cellular network
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A cellular network or mobile network is a
communication network A telecommunications network is a group of nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathema ...
where the link to and from end nodes is
wireless Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points that do not use an electrical conductor as a medium by which to perform the transfer. The most common wireless technolo ...

wireless
. The network is distributed over land areas called "cells", each served by at least one fixed-location
transceiver In Radio, radio communication, a transceiver is a device that is able to both transmit and receive information through a transmission medium. It is a combination of a transmitter, ''trans''mitter and a Radio receiver, re''ceiver'', hence the name ' ...

transceiver
(typically three
cell site A cell site, cell tower, or cellular base station is a cellular-enabled mobile device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical o ...
s or
base transceiver station A base transceiver station (BTS) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, ...
s). These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell. When joined together, these cells provide radio coverage over a wide geographic area. This enables numerous portable transceivers (e.g.,
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone A telephone is a telecommunications Appliance (disambiguation), devic ...

mobile phone
s, tablets and
laptop A laptop or laptop computer is a small, portable personal computer File:Crystal Project computer.png, upright=0.9, An artist's depiction of a 2000s-era desktop-style personal computer, which includes a metal case with the computing compone ...

laptop
s equipped with
mobile broadband modem A mobile broadband modem is a type of modem that allows a personal computer or a router to receive Internet access Internet access is the ability of individuals and organizations to connect to the Internet using computer terminals, computers, a ...
s,
pager A pager (also known as a beeper, bleeper or pocket bell) is a wireless telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of ...

pager
s, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission. Cellular networks offer a number of desirable features: * More capacity than a single large transmitter, since the same frequency can be used for multiple links as long as they are in different cells * Mobile devices use less power than with a single transmitter or satellite since the cell towers are closer * Larger coverage area than a single terrestrial transmitter, since additional cell towers can be added indefinitely and are not limited by the horizon Major telecommunications providers have deployed voice and data cellular networks over most of the inhabited land area of
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...
. This allows mobile phones and
mobile computing Mobile computing is human–computer interaction Human–computer interaction (HCI) studies the design and use of computer technology, focused on the interfaces between people ( users) and computer A computer is a machine that can be pr ...
devices to be connected to the public switched telephone network and public
Internet access Internet access is the ability of individuals and organizations to connect to the Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protoco ...
. Private cellular networks can be used for research or for large organizations and fleets, such as dispatch for local public safety agencies or a taxicab company.


Concept

In a
cellular radio A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone A telephone is a telecommunications Appliance (disambiguation), devic ...
system, a land area to be supplied with radio service is divided into cells in a pattern dependent on terrain and reception characteristics. These cell patterns roughly take the form of regular shapes, such as hexagons, squares, or circles although hexagonal cells are conventional. Each of these cells is assigned with multiple frequencies (''f''1 – ''f''6) which have corresponding
radio base station Base station (or base radio station) is – according to the International Telecommunication Union's (ITU) ITU Radio Regulations, Radio Regulations (RR) – a "land station in the land mobile service." The term is used in the context of mobile tel ...
s. The group of frequencies can be reused in other cells, provided that the same frequencies are not reused in adjacent cells, which would cause
co-channel interference Co-channel interference or CCI is crosstalk In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices ...
. The increased
capacity Capacity or capacities may refer to: Mathematics, science, and engineering * Capacity of a container, closely related to Volume#Related terms, the volume of the container * Capacity of a set, in Euclidean space, the total charge a set can hold whi ...
in a cellular network, compared with a network with a single transmitter, comes from the mobile communication switching system developed by Amos Joel of Bell Labs that permitted multiple callers in a given area to use the same frequency by switching calls to the nearest available cellular tower having that frequency available. This strategy is viable because a given radio frequency can be reused in a different area for an unrelated transmission. In contrast, a single transmitter can only handle one transmission for a given frequency. Inevitably, there is some level of
interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extran ...
from the signal from the other cells which use the same frequency. Consequently, there must be at least one cell gap between cells which reuse the same frequency in a standard
frequency-division multiple access Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividi ...
(FDMA) system. Consider the case of a taxi company, where each radio has a manually operated channel selector knob to tune to different frequencies. As drivers move around, they change from channel to channel. The drivers are aware of which
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. Frequency is measured in Hertz (unit), hertz ( ...

frequency
approximately covers some area. When they do not receive a signal from the transmitter, they try other channels until finding one that works. The taxi drivers only speak one at a time when invited by the base station operator. This is a form of
time-division multiple access thumbnail, 350px, TDMA frame structure showing a data stream divided into frames and those frames divided into time slots Time-division multiple access (TDMA) is a channel access method In telecommunications and computer networks, a channel ac ...
(TDMA).


History

The first commercial cellular network, the 1G generation, was launched in Japan by
Nippon Telegraph and Telephone , commonly known as NTT, is a Japanese telecommunications company headquartered in Tokyo Tokyo ( , ; Japanese language, Japanese: 東京, ''Tōkyō'' ), officially the Tokyo Metropolis (Japanese language, Japanese: 東京都, ''Tōkyō-to ...
(NTT) in 1979, initially in the metropolitan area of
Tokyo Tokyo (Japanese language, Japanese: , ''Tōkyō'' ), historically known in the west as Tokio and officially the Tokyo Metropolis (, ''Tōkyō-to''), is capital of Japan, the capital and most populous Prefectures of Japan, prefecture of Japan. ...

Tokyo
. Within five years, the NTT network had been expanded to cover the whole population of Japan and became the first nationwide 1G network. It was an analog
wireless network A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing ca ...

wireless network
. The
Bell System The Bell System was the system of companies, led by the Bell Telephone Company and later by AT&T AT&T Inc. is an American multinational conglomerate holding company, Delaware-registered but it is headquartered at Whitacre Tower in ...
had developed cellular technology since 1947, and had cellular networks in operation in
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive maps of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subd ...

Chicago
and
Dallas Dallas (), colloquially referred to as Big D, is a city in the U.S. state of Texas and the largest city in and County seat, seat of Dallas County, Texas, Dallas County, with portions extending into Collin County, Texas, Collin, Denton County, T ...
prior to 1979, but commercial service was delayed by the
breakup of the Bell System The breakup of the Bell System was mandated on January 8, 1982, by an agreed consent decree providing that AT&T Corporation would, as had been initially proposed by AT&T, relinquish control of the Bell System#History, Bell Operating Companies that ...
, with cellular assets transferred to the
Regional Bell Operating Companies The Regional Bell Operating Companies (RBOC) are the result of '' United States v. AT&T'', the U.S. Department of Justice antitrust Competition law is a law that promotes or seeks to maintain market competition by regulating anti-competiti ...
. The
wireless revolution Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points that do not use an electrical conductor In physics Physics (from grc, φυσική (ἐπιστήμη), ph ...
began in the early 1990s, leading to the transition from analog to
digital networks Digital electronics is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them. This is in contrast to analog electronics and analog signals. Digital electronic circuits are usually m ...
. This was enabled by advances in
MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS transistor, or MOS), is a type of insulated-gate field-effect transistor The field-effect trans ...

MOSFET
technology. The MOSFET, originally invented by and
Dawon Kahng Dawon Kahng ( ko, 강대원; May 4, 1931 – May 13, 1992) was a Korean-American electrical engineer and inventor, known for his work in solid-state electronics. He is best known for inventing the MOSFET (metal–oxide–semiconductor field-effect ...

Dawon Kahng
at
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial Research and development, research and scientific development S.A. ...
in 1959, was adapted for cellular networks by the early 1990s, with the wide adoption of
power MOSFET A power MOSFET is a specific type of metal–oxide–semiconductor field-effect transistor (MOSFET) designed to handle significant power levels. Compared to the other power semiconductor devices, such as an insulated-gate bipolar transistor (I ...
,
LDMOS LDMOS (laterally-diffused metal-oxide semiconductor) is a planar double-diffused MOSFET (metal–oxide–semiconductor field-effect transistor) used in amplifiers, including microwave power amplifiers, RF power amplifiers and audio power ampli ...
( RF amplifier), and RF CMOS (
RF circuit Radio-frequency (RF) engineering is a subset of electronic engineering Printed circuit board Electronic engineering (also called electronics and communications engineering) is an electrical engineering discipline which utilizes nonlinear and ...
) devices leading to the development and proliferation of digital wireless mobile networks. The first commercial digital cellular network, the 2G generation, was launched in 1991. This sparked competition in the sector as the new operators challenged the incumbent 1G analog network operators.


Cell signal encoding

To distinguish signals from several different transmitters,
frequency-division multiple access Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividi ...
(FDMA, used by analog and D-AMPS systems),
time-division multiple access thumbnail, 350px, TDMA frame structure showing a data stream divided into frames and those frames divided into time slots Time-division multiple access (TDMA) is a channel access method In telecommunications and computer networks, a channel ac ...
(TDMA, used by
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
) and
code-division multiple access Code-division multiple access (CDMA) is a channel access method used by various radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 ...
(CDMA, first used for PCS, and the basis of 3G) were developed. With FDMA, the transmitting and receiving frequencies used by different users in each cell are different from each other. Each cellular call was assigned a pair of frequencies (one for base to mobile, the other for mobile to base) to provide
full-duplex A duplex communication system 400px, Communication system A communications system or communication system is a collection of individual telecommunications network A telecommunications network is a group of nodes interconnected by links ...
operation. The original AMPS systems had 666 channel pairs, 333 each for the
CLECA competitive local exchange carrier (CLEC), in the United States and Canada, is a telecommunications provider company (sometimes called a "common carrier, carrier") competing with other, already established carriers, generally the incumbent local e ...
"A" system and
ILEC An incumbent local exchange carrier (ILEC) is a local telephone A telephone is a telecommunications Appliance (disambiguation), device that permits two or more users to conduct a conversation when they are too far apart to be heard direct ...
"B" system. The number of channels was expanded to 416 pairs per carrier, but ultimately the number of RF channels limits the number of calls that a cell site could handle. Note that FDMA is a familiar technology to telephone companies, that used
frequency-division multiplexing In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separat ...
to add channels to their point-to-point wireline plants before
time-division multiplexing Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fractio ...
rendered FDM obsolete. With TDMA, the transmitting and receiving time slots used by different users in each cell are different from each other. TDMA typically uses
digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electronics is a field of electronics Electronics comprises the physics, engineering, technology a ...
signaling to
store and forward Store and forward is a telecommunications Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essen ...
bursts of voice data that are fit into time slices for transmission, and expanded at the receiving end to produce a somewhat normal-sounding voice at the receiver. TDMA must introduce
latency Latency or latent may refer to: Science and technology * Latent heat, energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process * Latent variable, a variable that is not directly observed but inferred i ...
(time delay) into the audio signal. As long as the latency time is short enough that the delayed audio is not heard as an echo, it is not problematic. Note that TDMA is a familiar technology for telephone companies, that used
time-division multiplexing Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fractio ...
to add channels to their point-to-point wireline plants before
packet switching In telecommunications, packet switching is a method of grouping Data (computing), data that is transmitted over a digital Telecommunications network, network into ''network packet, packets''. Packets are made of a header (computing), header and a p ...
rendered FDM obsolete. The principle of CDMA is based on
spread spectrum In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (electrical engineering), signal (e.g., an electrical, electromagnetic, or acoustic signal) generated with a particular Bandwidth (signal pr ...
technology developed for military use during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all the great ...
and improved during the
Cold War The Cold War was a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc, which began following World War II. Historians do not fully agree on its sta ...
into
direct-sequence spread spectrum In telecommunications, direct-sequence spread spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference. The direct-sequence modulation makes the transmitted signal wider in bandwidth than ...
that was used for early CDMA cellular systems and
Wi-Fi Wi-Fi () is a family of wireless network Communication protocol, protocols, based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, local area networking of devices and Internet access, allowing nearby digital de ...

Wi-Fi
. DSSS allows multiple simultaneous phone conversations to take place on a single wideband RF channel, without needing to channelize them in time or frequency. Although more sophisticated than older multiple access schemes (and unfamiliar to legacy telephone companies because it was not developed by
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial Research and development, research and scientific development S.A. ...
), CDMA has scaled well to become the basis for 3G cellular radio systems. Other available methods of multiplexing such as
MIMO In radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an elec ...
, a more sophisticated version of
antenna diversity Antenna diversity, also known as space diversity or spatial diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoo ...
, combined with active
beamforming Beamforming or spatial filtering is a signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image processing, images, and ...
provides much greater
spatial multiplexing Image:spatial multiplexing2.jpg, 2xSMX or STC+2xMRC Spatial multiplexing or space-division multiplexing (often abbreviated SM, SDM or SMX) is a multiplexing technique in Multiple-input multiple-output communications, MIMO wireless communication, ...

spatial multiplexing
ability compared to original AMPS cells, that typically only addressed one to three unique spaces. Massive MIMO deployment allows much greater channel re-use, thus increasing the number of subscribers per cell site, greater data throughput per user, or some combination thereof.
Quadrature Amplitude Modulation Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications Telecommunication is the transmission of information ...
(QAM) modems offer an increasing number of bits per symbol, allowing more users per megahertz of bandwidth (and decibels of SNR), greater data throughput per user, or some combination thereof.


Frequency reuse

The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity. As described above, adjacent cells must use different frequencies, however, there is no problem with two cells sufficiently far apart operating on the same frequency, provided the masts and cellular network users' equipment do not transmit with too much power. The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, ''D'' is calculated as :D=R\sqrt, where ''R'' is the cell radius and ''N'' is the number of cells per cluster. Cells may vary in radius from . The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells. The frequency reuse factor is the rate at which the same frequency can be used in the network. It is ''1/K'' (or ''K'' according to some books) where ''K'' is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation). In case of ''N'' sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. ''N'' is typically 3. A reuse pattern of ''N/K'' denotes a further division in frequency among ''N'' sector antennas per site. Some current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 (
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
). If the total available
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thro ...
is ''B'', each cell can only use a number of frequency channels corresponding to a bandwidth of ''B/K'', and each sector can use a bandwidth of ''B/NK''.
Code-division multiple access Code-division multiple access (CDMA) is a channel access method used by various radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 ...
-based systems use a wider frequency band to achieve the same rate of transmission as FDMA, but this is compensated for by the ability to use a frequency reuse factor of 1, for example using a reuse pattern of 1/1. In other words, adjacent base station sites use the same frequencies, and the different base stations and users are separated by codes rather than frequencies. While ''N'' is shown as 1 in this example, that does not mean the CDMA cell has only one sector, but rather that the entire cell bandwidth is also available to each sector individually. Recently also
orthogonal frequency-division multiple access Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) Modulation#Digital modulation methods, digital modulation scheme. Multiple access is achieved in OFDMA ...
based systems such as LTE are being deployed with a frequency reuse of 1. Since such systems do not spread the signal across the frequency band, inter-cell radio resource management is important to coordinate resource allocation between different cell sites and to limit the inter-cell interference. There are various means of inter-cell interference coordination (ICIC) already defined in the standard. Coordinated scheduling, multi-site MIMO or multi-site beamforming are other examples for inter-cell radio resource management that might be standardized in the future.


Directional antennas

Cell towers frequently use a directional signal to improve reception in higher-traffic areas. In the
United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal di ...

United States
, the
Federal Communications Commission The Federal Communications Commission (FCC) is an Independent agencies of the United States government, independent agency of the United States government that regulates communications by radio, television, wire, satellite, and cable across the ...
(FCC) limits omnidirectional cell tower signals to 100 watts of power. If the tower has directional antennas, the FCC allows the cell operator to emit up to 500 watts of
effective radiated power#REDIRECT Effective radiated power {{Redirect category shell, 1= {{R from other capitalisation ...
(ERP). Although the original cell towers created an even, omnidirectional signal, were at the centers of the cells and were omnidirectional, a cellular map can be redrawn with the cellular telephone towers located at the corners of the hexagons where three cells converge. Each tower has three sets of directional antennas aimed in three different directions with 120 degrees for each cell (totaling 360 degrees) and receiving/transmitting into three different cells at different frequencies. This provides a minimum of three channels, and three towers for each cell and greatly increases the chances of receiving a usable signal from at least one direction. The numbers in the illustration are channel numbers, which repeat every 3 cells. Large cells can be subdivided into smaller cells for high volume areas. Cell phone companies also use this directional signal to improve reception along highways and inside buildings like stadiums and arenas.


Broadcast messages and paging

Practically every cellular system has some kind of broadcast mechanism. This can be used directly for distributing information to multiple mobiles. Commonly, for example in
mobile telephony Mobile telephony is the provision of telephone services to phones which may move around freely rather than stay fixed in one location. Telephony is supposed to specifically point to a voice-only service or connection, though sometimes the li ...
systems, the most important use of broadcast information is to set up channels for one-to-one communication between the mobile transceiver and the base station. This is called paging. The three different paging procedures generally adopted are sequential, parallel and selective paging. The details of the process of paging vary somewhat from network to network, but normally we know a limited number of cells where the phone is located (this group of cells is called a Location Area in the
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
or
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Edu ...

UMTS
system, or Routing Area if a data packet session is involved; in LTE, cells are grouped into Tracking Areas). Paging takes place by sending the broadcast message to all of those cells. Paging messages can be used for information transfer. This happens in
pagers A pager (also known as a beeper, bleeper or pocket bell) is a wireless telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of ...
, in
CDMA Code-division multiple access (CDMA) is a channel access method In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminal (telecommunication), terminals connected to the same tr ...
systems for sending
SMS SMS (short message service) is a text messaging Text messaging, or texting, is the act of composing and sending electronic messages, typically consisting of alphabetic and numeric characters, between two or more users of mobile devices, des ...
messages, and in the
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Edu ...

UMTS
system where it allows for low downlink latency in packet-based connections.


Movement from cell to cell and handing over

In a primitive taxi system, when the taxi moved away from a first tower and closer to a second tower, the taxi driver manually switched from one frequency to another as needed. If communication was interrupted due to a loss of a signal, the taxi driver asked the base station operator to repeat the message on a different frequency. In a cellular system, as the distributed mobile transceivers move from cell to cell during an ongoing continuous communication, switching from one cell frequency to a different cell frequency is done electronically without interruption and without a base station operator or manual switching. This is called the
handover In cellular telecommunications, handover, or handoff, is the process of transferring an ongoing call or data session from one channel connected to the core network to another channel. In satellite communications it is the process of transf ...
or handoff. Typically, a new channel is automatically selected for the mobile unit on the new base station which will serve it. The mobile unit then automatically switches from the current channel to the new channel and communication continues. The exact details of the mobile system's move from one base station to the other vary considerably from system to system (see the example below for how a mobile phone network manages handover).


Mobile phone network

The most common example of a cellular network is a mobile phone (cell phone) network. A
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone A telephone is a telecommunications Appliance (disambiguation), devic ...

mobile phone
is a portable telephone which receives or makes calls through a
cell site A cell site, cell tower, or cellular base station is a cellular-enabled mobile device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical o ...
(base station) or transmitting tower.
Radio wave Radio waves are a type of electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies ma ...
s are used to transfer signals to and from the cell phone. Modern mobile phone networks use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets change frequency under computer control and use low power transmitters so that the usually limited number of radio frequencies can be simultaneously used by many callers with less interference. A cellular network is used by the
mobile phone operator A mobile phone operator, wireless provider, or carrier is a mobile telecommunications company A company, abbreviated as co., is a Legal personality, legal entity representing an association of people, whether Natural person, natural, Legal per ...
to achieve both coverage and capacity for their subscribers. Large geographic areas are split into smaller cells to avoid line-of-sight signal loss and to support a large number of active phones in that area. All of the cell sites are connected to
telephone exchange manually connecting calls with cord pairs at a telephone switchboard A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It intercon ...
s (or switches), which in turn connect to the public telephone network. In cities, each cell site may have a range of up to approximately , while in rural areas, the range could be as much as . It is possible that in clear open areas, a user may receive signals from a cell site away. Since almost all mobile phones use cellular technology, including
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
,
CDMA Code-division multiple access (CDMA) is a channel access method In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminal (telecommunication), terminals connected to the same tr ...
, and AMPS (analog), the term "cell phone" is in some regions, notably the US, used interchangeably with "mobile phone". However,
satellite phone ) in use in Nias, Indonesia in April 2005 after the 2005 Nias–Simeulue earthquake, Nias–Simeulue earthquake A satellite telephone, satellite phone or satphone is a type of mobile phone that connects to other phones or the Public switched tel ...

satellite phone
s are mobile phones that do not communicate directly with a ground-based cellular tower but may do so indirectly by way of a satellite. There are a number of different digital cellular technologies, including:
Global System for Mobile Communications The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute ETSI (European Telecommunications Standards Institute) is an independent, not-for-profit, standardization Stan ...
(GSM),
General Packet Radio Service General Packet Radio Service (GPRS) is a packet oriented Statistical multiplexing is a type of communication link sharing, very similar to dynamic bandwidth allocation (DBA). In statistical multiplexing, a communication channel is divided into a ...
(GPRS),
cdmaOne Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology. It was developed by Qualcomm Qualcomm is an American multinational corporation headquartered in San Diego, California, and Delaware General Corporation ...
,
CDMA2000 CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling In signal processing Signal processing is an electrical engineering subfield that focu ...
,
Evolution-Data Optimized Evolution-Data Optimized (EV-DO, EVDO, etc.) is a telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and ...
(EV-DO), Enhanced Data Rates for GSM Evolution (EDGE),
Universal Mobile Telecommunications System The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Int ...
(UMTS),
Digital Enhanced Cordless Telecommunications#REDIRECT Digital enhanced cordless telecommunications {{Redirect category shell, {{R from move ...
(DECT),
Digital AMPS IS-54 and IS-136 are second-generation ( 2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System Advanced Mobile Phone System (AMPS) was an analog ...
(IS-136/TDMA), and
Integrated Digital Enhanced Network Integrated Digital Enhanced Network (iDEN) is a mobile telecommunications technology, developed by Motorola, which provides its users the benefits of a trunked radio and a cellular telephone A mobile phone, cellular phone, cell phone, ce ...
(iDEN). The transition from existing analog to the digital standard followed a very different path in Europe and the . As a consequence, multiple digital standards surfaced in the US, while
Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest ...

Europe
and many countries converged towards the
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
standard.


Structure of the mobile phone cellular network

A simple view of the cellular mobile-radio network consists of the following: * A network of radio
base station Base station (or base radio station) is – according to the International Telecommunication Union File:ITU monument, Bern.jpg, 260px, ITU Monument, Bern The International Telecommunication Union is a list of specialized agencies of the Uni ...
s forming the
base station subsystem The base station subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, o ...
. * The core circuit switched network for handling voice calls and text * A
packet switched network In telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of ...
for handling mobile data * The public switched telephone network to connect subscribers to the wider telephony network This network is the foundation of the
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
system network. There are many functions that are performed by this network in order to make sure customers get the desired service including mobility management, registration, call set-up, and
handover In cellular telecommunications, handover, or handoff, is the process of transferring an ongoing call or data session from one channel connected to the core network to another channel. In satellite communications it is the process of transf ...
. Any phone connects to the network via an RBS (
Radio Base Station Base station (or base radio station) is – according to the International Telecommunication Union's (ITU) ITU Radio Regulations, Radio Regulations (RR) – a "land station in the land mobile service." The term is used in the context of mobile tel ...
) at a corner of the corresponding cell which in turn connects to the
Mobile switching center Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management Mobility management is one of the major functions of a GSM or a UMTS The Universal Mobile Telecommuni ...
(MSC). The MSC provides a connection to the public switched telephone network (PSTN). The link from a phone to the RBS is called an ''uplink'' while the other way is termed ''downlink''. Radio channels effectively use the transmission medium through the use of the following multiplexing and access schemes:
frequency-division multiple access Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividi ...
(FDMA),
time-division multiple access thumbnail, 350px, TDMA frame structure showing a data stream divided into frames and those frames divided into time slots Time-division multiple access (TDMA) is a channel access method In telecommunications and computer networks, a channel ac ...
(TDMA),
code-division multiple access Code-division multiple access (CDMA) is a channel access method used by various radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 ...
(CDMA), and
space-division multiple access Space-division multiple access (SDMA) is a channel access method In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminal (telecommunication), terminals connected to the same tr ...
(SDMA).


Small cells

Small cells, which have a smaller coverage area than base stations, are categorised as follows: *
Microcell A microcell is a cell in a mobile phone network served by a low power cellular base station (tower), covering a limited area such as a mall, a hotel, or a transportation hub. A microcell is usually larger than a picocell, though the distinction ...
-> less than 2 kilometres, *
Picocell A picocell is a small cellular base station typically covering a small area, such as in-building (offices, shopping malls, train stations, stock exchanges, etc.), or more recently in-aircraft. In cellular networks, picocells are typically used to ex ...
-> less than 200 metres, *
Femtocell In telecommunications Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of ...
-> around 10 metres, * Attocell -> 1–4 metres


Cellular handover in mobile phone networks

As the phone user moves from one cell area to another cell while a call is in progress, the mobile station will search for a new channel to attach to in order not to drop the call. Once a new channel is found, the network will command the mobile unit to switch to the new channel and at the same time switch the call onto the new channel. With
CDMA Code-division multiple access (CDMA) is a channel access method In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminal (telecommunication), terminals connected to the same tr ...
, multiple CDMA handsets share a specific radio channel. The signals are separated by using a pseudonoise code (PN code) that is specific to each phone. As the user moves from one cell to another, the handset sets up radio links with multiple cell sites (or sectors of the same site) simultaneously. This is known as "soft handoff" because, unlike with traditional cellular technology, there is no one defined point where the phone switches to the new cell. In
IS-95 Interim Standard 95 (IS-95) was the first ever code-division multiple access, CDMA-based digital cellular technology. It was developed by Qualcomm and later adopted as a standard by the Telecommunications Industry Association in TIA/EIA/IS-95 r ...
inter-frequency handovers and older analog systems such as NMT it will typically be impossible to test the target channel directly while communicating. In this case, other techniques have to be used such as pilot beacons in IS-95. This means that there is almost always a brief break in the communication while searching for the new channel followed by the risk of an unexpected return to the old channel. If there is no ongoing communication or the communication can be interrupted, it is possible for the mobile unit to spontaneously move from one cell to another and then notify the base station with the strongest signal.


Cellular frequency choice in mobile phone networks

The effect of frequency on cell coverage means that different frequencies serve better for different uses. Low frequencies, such as 450  MHz NMT, serve very well for countryside coverage.
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
900 (900 MHz) is suitable for light urban coverage.
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
1800 (1.8  GHz) starts to be limited by structural walls.
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Edu ...

UMTS
, at 2.1 GHz is quite similar in coverage to
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
1800. Higher frequencies are a disadvantage when it comes to coverage, but it is a decided advantage when it comes to capacity. Picocells, covering e.g. one floor of a building, become possible, and the same frequency can be used for cells which are practically neighbors. Cell service area may also vary due to interference from transmitting systems, both within and around that cell. This is true especially in CDMA based systems. The receiver requires a certain
signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and b ...
, and the transmitter should not send with too high transmission power in view to not cause interference with other transmitters. As the receiver moves away from the transmitter, the power received decreases, so the power control algorithm of the transmitter increases the power it transmits to restore the level of received power. As the interference (noise) rises above the received power from the transmitter, and the power of the transmitter cannot be increased anymore, the signal becomes corrupted and eventually unusable. In CDMA-based systems, the effect of interference from other mobile transmitters in the same cell on coverage area is very marked and has a special name, '' cell breathing''. One can see examples of cell coverage by studying some of the coverage maps provided by real operators on their web sites or by looking at independently crowdsourced maps such as Opensignal or CellMapper. In certain cases they may mark the site of the transmitter; in others, it can be calculated by working out the point of strongest coverage. A cellular repeater is used to extend cell coverage into larger areas. They range from wideband repeaters for consumer use in homes and offices to smart or digital repeaters for industrial needs.


Cell size

The following table shows the dependency of the coverage area of one cell on the frequency of a
CDMA2000 CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling In signal processing Signal processing is an electrical engineering subfield that focu ...
network:


See also

Lists and technical information: * Mobile technology, Mobile technologies ** 2G networks (the first digital networks, 1G and Mobile radio telephone, 0G were analog): ***
GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music and Drama i ...

GSM
****Circuit Switched Data (CSD) **** GPRS **** EDGE(IMT-SC) **** Evolved EDGE ***
Digital AMPS IS-54 and IS-136 are second-generation ( 2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System Advanced Mobile Phone System (AMPS) was an analog ...
****Cellular Digital Packet Data (CDPD) ***
cdmaOne Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology. It was developed by Qualcomm Qualcomm is an American multinational corporation headquartered in San Diego, California, and Delaware General Corporation ...
(IS-95) ****Circuit Switched Data (CSD) ** 3G networks: *** Universal Mobile Telecommunications System, UMTS **** W-CDMA (air interface) **** TD-CDMA (air interface) **** TD-SCDMA (air interface) ***** High Speed Packet Access, HSPA ***** HSDPA ***** HSPA+ ***
CDMA2000 CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling In signal processing Signal processing is an electrical engineering subfield that focu ...
**** OFDMA (air interface) ***** EVDO ****** SVDO ** 4G networks: *** LTE (telecommunication), LTE (TD-LTE) **** LTE Advanced **** LTE Advanced Pro *** WiMAX **** WiMAX-Advanced (WirelessMAN-Advanced) *** Ultra Mobile Broadband (never commercialized) *** IEEE 802.20, MBWA (IEEE 802.20, Mobile Broadband Wireless Access, HC-SDMA, iBurst, has been shut down) ** 5G networks: *** 5G NR ***5G-Advanced Starting with EVDO the following techniques can also be used to improve performance: *
MIMO In radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an elec ...
, Space-division multiple access, SDMA and Beamforming * Cellular frequencies ** GSM frequency bands ** UMTS frequency bands ** LTE frequency bands ** 5G NR frequency bands * Deployed networks by technology ** List of UMTS networks ** List of CDMA2000 networks ** List of LTE networks ** List of deployed WiMAX networks ** List of 5G NR networks * Deployed networks by country (including technology and frequencies) ** List of mobile network operators of Europe ** List of mobile network operators of the Americas ** List of mobile network operators of the Asia Pacific region ** List of mobile network operators of the Middle East and Africa ** List of mobile network operators (summary) * Mobile country code - code, frequency, and technology for each operator in each country * Comparison of mobile phone standards Equipment: * Cellular repeater * Cellular router * Professional mobile radio (PMR) * OpenBTS Other: * IUC: Interconnected Usage Charge * Cellular traffic *
MIMO In radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an elec ...
(multiple-input and multiple-output) * Mobile edge computing * Mobile phone radiation and health * Network simulation * Radio resource management (RRM) * Routing in cellular networks * Signal strength * Title 47 of the Code of Federal Regulations


References


Further reading

* P. Key, D. Smith. Teletraffic Engineering in a competitive world. Elsevier Science B.V., Amsterdam Netherlands, 1999. . Chapter 1 (Plenary) and 3 (mobile). * William C. Y. Lee, ''Mobile Cellular Telecommunications Systems'' (1989), McGraw-Hill.


External links

*
A History of Cellular Networks

What are cellular networks? 1G to 6G Features & Evolution
{{DEFAULTSORT:Cellular Network Mobile telecommunications Radio resource management Telecommunications infrastructure Japanese inventions Wireless communication systems