment and can freely use communication services. Also important point is the continuity of the connection.

Moving the connection established by the subscriber ( voice call, packet data transmission) must not be interrupted. This is ensured thanks to the so-called Handoveu(Handover). The connection established by the subscriber is, as it were, picked up by neighboring cells in a relay race, and the subscriber continues, unsuspectingly, to talk or surf the Internet.

So, let's look at what a cellular network consists of. The entire network is divided into two subsystems: the base station subsystem and the switching subsystem.

The main elements of the base station subsystem (as you might guess) are the base stations themselves ( BTS). They create those honeycombs that were mentioned at the beginning. Each base station typically serves three cells. The radio signal from the base station is radiated through 3 sector antennas, each of which is aimed at its own cell. Sometimes you can encounter a situation where several antennas of one base station are directed at one cell at once. This is due to the fact that the cellular network operates in several bands (900 and 1800). In addition, a given base station may contain equipment from several generations of communications ( 2G And 3G).

The most common location for a base station is a tower or mast built specifically for it. However, in urban areas it is difficult to find a place to place a massive structure. Therefore, in large cities, base stations are located on buildings. In addition, in lately appear mobile options base stations located on trucks. They are very convenient to use during natural disasters or in places of mass gatherings of people (football stadiums, central squares) during holidays, concerts, football matches. But, unfortunately, due to problems in legislation, they have not yet found wide application.

Base station on the tower

Base station on the roof of a building

Mobile base station

Oddly enough, cellular operators often allow their competitors to use their tower structures to place antennas (On mutually beneficial terms, of course). This is due to the fact that building a tower or mast is an expensive proposition, and such an exchange allows you to save quite a bit of money!

From the base station subsystem, the signal is transmitted towards the switching subsystem, where a connection is established in the direction desired by the subscriber. The switching subsystem has a number of databases that store subscriber information. In addition, this subsystem is responsible for security.

We looked at the main elements of a cellular network. Here the terms of the standard were specifically used GSM. However, both previous and subsequent standards contain similar elements and functions, only under different names

Radio communications are organized not only using fixed radio networks, but also using networks with mobile objects (SNPO).

A radio communication network with mobile objects is a set of technical means that can be used to provide mobile objects with communication between themselves and with subscribers. telephone network. It is designed to serve subscribers during international, national and regional movements (roaming) and allows for communication between subscribers when they cross the borders of different geographical zones.

Radio communication networks with mobile objects are classified according to several criteria (Fig. 3.8). Technological PSPOs belong to certain departments and services (gas industry, railway transport, ambulance, fire protection, etc.). They are intended to provide radio communication services to a limited number of individuals and legal entities.

Classification of radio communication networks with mobile objects

Technological DSPOs are divided into dispatching, trunking and radio data transmission networks. Dispatch control systems are designed for radiotelephone communication between government officials and subordinate mobile objects, as well as between subscribers.

Cellular PSPOs refer to public terrestrial radio communication networks with mobile objects that provide subscribers with all types of regular services. telephone communication. They are built as a set of networks covering the service area, in which frequency reuse is used to ensure efficient use of the allocated frequency resource and high network capacity.

Trunking (radial and radial-zone) networks are designed to provide communication services mainly to subscribers of departmental networks based on the implementation of multi-station access to a small number of radio channels with limited or no access to the public telephone network. Trunking networks make it possible to replace radio communication networks with a fixed frequency allocation and to integrate various user groups within one communication network in order to increase the efficiency of using the radio frequency spectrum.

From a topological point of view, a cellular network is built in the form of a collection of cells, or cells, covering the service area. General structure a cellular radio communication network with mobile objects is shown in Fig. 3.9.

Structure of a cellular radio network

The cellular network structure is based on the principle of frequency reuse - the main principle of the cellular network. Elements of the cellular network, in addition, are:

– switching center;

– base stations;

– mobile stations, or subscriber radiotelephone sets.

A cellular base station (BS) serves all mobile stations within its cell, while the base station provides the resource for establishing connections at the request of mobile subscribers, usually on an equal basis.

When a subscriber moves from one cell to another, his service is transferred from one base station to another. All base stations of the network, in turn, are connected to the switching center, from which there is access to the unified telecommunications network of the Russian Federation.

Currently, the pan-European standard GSM-900 is widely used. In this standard, mobile station transmitters operate in the frequency range 890–915 MHz, base station transmitters operate in the frequency range 935–960 MHz. A constant spacing of 45 MHz is provided between the receive and transmit bands. Each of the subranges is divided into 124 frequency channel in 200 kHz steps. The maximum communication range is 35 km.

The GSM standard ensures a high degree of security for transmitted messages due to their encryption using a public key encryption algorithm. Functional interconnection of system elements is carried out by a number of interfaces.

The technology for constructing trunking communications uses the principle in which a specific channel is assigned for each communication session individually depending on the load distribution in the system, and the load traffic is mainly closed within the networks. Subscriber access to the public telephone network (PSTN) is limited.

Currently, radial and radial-zone trunking networks are used. Such a network includes:

– a base station consisting of an antenna-feeder device, transceiver modules, controllers for each transceiver module and a base controller;

– zone equipment (station), consisting of autonomous repeaters, connecting lines to the public network and controllers;

– control equipment, consisting of a system terminal “system manager”, dispatcher consoles.

In trunking networks built on the radial principle, the entire channel resource is assigned to one central base station (CBS). The antenna of such a station is located at the highest point of the proposed service (Fig. 3.10. An example of such an architecture is the Soviet radio communication network Antey, created in 1960.

Structure of a trunking network built on a radial principle

The scheme under consideration has a number of disadvantages, in particular, to expand the service area it is necessary to increase the power of the subscriber station (SS), which accordingly increases the overall level of interference.

If not large quantities subscribers, an increase in the service area can be achieved using the radial-zone principle. A so-called single-cell network is being formed with several antenna locations and broadcasting on a common wavelength. In this case, along with the main antenna placement point (UKS), there are a number of auxiliary points (AS), connected by communication lines to the main one (Fig. 3.11).

Structure of a trunking network built on the radial-zone principle

In general, the technology for building trunking networks provides for the following:

– using the method of freely selecting an unoccupied radio access channel from a channel bundle allocated in each service area. This is achieved by creating a common service (signaling) channel for all users in each zone, through which call signals are sent to the corresponding base station, including the identification of the called subscriber, as well as the calling subscriber number;

– they do not provide continuous communication when subscribers cross the boundaries of radio coverage zones of base stations. “Handover” has been replaced by the operation of re-entering the network when the quality of communication deteriorates due to the user moving from one zone to another;

– empowering base stations with local cell management functions by directly connecting subscribers located in the coverage area through a local switch, as well as connecting mobile users to a local automatic telephone exchange (PBX), which has direct outputs to the local switch of the base station or through a control center.

The issue of base stations has already been raised, but a clear definition has not been identified. I believe that these towers should be removed, because they do not serve any purpose. useful information, and when there are a large number of them (towers), it only litters the map.

akbars, please write a clear definition of what needs to be done with them. And it is advisable to include it in the rules.

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The issue of base stations has already been raised, but a clear definition has not been identified. I believe that these towers should be removed, because they do not carry any useful information, and if there are a large number of them (towers), it will only litter the map.

akbars, please write a clear definition of what needs to be done with them. And it is advisable to include it in the rules.

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Today in our country almost everyone uses mobile communications, but not everyone understands exactly how it functions. About what mobile communications and this is, first of all, a network of base stations; we only think about it when we notice one of these objects near our home or office.

A significant number of base stations and the lack of reliable information regarding the installation and operation of BS are becoming causes of public concern. After all, the lack of information, as we know, instantly gives rise to rumors, speculation and myths, resulting in panic and radiophobia - fear of possible negative radiation from base stations. So let's figure out what a base station is.

A base station is a complex of radio transmitting equipment (repeaters, transceivers) that communicate with the end user device - a cell phone. One base station GSM standard usually capable of supporting up to 12 transmitters, and each transmitter is capable of simultaneously communicating with 8 communicating subscribers. The coverage area from the base station antennas forms a cell, or group of cells. Base stations connected to the cellular network switch via a base station controller.

Base stations of cellular operators BS are transceiver radio engineering objects operating in the UHF range (300-3000 MHz). In addition, each BS is additionally equipped with a set of transmitting and receiving equipment radio relay communication, operating in the range of 3-40 GHz, responsible for the integration of this BS into the network as a whole. The power of BS transmitters usually does not exceed 5-10 W per carrier.

Basically, two types of BS transmitting (receiving) antennas are used:

weakly directional with pie chart directivity (DP) in the horizontal plane - "Omni" type and directional (sector) with the opening angle (width) of the main lobe of the pattern in the horizontal plane, usually 60 or 120 degrees

Is cellular communication harmful?

Currently, only the indirect harm of cellular antennas installed in populated areas has been reliably confirmed. German scientists tested the operation of 231 models of pacemakers when exposed to electromagnetic radiation from cellular communications standards NMT-450, GSM 900 and GSM 1800. According to the results of their study, more than 30% of cardiac devices experience interference from phones operating in the NMT-450 and GSM 900 standards There was no effect of GSM 1800 phones on pacemakers.

The radio frequency (RF) range of electromagnetic fields in which modern cellular communications operate ranges from 450 MHz to 1.9 GHz. When discussing possible adverse health effects from exposure to RF fields, it must be emphasized that such fields, unlike ionizing radiation (gamma, X-rays, short-wave ultraviolet), regardless of their power, cannot cause ionization or secondary radioactivity in the body.

A proven effect of RF waves with a frequency above 1 MHz is the heating of tissues due to their absorption of EMF energy. High intensity fields are capable of locally increasing tissue temperature by 10 °C. Even a less significant change in the temperature of living tissues can lead to consequences such as impaired fetal development, decreased male fertility, and changes in hormonal levels. According to the WHO, heating caused by RF fields with an intensity that meets international standards for cell phones and base stations, is leveled out due to the normal thermoregulation of the body and cannot cause any pathological changes in cells.

Experiments on cats and rabbits have shown that low-intensity RF fields, without causing tissue overheating, are able to modulate the activity of nerve cells by changing permeability cell membranes for calcium ions, which can negatively affect the functioning of the central nervous system. There is also evidence of the ability of RF fields to increase the rate of proliferation, change enzymatic activity and affect the DNA of cells.

The described effects of EMF have been studied in animals for more than half a century, but their consequences for human health remain unclear. According to Mike Repacholi, coordinator of the WHO Committee on Radiation and Protection of Human Health and the Environment, there is no reliable evidence yet harmful effects mobile communications on human health.

SAR - specific absorption rate

Today, world standards regulating the safety of cell phones characterize the level of radiation with the SAR parameter (Specific Absorption Rates), which is measured in watts per kilogram. This value determines the electromagnetic field energy released in tissues in one second.

In Europe, the permissible radiation value is 2 W/kg. In the USA, the restrictions are more stringent: the Federal Communications Commission (FCC) certifies only those cellular devices whose SAR does not exceed 1.6 W/kg. This level of radiation does not lead to significant heating of tissue, say experts from the Finnish Center for Radiation and Nuclear Safety. As previously reported, a study conducted at this scientific institute showed that SAR level for 28 tested phone models it ranges from 0.45 to 1.12 W/kg.

In Russia, the permissible intensity of electromagnetic fields is regulated by sanitary rules and regulations. The restrictions imposed by SanPiN are measured in fundamentally different units compared to the global ones - watts per square centimeter, while determining the energy “entering” the tissue in one second. Moreover, electromagnetic waves, depending on their frequency and the type of living tissue with which they interact, will be absorbed differently.

SanPiN standards cannot be converted into SAR units by simple calculations. In order to determine the compliance of a new cell phone model with Russian standards, it is necessary to carry out laboratory measurements. Experts note that Russian requirements actually set more stringent limits on the power of cell phone transmitters than recommended by World Health Organization (WHO) standards. However, according to WHO, such an increase in standards does not have any scientific basis.

Mobile phones emit less than normal

A study conducted by Finnish scientists showed that the radiation of the most popular mobile phones in the world today approximately coincides with the level declared by the manufacturers, and is much lower than permissible standards.

The annual report of the Finnish Radiation and Nuclear Safety Center (STUK) examines 16 new mobile phone models from the world's leading manufacturers, including local company Nokia, American Motorola, South Korean Samsung Electronics, Swedish-Japanese Sony Ericsson and German Siemens. According to Reuters, the Center's previous report, released in 2003, looked at 12 phone models.

The radiation of all considered mobile phone models was significantly lower than the so-called specific coefficient absorption rate (Specific Absorption Rate, SAR), the permissible value of which in Europe is 2 watts/kg. This level of radiation does not lead to significant heating of tissues or any other negative consequences for human health, say STUK experts. They say SAR levels in all 28 models tested to date range from 0.45 to 1.12 watts/kg.

At the end of 2004, the results of a four-year study funded by the European Union called Reflex were released. Despite the conclusion that electromagnetic radiation within the SAR range of between 0.3 and 2 watts/kg damages DNA in the laboratory, scientists have not been able to definitively prove that mobile phones pose a threat to human health in real life. They believe that such conclusions require further research outside the laboratory - on animals and human volunteers.

There is no clear scientific evidence that mobile phones are harmful, but every day there is more and more evidence that they do pose a threat to human health. Thus, new data published by Irish doctors indicate that in this country every twentieth resident has already become a victim of radiation from mobile phones. Symptoms of overexposure, according to Irish experts, are: fatigue, confusion, dizziness, insomnia or sleep disturbances, nausea, skin irritation. According to Irish doctors, similar symptoms have been reported in most countries where mobile communications have become widespread.

The results of other similar studies are also quite alarming. Thus, it was reported that mobile phones can provoke asthma and eczema, destroy blood cells and harm men's health. The danger that a mobile phone poses to the developing body of children is currently little disputed - it has come to the point that the sale of mobile phones designed specifically for children has been stopped in the UK.

“It is also important that future radiation standards for mobile phones and base stations are based on the most up-to-date and scientifically proven evidence of the health effects of radiation,” says Kari Jokela from STUK. Finnish scientists note, however, that some of the Center's studies have revealed some signs that microwave radiation from phones can cause slight changes in the functioning of cells, but these facts are not enough to draw conclusions about the impact of cell phone radiation on human health.

As is known, the coverage of any cellular network is a cellular (cellular) structure formed with the help of (BS). Each base station can serve one or more, depending on the network configuration and the need for capacity and quality of coverage in a given area. In the most general case, base station equipment can be divided into 3 components: transceivers, antenna-feeder device (AFD) and auxiliary equipment (air conditioning, power supply, fire extinguishing systems, security complex, etc.). Possible ways There are countless implementations. Depending on the generation, capacity, standard used, coverage area, the BS can be made either in a free-standing container in combination with a 72-meter mast, or in the form of a small compact case for coating inside buildings -. Let's consider the most typical cases of implementing full-scale BS for coverage both in urban conditions and outside the city.

The most typical way of placing BS equipment is to install a special or, at the foot of which there are one or more containers for transceiver equipment. The main purpose of installing an antenna-mast structure is to place an antenna-feeder device. It includes a set of antennas to create radio coverage of an omnidirectional, but more often sectoral type, as well as feeders that connect the antennas to the transceiver equipment. In addition, in rural areas, signal amplifiers in the uplink direction (low noise amplifiers) are often used together with antennas, which expand the coverage area. The tower is also necessary to accommodate transport equipment if RRL (radio relay communication lines) are used. They usually include a directional parabolic antenna, a radio module that converts low frequency signal into a high-frequency one for transmission to the remote side and a separate feeder that transmits a low-frequency signal from the BS equipment or a separate transport module inside the equipment room.

The container holds transceivers, transport equipment, as well as equipment designed to ensure uninterrupted operation and safety. Transceiver equipment usually combines a control unit, transceivers (TRX) and combiners that combine the radio signal from various antennas and TRX in different configurations. The equipment room may contain equipment operating in several frequency ranges or even different standards and generations ( and ). At BSs located far from large populated areas, they are usually used to form transport channels to the base station controller. However, in some cases, electrical wire lines or satellite communications are used. An integral element of the BS equipment is the power supply system. Usually this is a special source DC 48V, tangleable alternating voltage 220 or 380V. It also switches to the battery ( batteries) in the event of a loss of external power and ensure their recharging - after resumption. Any hardware BS is equipped with a system for maintaining operating temperature and air humidity values. Typically this is a split system, one or two operating either alternately or as active/standby. Typically, any high-rise structure must be marked with special obstruction lights to ensure its detection by aviation pilots in poor visibility conditions or at night. Therefore, in the equipment room you can also find an additional power source and a set of batteries to power the tower lighting system.

Separate towers are rarely installed for placement in cities, because it is both expensive and ineffective. Therefore, antennas are usually installed on residential and industrial buildings and structures, as well as chimneys and other existing tower-type structures. The main requirement is that the location complies with all hygienic standards for the installation of such objects. This method of placing equipment usually does not change the composition of the BS. In this case, the container is usually replaced by a partition in the attic or technical floor or a separate room in the building, and antennas and feeders are often disguised as the appearance of the building so as not to spoil its appearance.

In addition to the container method of placing equipment, many manufacturers offer to install special outdoor ones. Their placement does not require a separate room, and all equipment is placed in special thermal boxes and can be mounted in any convenient place: wall, roof, attic, etc. This significantly saves the company's operating costs. However, the main disadvantage of such BSs is their low capacity and the difficulty of expanding their capacity. Therefore, they are not used as widely as with a container.

Also, recently, many manufacturers have offered so-called. In this case, the transceiver equipment is divided into two parts: one is installed in a container and serves as the main control and signaling processing unit, and also provides interfaces to the base station controller. The other part is installed in close proximity to the antennas and converts the signal received from the control unit into a high-frequency radio signal transmitted to the antennas via feeders. Both parts are usually connected to each other using an optical patch cord or, less commonly, a twisted pair cable. At the same time, savings on the length of the feeder can reach tens of times, which accordingly significantly reduces attenuation and simplifies installation. This scheme has become especially widespread for the implementation of BS.