Cellular communication is... The principle of cellular communication

What is cellular communication? It is a system that uses a large number of low-power wireless transmitters to create cells—the primary geographic coverage area of ​​a wireless communications system. Variable power levels allow cell sizes to be tailored to subscriber density and region-specific needs.

As mobile users move from cell to cell, their conversations are “handed off” between these zones to ensure uninterrupted service. Channels (frequencies) used in one such unit can be reused in another at some distance.

Cellular communication is...

Cellular refers to Advanced Mobile Phone Service (AMPS), which divides a geographic region into sections called cells. The purpose of this division is to make maximum use of the limited number of transmission frequencies.

Cellular communication is a form of communication technology that enables the use of mobile phones.

A mobile phone is a two-way radio that allows simultaneous transmission and reception.

Cellular mobile communications are based on geographical division of communication coverage area. Each cell is allocated a certain number of frequencies (or channels), which allow a large number of subscribers to simultaneously carry out conversations.

A common element of all generations of mobile communication technologies is the use of certain radio frequencies (RF), as well as the reuse of frequencies. This makes it possible to provide services to a large number of subscribers while simultaneously reducing the number of channels (bandwidth). It also allows for the creation of wide networks, fully integrating the advanced capabilities of the mobile phone.

Increased demand and consumption, as well as the development of various types of services, have accelerated the rapid technological development of modern networks, as well as the continuous improvement of cellular devices themselves.

Pros and cons of Samsung phones

New modern models are constantly appearing in smartphone lines. The company makes sure that its gadgets meet the latest trends in the development of modern technologies. Let's look at the pros and cons of Samsung phones.

Pros:

1. High quality build.
2. Bright, energy-saving Amoled display.
3. Interesting new functionality: fingerprint detector, voice control, face recognition, etc.
4. High level of service.
5. Differentiation of phones by line: budget, middle class, flagships.

Minuses:

1. High cost of devices.
2. Expensive repairs if replacement is carried out with original parts.
3. Over time, Amoled displays burn out.
4. Constantly released operating system updates eventually become irrelevant for older devices, so you have to change your phone to a more modern one.

How mobile communication works

Each mobile phone uses a separate temporary radio channel to communicate with the cell site. This site supports communication with many phones simultaneously, using one channel per phone. The channels use a couple of cellular frequencies:

1. Direct line for transmission from a cell site.
2. A reverse line so that the cell site can receive calls from users.

Radio energy dissipates over distance, so cell phones must remain close to the base station to maintain communication. The basic structure of mobile networks includes telephone systems and radio communication services.

Advantages and disadvantages of a shockproof phone

There is a whole line of super-stable models of devices that are designed for active people. Let's look at the pros and cons of using a mobile phone, which has several levels of protection.

Pros:

1. Durable case made of shockproof material.
2. Moisture-resistant or waterproof.
3. Durable tempered glass display.

Minuses:

1. Design.
2. Limited functionality.
3. Bulky dimensions.

Shockproof phones are able to maintain their working condition even after falling down from a multi-story building, but in terms of design and functionality they are clearly inferior.

How cellular communications work (for dummies)

The process begins by activating the chip by entering the PIN code of the inserted SIM card. Then the cellular signal is transmitted via control channels. The response from the called number is transmitted over a free control channel to the base station antenna, from where it is transmitted to the mobile switching center.

The switching center searches for the base station with the maximum signal strength of the cellular subscriber's cell phone and switches the conversation to it.

How is data transferred?

Radio channels utilize the transmission medium efficiently through the use of the following multiple access and multiplexing schemes:

• Frequency Division Multiplexing (FDMA);
• Time Division Management (TDMA);
• code division (CDMA);
• with spatial division (SDMA).

Small cells, which have a smaller coverage area than base stations, are classified as follows:

• Microcell - less than 2 kilometers.
• Picocell - less than 200 meters.
• Femtocell - about 10 meters.

What is cellular communication for children? This term usually refers to special “children’s” tariffs with special service packages.

Early telephone system architecture

Traditional mobile service was structured similarly to television radio broadcasting: one very powerful transmitter, located at the highest point in an area, would broadcast over a radius of up to fifty kilometers.

The cellular concept structured the telephone network differently. Instead of using a single high-power transmitter, many low-power transmitters were placed throughout the cellular coverage area.

For example, by dividing an area into one hundred different areas (cells) with low-power transmitters using twelve conversations (channels), the system capacity could theoretically be increased from twelve conversations or voice channels using one high-power transmitter to twelve hundred conversations (channels). ), using hundreds of low-power transmitters.

The urban area is configured as a traditional mobile phone network with a single high-power transmitter.

Mobile communication system using cellular concept

Interference problems caused by mobile devices using the same channel in adjacent areas have proven that all channels cannot be reused in every cell. Although this affected the effectiveness of the original concept, frequency reuse has become a viable solution to the problems of mobile telephony systems.

Engineers discovered that the impact of interference was not related to the distance between zones, but to the ratio of the distance to the power (radius) of the zones' transmitters. By reducing the zone radius by fifty percent, service providers can quadruple the number of potential customers in the zone.

Systems based on areas with a radius of one kilometer will have one hundred times more channels than systems with areas within a radius of ten kilometers. Speculation led to the conclusion that by reducing the zone radius to a few hundred meters, millions of calls could be handled.

The cellular concept uses variable low power levels, allowing cells to be selected according to subscriber density and the needs of a given area. As the population grows, cells can be added to accommodate this growth.

Cellular frequencies used in one cluster of cells can be reused in other cells. Conversations can be transferred from cell to cell to maintain constant telephone communication as the user moves between them.

Cellular radio equipment (base station) can communicate with mobile phones as long as they are within range. Radio energy dissipates over distance, so mobile phones must be within the operating range of the base station. Like the early mobile radio system, the base station communicates with mobile phones through a link.

A channel consists of two frequencies: one for transmitting to the base station and one for receiving information from the base station.

Operating principle

Cellular networks exploit the ideas of media access control (MAC). Complete analogue of the wired version. Data is multiplexed, saving resources. The physical environment determines the specific protocol design. The radio signal changes due to optical effects, weather conditions, time of day, and year. The reception quality is constantly fluctuating. The obvious solution is to increase the power, but this measure also increases the interference phenomenon. The number of errors is growing. Approximate ratios:

1. Wired network – the number of errors is less than a millionth.
2. Cellular communications - the number of incorrect packets is over a thousandth.

The difference exceeds three orders of magnitude. Terminals have to use half-duplex mode. The energy of the transmitted packet is much higher than the received signal. Features of the circuitry allow interference. The leakage of so much power into the reception path of a full-duplex device interferes with the decryption of packets.

Controlled Access Scheme

An operations controller is appointed to coordinate the distribution of resources. More often the role is played by a tower, an access point. The terminal executes a pre-programmed program for allocating channels, frequencies, time slots, and antennas. No conflicts are guaranteed.

Cellular system

1. TDMA. Time division.
2. FDMA. Division by frequency.
3. OFDMA. Orthogonal frequency access.
4. SDMA. Spatial division.
5. Poll.
6. Token Ring.

Dynamic resource allocation brings undeniable benefits to heavily loaded networks. Because free access protocols spend the lion's share of time preventing collisions. The terminal checks the activity of subscribers one by one, using random number algorithms, providing slots for those wishing to transmit information.

A common disadvantage of controlled access schemes is the difficulty of covering extended areas with cells. Service information packets take up a lot of space.

Frequency division

Evolutionarily oldest cellular technology. Within a session, a request receives a unique frequency. An empty channel is marked with an appropriate identifier, allowing further distribution of the resource.

The method is used in narrowband systems, where the length of a symbol significantly exceeds the average message delivery time. Variable bitrate requires modification of the method, allocating a band according to the width of the signal spectrum. But frequency division will allow you to organize a duplex channel.

Time division

The controller allocates a fixed time interval to the subscriber. Without taking into account the slot load.

Multiplexing by signal spectrum width

The circuit combines time division and frequency division. There are 2 daughter species:

1. Pseudo-random restructuring. Current frequency and time channels are composed of a strip of narrow segments. A subscriber broadcasting a narrowband signal receives a slot. The entire time is allocated, the frequency is allocated free (can change) at the current moment. The frequency change can occur several times during the duration of one bit of information.
2. Direct sequence method. The bit is encoded by a pseudo noise signal (PNS) modulating the carrier. The spectrum is greatly expanded, allowing for a lower signal-to-noise ratio. This eliminates mutual interference between terminals and reduces power density. The use of PSN allows several subscribers to operate a single frequency.

Orthogonal frequency division

The electronic filling of the receiver performs the inverse Fourier transform of the signal. The spectrum arrives in parts, transmitted by spaced carriers. The parallel use of several narrow channels provides a chance to improve resource utilization.

Free access protocol

The terminal provides resources randomly. Lack of coordination implies the occurrence of collisions. Ideal choice for low-load networks. Otherwise, system performance drops sharply. But the hardware implementation is extremely simple.

1. ALOHA.
2. CSMA.
3. CSMA/CA.

Cellular System Architecture

Increased demand and poor quality of existing services have prompted mobile service providers to explore ways to improve service quality and support more users on their systems. Since the amount of frequency spectrum available for mobile cellular use was limited, efficient use of the required frequencies was necessary for communications coverage.

In modern cellular telephony, rural and urban areas are divided into districts according to specific service rules. Deployment parameters, such as number of divisions and cell sizes, are determined by engineers experienced in cellular system architecture.

Provision for each region is planned according to an engineering plan that includes cells, clusters, frequency reuse and handover.

A cell is the basic geographic unit of a cellular system. These are base stations that transmit signals across small geographic areas, which are represented as hexagons. The size of each varies depending on the landscape. Due to limitations imposed by natural terrain and man-made structures, the true shape of the cells is not a perfect hexagon.

A cluster is a group of cells. No channel is reused across the cluster.

Since only a small number of radio frequencies were available for mobile systems, engineers had to find a way to reuse radio channels to carry more than one conversation at a time. The industry's solution was called frequency scheduling or frequency reuse. Frequency reuse was realized by restructuring the mobile phone system architecture into a cellular concept.

Cellular standards are as follows: The concept of frequency reuse is based on assigning each cell a group of radio channels used within a small geographic area. Cells are assigned a channel group that is completely different from neighboring similar units. Their coverage area is called a fingerprint. This fingerprint is bounded by a boundary so that the same group of channels can be used in different cells that are far enough apart that their frequencies do not interfere.

Cells with the same number have the same set of frequencies. If the number of available frequencies is 7, the frequency reuse ratio is 1/7. That is, each cell uses 1/7 of the available cellular channels.

Generations of communication

The development of the industry proceeded in pronounced waves. The term generation caught up with the race at the 3G stage. Now the word is used retrospectively, reviewing past achievements.

1G – analog cells

The concept was launched (1979) by the Japanese Nippon Telegraph and Telephone Company (NTT), covering metropolitan Tokyo. Having fulfilled the five-year plan, the engineers covered the islands of the archipelago with a net. 1981 is considered the year of birth of the Danish, Finnish, Norwegian, Swedish NMT communication systems. A single standard helped implement international roaming. The USA waited 2 years, seeing European successes. Then the Chicago provider Ameritech, using Motorola devices, began to capture the market. Similar steps followed from Mexico, Canada, Great Britain, and Russia.

North America (October 13, 1983 - 2008), Australia (February 28, 1986, Telecom), Canada widely used AMPS; UK – TACS; West Germany, Portugal, South Africa – S-450; France – Radiocom 2000; Spain – TMA; Italy – RTMI. The Japanese produced standards incredibly quickly: TZ-801, TZ-802, TZ-803. Competitor NTT created the JTACS system.

The standard includes a digital call to the station, but the transmission of information is completely analog (modulated UHF signal above 150 MHz). Encryption was completely absent, filling the pockets of private detectives with coins. Frequency division of channels left room for illegal cloning of devices.

Cellphone DynaTAC 8000X Ameritech

On March 6, 1983, the development of the DynaTAC 8000X Ameritech mobile phone was launched, costing the company a fortune. For a whole decade, the device struggled to reach store shelves. The list of people willing to subscribe numbered in the thousands, despite obvious shortcomings:

• Battery life.
• Dimensions.
• Fast discharge.

The phone generation was later successfully upgraded, providing an upgrade to the 2G generation.

2G – digital communication

The emergence of the second stage of development marked the beginning of the 90s. Two main competitors immediately emerged:

1. European GSM.
2. American CDMA.

Key differences:

1. Digital transmission of information.
2. Out-of-band telephone tower calling.

The 2G era is called the era of custom phones. There are too many buyers; the manufacturer collected lists of those interested in advance. Finland was the first to launch the Radioliniya network. European frequencies are historically higher than US frequencies, with some 1G and 2G (900 MHz) bands overlapping. Outdated systems were quickly shut down. The American IS-54 captured the former AMPS resources.

IBM Simon is considered to be the first smartphone: mobile phone, pager, fax, PDA. The software interface provided a calendar, address book, clock, calculator, notepad, email, and an option to predict the next character like T9. The touchscreen provided control of the QWERTY keyboard. The kit included a stylus. A 1.8 MB PCMCIA memory card expanded the functionality.

2G cellular connection

There has been a tendency to minimize devices. The bricks began to weigh 100-200 g. SMS messages were first appreciated by the public. The first (automatically generated) GSM text was sent on December 2, 1992, and was tested by people in 1993. The batch prepayment method soon made SMS communication a popular pastime for young people. Later, the passion spread to older generations.

The year 1998 was marked by the appearance of the mobile payment service (Coca-Cola machines, parking lots) and the release of paid media content: the provider Radioliniya (now Eliza) sold the first ringtone. Initially, news subscriptions (2000) were distributed free of charge, the service was paid for by advertising contributions from sponsors. Secure client-bank access appeared (1999, Philippines), supported by Globe and Smart operators. At the same time, the Japanese NTT DoCoMo implemented telephone Internet.

3G

The 2G generation ended with a total victory for mobile technologies. The daily lives of billions have become filled with challenges. An innovative idea designed to increase data transfer speeds was packet switching (instead of circuit switching). The developers let go of the reins to manufacturers, concentrating entirely on consumer qualities. What was done was a consequence of the introduction of a host of standards. Compatible CDMA introduced several improvements:

1. Reduced connection setup time.
2. Increased packet speed (3.1 Mbps).
3. QoS flags.
4. Simultaneous use of a time slot by several subscribers.

The first 3G WCDMA network (May 2001, commercial use starting October 1) covered Tokyo. South Korean competitors (KTF, SK Telecom) were waiting for 2002. CDMA2000 1xEV-DO technology reached the shores of the United States, and the operator Coin managed to go bankrupt. At the same time, Japan acquired a second set of honeycombs, thanks to Vodafone. Worldwide implementation of the technology followed.

3G cellular connection

At the same time, intermediate stages of systems formation appeared - 2.5; 2.75G, for example GPRS. These means provided part of the 3G requirements, leaving out others: CDMA2000-1X is theoretically capable of providing 307 kbit/s. Next comes EDGE technology, nominally corresponding to 3G. Almost maximum thresholds are unattainable due to interference.

Gradually, television and radio companies realized the possibilities of wireless digital broadcasting. The first birds to fly were Disney and RealNetworks broadcasts. Evolution introduced the world to HSDPA (High Speed ​​Downstream Packet Access), an improved version of HSPA. The standard was recognized as 3.5G, marketers happily used the abbreviation 3G+. The current version supports data download speeds of 1.8; 3.6; 7.2; 14 Mbit/s. At the end of 2007, a total of 295 million subscribers operated networks everywhere, accounting for 9% of global demand for communications services. Superprofits ($120 billion) forced phone manufacturers to immediately modernize their production pipeline: adapters, PC set-top boxes.

4G

The results of 2009 dispassionately showed: a new generational change is coming, caused by the growing demands of the public. They began to search for technologies that increase transmission speeds tenfold. The first signs are WiMAX and LTE technologies.

Generation 4G

The infection spread across Scandinavia with lightning speed, thanks to the efforts of TeliaSoner. Network switching has been permanently removed and replaced with IP addressing. ITU standardizes (March 2008) areas:

1. Gaming applications.
2. IP telephony.
3. Internet.
4. HDTV.
5. Video conferencing.
6. 3D broadcasts.

Set speeds:

1. 100 Mbit/s – mobile objects (transport).
2. 1 Gbps – typical mobile applications.

Considering the above, the belonging of communication types LTE and WiMAX to 4G is doubtful. Experts stated that it is fundamentally impossible for technologies to reach the established level. LTE-A nominally touched the milestone, failing field tests. Engineers are pinning their hopes on the WirelessMAN-Advanced being developed. The situation is the same everywhere: the engineer works, the marketer boasts. This is how the world works.

Obstacles in the development of cellular communications

Unfortunately, economic considerations have made the concept of creating complete systems with many small areas impractical. To overcome this difficulty, system operators developed the idea of ​​cell splitting. When a service area becomes crowded with users, this approach is used to divide one zone into smaller ones. In this way, urban centers can be broken down into as many areas as needed to provide an acceptable level of service in high-traffic areas, while larger, less expensive cells can be used to cover outlying rural areas.

The latest obstacle in the development of the cellular network stems from a problem that arose when a cellular subscriber moved from one cell to another during a call. Since adjacent areas do not share the same radio channels, a call must either be dropped or transferred from one radio channel to another when a user crosses the line between adjacent cells.

Because call drop is not acceptable, a handover process was created. Handover occurs when the mobile telephone network automatically transfers the call to another radio channel when the mobile device crosses neighboring cells.

During a conversation, the two parties are on the same voice channel. When a mobile device leaves the coverage area of ​​a given cell site, reception becomes poor. At this point, the cell site being used requests handover. The system switches the call to a higher frequency channel at the new site without interrupting the call or alerting the user. The call continues as long as the user is talking and the caller does not notice the handoff.

Advantages and disadvantages of a push-button telephone

Some conservative people still use the most primitive communication devices. This is convenient if you only need your phone for communication. Let's list the main pros and cons of push-button phones.

Pros:

• simple and accessible interface;
• mechanical buttons for dialing a number or message;
• the battery holds a charge for a long time;
• the devices are strong and durable;
• Older models had strong antennas for communication.

Minuses:

• limited functionality;
• there is no possibility to take good quality photos or videos;
• using the Internet is very inconvenient;
• small and dim display;
• there is no possibility to expand the functionality with additional applications;
• some models are not designed for new three-pin SIM cards;
• There is no possibility of synchronization with some modern accessories.

Only the most basic disadvantages of push-button phones are listed. From the above we can draw the following conclusion: if you are an active and modern device user, then a push-button telephone will not suit you as your main device of use. And for older people, a phone with buttons is a great option to always stay in touch.

Cellular System Components

The cellular system offers mobile and portable telephone exchanges the same service as fixed-line exchanges over conventional wire loops. It is capable of serving tens of thousands of subscribers in a large metropolis. A cellular communications system consists of the following four main components that work together to provide mobile communications services to subscribers:

1. Public Switched Telephone Network (PSTN).
2. Mobile telephone exchange (MTSO).
3. Cell site with antenna system.
4. Mobile subscriber unit (MSU).

The PSTN consists of local area networks, exchange area networks, and long-distance networks that connect telephones and other communications devices around the world.

MTSO is the central office of mobile communications. It houses the communications switching center (MSC), field control and relay stations for switching calls from cell sites to wireline central offices (PSTN).

The term "cell site" is used to refer to the physical location of radio equipment that provides coverage in a cell. The list of hardware located at a cell site includes power supplies, interface equipment, radio frequency transmitters and receivers, and antenna systems.

The mobile subscriber unit consists of a control unit and a transceiver that transmits and receives radio transmissions to and from the cell site. Three types of MSU are available:

• Mobile phone (typical transmission power 4.0 W).
• Portable (typical transmit power 0.6 W).
• Transportable (typical transmission power is 1.6 W).

SIM cards are designed to identify subscribers

Several decades ago there were no SIM cards. Back then, to identify mobile phones on the cellular network, operators used only the ESN numbers assigned to them at the factory. At first it even seemed that this was a 100% correct decision, but in practice everything was different. When a subscriber changed a phone, he had to go to the operator’s office to register it. This one was expensive and worth the money.

A visual history of the evolution of SIM cards. Source: honeywellaidc.com

Something was needed that could separate the subscriber from his equipment. This is how Subscriber Identity Modules or SIM cards appeared in 1991. They first appeared with the advent of 2G. They were full-fledged computers with processors, permanent and RAM memory and an encryption module. The first ones were the size of a business card, but quickly decreased in size, and soon they will become built-in and rewritable - we are already on the verge of this.

The mobile phone only has an IMEI (International Mobile Equipment Identity) number. Yes, he participates in the operation of the system on the side of the cellular operator, but is not tied to the subscriber in any way. This scheme has been working properly for almost 30 years.

Each SIM card stores an ICCID serial number and PIN and PUK codes, keys, identifiers, and so on. The most important thing is the international subscriber number IMSI and a unique user identification key called KI. When a mobile device registers in the operator’s network, it uses IMSI and KI. When a SIM card is installed in a phone, smartphone or other gadget, it essentially becomes part of the phone and a link with the service provider - we have already talked about this.

Maliciousness of cell towers

Cellular communications is a major breakthrough in the science and technology of its time, which was not without consequences. The cell phone industry continues to claim that cell towers pose no health risks, but fewer people believe this these days.

Are cell towers harmful? Unfortunately, the correct answer is yes. Microwaves can affect your body's electromagnetic fields, causing a variety of potential health problems:

1. Headache.
2. Memory loss.
3. Cardiovascular stress.
4. Low sperm count.
5. Birth defects.
6. Cancer.

There is compelling evidence that electromagnetic radiation from towers is harmful to health.

Example: A study on the effects of a cage tower on a dairy herd was carried out by the government of the state of Bavaria in Germany, the results were published in 1998. The construction of the tower caused adverse health effects, leading to a noticeable drop in milk production. The movement of cattle restored milk production. Moving them back to their original pasture recreated the problem.

Advantages and disadvantages of a smartphone

The most common phones at the moment. A smartphone is a phone that has an operating system that allows you to install various software on it. Here are 5 pros and 5 cons of phones with an operating system.

Pros:

1. It is possible to install applications from any area of ​​interest.
2. The device has a built-in camera, which is usually of fairly good quality. This function allows you to use your smartphone as a full-fledged camera, video camera or video recorder.
3. A smartphone can replace a game console. On devices with good characteristics, you can play even the most modern games.
4. Big screen.
5. Touch control. The displays respond to several simultaneous clicks, which allows you to zoom in or out the picture, and also allows for comfortable control in games.

Minuses:

1. Electromagnetic radiation.
2. Formation of addiction to social networks or games.
3. Live communication is fading away.
4. The network does not catch everywhere.
5. Weak batteries.

Undoubtedly, the smartphone provides us with limitless possibilities in the field of communications. The most important thing is to skillfully use this functionality.

Cellular communications in Russia

Of the 100 possible Russian cellular codes, 79 are in use and 21 are free. Free codes are in reserve and do not yet belong to any operator.

More than 80 cellular communication companies are registered in the Russian Federation and provide their services throughout the country. Mobile operators have telephone codes in 9xx format. Mobile phone numbers are ten-digit and start with +79xx or 89xx.

The largest operators include: MTS (Mobile TeleSystems), Beeline (Vympel-Communications), MegaFon, Tele2 (T2-Mobile). The Big Three operators (MTS, Beeline and MegaFon) own entire series of numbers.

The danger from base stations is greatly exaggerated

There are a lot of myths circulating online about the dangers of mobile communications. After the installation of another cell tower, messages appear every now and then about piles of dead cockroaches, headaches and even widespread cancer.

Cell towers transmit a signal to mobile devices that falls somewhere in the spectrum between FM radio waves and microwaves. It produces non-ionizing radiation that does not affect the cellular structure. There is also ionizing radiation in nature, caused by x-rays and ultraviolet radiation. It can already change the cellular structure, so in large quantities it becomes the cause of cancer - base stations have nothing to do with it.

Base station in the city. Source: mobilecart.ru

The radiation from base stations is controlled by the energy flux density that passes through our body. On the territory of our country, it is monitored according to the standards of “Electromagnetic radiation of the radio frequency range (EMR RF)” - SanPiN 2.2.4/2.1.8.055 96. If we take into account the frequency range of base stations, in Russia there is a limit of 1 mW/m² - this is a hundred times less than in Europe and the USA. Therefore, we care much more about the health of our citizens.

As practical studies in real conditions show, the actual radiation from base stations is up to 15 times less than the limit value already at a distance of hundreds of meters - this is if the cell tower antenna is looking directly at you.

As it turns out, only cell towers located in vacant lots can be harmful to health. You are usually not allowed to enter their territory - it is fenced off with a special fence. When repair work occurs on them, all antennas are turned off and only then employees are allowed in. If you see such an object in an open field, it is better not to approach it for a long time. Having a picnic near it is not the best idea, and it is better to choose some safer place.

Large base station in a field. Source: newsko.ru

Compact femtocells are also considered dangerous. These are mini base stations that are installed in offices to improve cellular network signal reception. It is best to be at a distance of more than one or a couple meters from them.