Editing Cellular network

{{Short description|Communication network}}
{{About|the infrastructure of cellular networks|the companies that provide services on these networks|Mobile network operator}}
{{Use dmy dates|date=October 2017}}
[[File:CellTowerRichmondHill.jpg|thumb|Top of a cellular radio tower]]
[[File:Indoor Sendeanlage Deutsche Telekom.jpg|thumb|Indoor cell site in Germany]]
{{Antennas|systems}}

A '''cellular network''' or '''mobile network''' is a [[telecommunications network]] where the link to and from end nodes is [[wireless network|wireless]] and the network is distributed over land areas called '''''cells''''', each served by at least one fixed-location [[transceiver]] (such as a [[base station]]). These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content via [[radio wave]]s. Each cell's coverage area is determined by factors such as the power of the transceiver, the terrain, and the frequency band being used. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell.<ref>{{Cite web |title=Cellular Networks, Cells, and Base Stations — EITC |url=http://www.eitc.org/research-opportunities/5g-and-beyond-mobile-wireless-technology/5g-and-beyond-technology-roadmap/cellular-cellular-technology-and-ran/cellular-networks-base-stations-and-5g-ran/cellular-networks-1/cellular-networks-cells-and-base-stations-1/cellular-networks-cells-and-base-stations |access-date=2024-11-22 |website=www.eitc.org}}</ref><ref name=Zander>{{cite book|author1=Guowang Miao|author2=Jens Zander|author3=Ki Won Sung|author4=Ben Slimane|title=Fundamentals of Mobile Data Networks|publisher=[[Cambridge University Press]]|isbn=978-1107143210|year=2016|author1-link=Guowang Miao}}</ref>

When joined together, these cells provide radio coverage over a wide geographic area. This enables numerous [[Mobile device|devices]], including [[mobile phone]]s, [[Tablet computer|tablets]], [[laptop]]s equipped with [[mobile broadband modem]]s, and [[Wearable technology|wearable devices]] such as [[smartwatch]]es, to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the devices are moving through more than one cell during transmission. The design of cellular networks allows for seamless [[handover]], enabling uninterrupted communication when a device moves from one cell to another.

Modern cellular networks utilize advanced technologies such as [[MIMO|Multiple Input Multiple Output]] (MIMO), [[beamforming]], and small cells to enhance network capacity and efficiency.

Cellular networks offer a number of desirable features:<ref name=Zander/>
* 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 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
* Capability of utilizing higher frequency signals (and thus more available bandwidth / faster data rates) that are not able to propagate at long distances
* With data compression and multiplexing, several video (including digital video) and audio channels may travel through a higher frequency signal on a single wideband carrier
Major telecommunications providers have deployed voice and data cellular networks over most of the inhabited land area of [[Earth]]. This allows mobile phones and other devices to be connected to the [[public switched telephone network]] and public [[Internet access]]. In addition to traditional voice and data services, cellular networks now support [[Internet of things|Internet of Things]] (IoT) applications, connecting devices such as [[smart meter]]s, vehicles, and industrial sensors.

The evolution of cellular networks from [[1G]] to [[5G]] has progressively introduced faster speeds, lower latency, and support for a larger number of devices, enabling advanced applications in fields such as healthcare, transportation, and [[Smart city|smart cities]].

Private cellular networks can be used for research<ref>{{cite web |author=Tom Simonite |url=http://www.technologyreview.com/view/510341/googles-private-cell-phone-network/ |title=Google's Private Cell Phone Network Could Be a Threat to Cellular Carriers &#124; MIT Technology Review |publisher=Technologyreview.com |date=24 January 2013 |access-date=23 November 2013 |archive-date=29 October 2013 |archive-url=https://web.archive.org/web/20131029201118/http://www.technologyreview.com/view/510341/googles-private-cell-phone-network/ |url-status=live }}</ref> or for large organizations and fleets, such as dispatch for local public safety agencies or a taxicab company, as well as for local wireless communications in enterprise and industrial settings such as factories, warehouses, mines, power plants, substations, oil and gas facilities and ports.<ref>{{Cite web |title=Private 5G Networks: 2024 – 2030 |url=https://www.snstelecom.com/private5g |access-date=2024-05-08 |website=www.snstelecom.com |language=en-US}}</ref>

== Concept ==
{{More citations needed section|date=February 2025}}
[[File:frequency reuse.svg|thumb|Example of frequency reuse factor or pattern, with four frequencies (F1-F4)]]
In a [[cellular radio]] 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''<sub>1</sub>&nbsp;–&nbsp;''f''<sub>6</sub>) which have corresponding [[radio base station]]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]].

The increased [[Channel capacity|capacity]] in a cellular network, compared with a network with a single transmitter, comes from the mobile communication switching system developed by [[Amos E. Joel Jr.|Amos Joel]] of Bell Labs<ref>{{US patent|3,663,762}}, issued 16 May 1972.</ref> 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 [[co-channel interference|interference]] 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]] (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]] 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]] (TDMA).

== History ==
{{see also|History of mobile phones}}
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| image2            = E-call in a vw e-golf 2018.jpg
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| footer            = Examples of modern devices that may use cellular networks: a mobile phone (top-left), an [[Panic button|emergency/panic button]] in a car (top-right), an electricity [[smart meter]] (bottom-left) and a [[Mobile broadband modem|mobile broadband USB modem]] attached to a laptop (bottom-right)
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The idea to establish a standard cellular phone network was first proposed on December 11, 1947. This proposal was put forward by [[Douglas H. Ring]], a [[Bell Labs]] engineer, in an internal memo suggesting the development of a cellular telephone system by [[AT&T]].<ref>{{cite magazine |url=https://www.theatlantic.com/technology/archive/2011/09/the-1947-paper-that-first-described-a-cell-phone-network/245222/ |title=The 1947 Paper That First Described a Cell-Phone Network |date=September 16, 2011 |author=Alexis C. Madrigal |magazine=[[The Atlantic]]}}</ref><ref>{{Cite web |last=Zhou |first=Shengjun |date=2024-02-02 |title=From 0G to 5G, the century-long ups and downs of mobile communication |url=https://medium.com/@xzclass/from-0g-to-5g-the-century-long-ups-and-downs-of-mobile-communication-d9840e191c19 |access-date=2025-01-08 |website=Medium |language=en}}</ref>

The first commercial cellular network, the [[1G]] generation, was launched in Japan by [[Nippon Telegraph and Telephone]] (NTT) in 1979, initially in the metropolitan area of [[Tokyo]]. However, NTT did not initially commercialize the system; the early launch was motivated by an effort to understand a practical cellular system rather than by an interest to profit from it.<ref name=":1">{{Cite web |title=Cellular : an economic and business history of the international mobile-phone industry {{!}} Library of Congress |url=https://www.loc.gov/resource/gdcebookspublic.2021060544/ |access-date=2025-01-08 |website=www.loc.gov}}</ref><ref>{{Cite journal |last=Dunnewijk |first=Theo |last2=Hultén |first2=Staffan |date=2007-08-01 |title=A brief history of mobile communication in Europe |url=https://linkinghub.elsevier.com/retrieve/pii/S0736585307000226 |journal=Telematics and Informatics |series=Mobile Communications: From Cellular to Ad-hoc and Beyond |volume=24 |issue=3 |pages=164–179 |doi=10.1016/j.tele.2007.01.013 |issn=0736-5853|url-access=subscription }}</ref> In 1981, the [[Nordic Mobile Telephone]] system was created as the first network to cover an entire country. The network was released in 1981 in Sweden and Norway, then in early 1982 in Finland and Denmark. [[Televerket (Sweden)|Televerket]], a state-owned corporation responsible for telecommunications in Sweden, launched the system.<ref name=":1" /><ref>{{Cite journal |last=Al-Khouri |first=Ali M. |date=2015 |title=Towards a SIM-less Existence: The Evolution of Smart Learning Networks |url=http://www.jstor.org/stable/44430335 |journal=Educational Technology |volume=55 |issue=1 |pages=19–26 |issn=0013-1962}}</ref><ref>{{Cite news |last=Carlsson |first=Lennart |last2=Tribune |first2=International Herald |date=1991-10-08 |title=Nordic Mobile Phones a Ringing Success |url=https://www.nytimes.com/1991/10/08/IHT-nordic-mobile-phones-a-ringing-success.html |access-date=2025-01-08 |work=The New York Times |language=en-US |issn=0362-4331}}</ref>

In September 1981, [[Jan Stenbeck#:~:text=He was head of Kinnevik,people, worth some $800 million.|Jan Stenbeck]], a financier and businessman, launched [[Comviq#:~:text=The original Comvik was established,launch of its NMT network.|Comvik]], a new Swedish telecommunications company. Comvik was the first European telecommunications firm to challenge the state's telephone monopoly on the industry.<ref>{{Citation |last=Syvertsen |first=Trine |title=The Nordic Media Company |date=2014 |work=The Media Welfare State |pages=96–118 |url=http://www.jstor.org/stable/j.ctv65swsg.8 |access-date=2025-01-09 |series=Nordic Media in the Digital Era |publisher=University of Michigan Press |doi=10.2307/j.ctv65swsg.8 |last2=Enli |first2=Gunn |last3=Mjøs |first3=Ole J. |last4=Moe |first4=Hallvard|url-access=subscription }}</ref><ref>{{Cite book |last=Garrard |first=Garry A. |title=Cellular communications: worldwide market development |date=1998 |publisher=Artech House |isbn=978-0-89006-923-3 |series=The Artech House mobile communications series |location=Boston}}</ref><ref name=":2">{{Cite journal |last=Eriksson |first=Klas |last2=Lakomaa |first2=Erik |last3=Nykvist |first3=Rasmus |last4=Sandström |first4=Christian |date=2024-03-05 |title=Introducing the inverted Icarus paradox in business history – Evidence from David and Goliath in the Swedish telecommunications industry 1981–1990 |url=https://www.tandfonline.com/doi/full/10.1080/00076791.2023.2292134 |journal=Business History |language=en |pages=1–26 |doi=10.1080/00076791.2023.2292134 |issn=0007-6791|doi-access=free }}</ref> According to some sources, Comvik was the first to launch a commercial automatic cellular system before Televerket launched its own in October 1981. However, at the time of the new network’s release, the [[Swedish Post and Telecom Authority]] threatened to shut down the system after claiming that the company had used an unlicensed automatic gear that could interfere with its own networks.<ref name=":2" /><ref name=":3">{{Cite book |last=Andersson |first=Per |title=Stenbeck: En biografi över en framgångsrik affärsman |date=2014 |publisher=Modernista |isbn=978-91-7499-230-4}}</ref> In December 1981, Sweden awarded Comvik with a license to operate its own automatic cellular network in the spirit of market competition.<ref name=":2" /><ref name=":3" /><ref>{{Cite book |last=Mölleryd |first=Bengt G. |title=Entrepreneurship in technological systems: the development of mobile telephony in Sweden |date=1999 |publisher=Economic Research Institute, Stockholm School of Economics [Ekonomiska forskningsinstitutet vid Handelshögsk.] (EFI |isbn=978-91-7258-523-2 |location=Stockholm}}</ref>

The [[Bell System]] had developed cellular technology since 1947, and had cellular networks in operation in [[Chicago]], Illinois,<ref>{{cite journal |title=Advanced Mobile Phone Service: The Developmental System |journal=[[Bell System Technical Journal]] |volume=58 |issue=1 |pages=249-269 |date=January 1979 |doi=10.1002/j.1538-7305.1979.tb02218.x}}</ref> and [[Dallas]], Texas, prior to 1979; however, regulatory battles delayed AT&T's deployment of cellular service to 1983,<ref>{{cite web |url=https://www.justice.gov/archives/atr/att-divestiture-was-it-necessary-was-it-success |title=The AT&T Divestiture: Was It Necessary? Was It a Success? |author=Robert W. Crandall |at=Slide 11 |date=March 28, 2007}}</ref> when its [[Regional Holding Company]] [[Illinois Bell]] first provided cellular service.<ref>{{cite web |url=http://www.corp.att.com/attlabs/reputation/timeline/46mobile.html |title=1946: First Mobile Telephone Call |year=2011 |website=AT&T Labs |access-date=2012-04-24 |url-status=dead |archive-url=https://web.archive.org/web/20121212113039/http://www.corp.att.com/attlabs/reputation/timeline/46mobile.html |archive-date=2012-12-12}}</ref>

First-generation cellular network technology continued to expand its reach to the rest of the world. In 1990, [[Millicom|Millicom Inc.]], a telecommunications service provider, strategically partnered with Comvik’s international cellular operations to become Millicom International Cellular SA.<ref>“[https://www.sec.gov/Archives/edgar/data/912958/000104746904010287/a2132538z6-k.htm Millicom International Cellular S.A.] (31, March 2004). Form 6-K. Retrieved from the Securities and Exchange Commission". </ref> The company went on to establish a 1G systems foothold in Ghana, Africa under the brand name Mobitel.<ref>[https://www.sec.gov/Archives/edgar/data/912958/000104746909003511/a2191853z20-f.htm “Millicom International Cellular S.A.] (31, Dec. 2008). Form 20-F. Retrieved from the Securities and Exchange Commission".</ref> In 2006, the company’s Ghana operations were renamed to Tigo.<ref>{{Cite web |title=Bharti Airtel and Millicom announce deal closure to combine operations in Ghana |url=https://www.bharti.com/press-release-2017-2018-bharti-airtel-millicom-announce.html |access-date=2025-01-10 |website=www.bharti.com}}</ref>

The [[wireless revolution]] began in the early 1990s,<ref name="Golio">{{cite book |last1=Golio |first1=Mike |last2=Golio |first2=Janet |title=RF and Microwave Passive and Active Technologies |date=2018 |publisher=[[CRC Press]] |isbn=9781420006728 |pages=ix, I-1, 18-2 |url=https://books.google.com/books?id=MCj9jxSVQKIC&pg=PR9 |access-date=16 October 2019 |archive-date=22 January 2023 |archive-url=https://web.archive.org/web/20230122155510/https://books.google.com/books?id=MCj9jxSVQKIC&pg=PR9 |url-status=live }}</ref><ref>{{cite journal |last1=Rappaport |first1=T. S. |title=The wireless revolution |journal=IEEE Communications Magazine |date=November 1991 |volume=29 |issue=11 |pages=52–71 |doi=10.1109/35.109666 |s2cid=46573735 }}</ref><ref>{{cite news |title=The wireless revolution |url=https://www.economist.com/leaders/1999/01/21/the-wireless-revolution |access-date=12 September 2019 |newspaper=[[The Economist]] |date=January 21, 1999 |archive-date=16 October 2019 |archive-url=https://web.archive.org/web/20191016153230/https://www.economist.com/leaders/1999/01/21/the-wireless-revolution |url-status=live }}</ref> leading to the transition from analog to [[digital electronics|digital networks]].<ref name="Baliga">{{cite book |last1=Baliga |first1=B. Jayant |author1-link=B. Jayant Baliga |title=Silicon RF Power MOSFETS |date=2005 |publisher=[[World Scientific]] |isbn=9789812561213 |url=https://books.google.com/books?id=StJpDQAAQBAJ |access-date=16 October 2019 |archive-date=22 January 2023 |archive-url=https://web.archive.org/web/20230122155511/https://books.google.com/books?id=StJpDQAAQBAJ |url-status=live }}</ref> The MOSFET invented at [[Bell Labs]] between 1955 and 1960,<ref name=":0">{{Cite journal |last1=Huff |first1=Howard |last2=Riordan |first2=Michael |date=2007-09-01 |title=Frosch and Derick: Fifty Years Later (Foreword) |url=https://iopscience.iop.org/article/10.1149/2.F02073IF |journal=The Electrochemical Society Interface |volume=16 |issue=3 |pages=29 |doi=10.1149/2.F02073IF |issn=1064-8208|url-access=subscription }}</ref><ref>{{Cite journal |last1=Frosch |first1=C. J. |last2=Derick |first2=L |date=1957 |title=Surface Protection and Selective Masking during Diffusion in Silicon |url=https://iopscience.iop.org/article/10.1149/1.2428650 |journal=Journal of the Electrochemical Society |language=en |volume=104 |issue=9 |pages=547 |doi=10.1149/1.2428650|url-access=subscription }}</ref><ref name="Lojek1202">{{cite book |last1=Lojek |first1=Bo |title=History of Semiconductor Engineering |date=2007 |publisher=[[Springer Science & Business Media]] |isbn=9783540342588 |page=120}}</ref><ref>{{Cite book |last=Lojek |first=Bo |title=History of Semiconductor Engineering |date=2007 |publisher=Springer-Verlag Berlin Heidelberg |isbn=978-3-540-34258-8 |location=Berlin, Heidelberg |page=321}}</ref><ref>{{Cite journal |last1=Ligenza |first1=J.R. |last2=Spitzer |first2=W.G. |date=1960 |title=The mechanisms for silicon oxidation in steam and oxygen |url=https://linkinghub.elsevier.com/retrieve/pii/0022369760902195 |journal=Journal of Physics and Chemistry of Solids |language=en |volume=14 |pages=131–136 |bibcode=1960JPCS...14..131L |doi=10.1016/0022-3697(60)90219-5|url-access=subscription }}</ref> was adapted for cellular networks by the early 1990s, with the wide adoption of [[power MOSFET]], [[LDMOS]] ([[RF amplifier]]), and [[RF CMOS]] ([[RF circuit]]) devices leading to the development and proliferation of digital wireless mobile networks.<ref name="Baliga"/><ref name="Asif">{{cite book |last1=Asif |first1=Saad |title=5G Mobile Communications: Concepts and Technologies |date=2018 |publisher=[[CRC Press]] |isbn=9780429881343 |pages=128–134 |url=https://books.google.com/books?id=yg1mDwAAQBAJ&pg=PT128 |access-date=16 October 2019 |archive-date=22 January 2023 |archive-url=https://web.archive.org/web/20230122155511/https://books.google.com/books?id=yg1mDwAAQBAJ&pg=PT128 |url-status=live }}</ref><ref name="O'Neill">{{cite journal |last1=O'Neill |first1=A. |title=Asad Abidi Recognized for Work in RF-CMOS |journal=IEEE Solid-State Circuits Society Newsletter |date=2008 |volume=13 |issue=1 |pages=57–58 |doi=10.1109/N-SSC.2008.4785694 |issn=1098-4232}}</ref>

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, a number of [[channel access method]]s have been developed, including [[frequency-division multiple access]] (FDMA, used by analog and [[D-AMPS]]{{citation needed|date=November 2019}} systems), [[time-division multiple access]] (TDMA, used by [[GSM]]) and [[code-division multiple access]] (CDMA, first used for [[Personal Communications Service|PCS]], and the basis of [[3G]]).<ref name=Zander/>

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]] operation. The original [[Advanced Mobile Phone Service|AMPS]] systems had 666 channel pairs, 333 each for the [[competitive local exchange carrier|CLEC]] "A" system and [[incumbent local exchange carrier|ILEC]] "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. FDMA is a familiar technology to telephone companies, which used [[frequency-division multiplexing]] to add channels to their point-to-point wireline plants before [[time-division multiplexing]] 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 data|digital]] signaling to [[store and forward]] 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 (audio)|latency]] (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. TDMA is a familiar technology for telephone companies, which used [[time-division multiplexing]] to add channels to their point-to-point wireline plants before [[packet switching]] rendered FDM obsolete.

The principle of CDMA is based on [[spread spectrum]] technology developed for military use during [[World War II]] and improved during the [[Cold War]] into [[direct-sequence spread spectrum]] that was used for early CDMA cellular systems and [[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]]), CDMA has scaled well to become the basis for 3G cellular radio systems.

Other available methods of multiplexing such as [[MIMO]], a more sophisticated version of [[antenna diversity]], combined with active [[beamforming]] provides much greater [[spatial multiplexing]] ability compared to original AMPS cells, that typically only addressed one to three unique spaces. Massive MIMO deployment allows much greater channel reuse, thus increasing the number of subscribers per cell site, greater data throughput per user, or some combination thereof. [[Quadrature Amplitude Modulation]] (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 reuse 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.<ref name=Zander/>

The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, ''D'' is calculated as

:<math>D=R\sqrt{3N}</math>,

where ''R'' is the cell radius and ''N'' is the number of cells per cluster. Cells may vary in radius from {{convert|1|to|30|km}}. The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells.<ref>J. E. Flood. Telecommunication Networks. Institution of Electrical Engineers, London, UK, 1997. chapter 12.</ref>

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).<ref>{{cite web|url=http://www.thereversephone.com/phone-networks/phone-networks/|title=Phone Networks|date=8 June 2011|publisher=The Reverse Phone|access-date=2 April 2012|archive-url=https://web.archive.org/web/20120430205327/http://www.thereversephone.com/phone-networks/phone-networks/|archive-date=30 April 2012|url-status=dead|df=dmy-all}}</ref>

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]]).

If the total available [[bandwidth (signal processing)|bandwidth]] 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]]-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]] based systems such as [[3GPP Long Term Evolution|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.<ref>{{cite web|url=http://www.nomor.de/uploads/a4/81/a4815c4dc585be33c81f0ec7a15deed7/2010-12-WhitePaper_LTE_HetNet_ICIC.pdf|title=Heterogeneous LTE Networks and Inter-Cell Interference Coordination|last=Pauli|first=Volker|author2=Naranjo, Juan Diego|author3=Seidel, Eiko|date=December 2010|publisher=Nomor Research|access-date=2 April 2012|archive-url=https://web.archive.org/web/20130903122150/http://www.nomor.de/uploads/a4/81/a4815c4dc585be33c81f0ec7a15deed7/2010-12-WhitePaper_LTE_HetNet_ICIC.pdf|archive-date=3 September 2013|url-status=dead|df=dmy-all}}</ref> 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 ==
[[File:CellTowersAtCorners.gif|thumb|382px|Cellular telephone frequency reuse pattern. See {{US patent|4,144,411}}]]

Cell towers frequently use a [[Directional antenna|directional signal]] to improve reception in higher-traffic areas. In the [[United States]], the [[Federal Communications Commission]] (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]] (ERP).<ref name=Drucker>{{Citation
| title = The Myth of Cellular Tower Health Hazards
| url = http://www.wirelessweek.com/news/2007/03/myth-cellular-tower-health-hazards
| author = Drucker, Elliott
| access-date = 19 November 2013
| archive-url = https://web.archive.org/web/20140502012734/http://www.wirelessweek.com/news/2007/03/myth-cellular-tower-health-hazards
| archive-date = 2 May 2014
| url-status = dead
}}</ref>

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.<ref>{{cite web|url=http://www.privateline.com/Cellbasics/Cellbasics02.html|title=Cellular Telephone Basics|date=1 January 2006|publisher=Privateline.com|page=2|access-date=2 April 2012|url-status=dead|archive-url=https://web.archive.org/web/20120417220750/http://www.privateline.com/Cellbasics/Cellbasics02.html|archive-date=17 April 2012}}</ref>  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.<ref>{{US patent|4144411}} – ''Cellular Radiotelephone System for Different Cell Sizes'' – Richard H. Frenkiel (Bell Labs), filed 22 September 1976, issued 13 March 1979</ref>

Cell phone companies also use this directional signal to improve reception along highways and inside buildings like stadiums and arenas.<ref name="Drucker"/>

== 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]] 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]] or [[UMTS]] system, or Routing Area if a data packet session is involved; in [[3GPP Long Term Evolution|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 [[paging (telecommunications)|pagers]], in [[CDMA]] systems for sending [[Short message service|SMS]] messages, and in the [[UMTS]] system where it allows for low downlink latency in packet-based connections.

In LTE/4G, the Paging procedure is initiated by the MME when data packets need to be delivered to the UE.

Paging types supported by the MME are:

* Basic.
* SGs_CS and SGs_PS.
* QCI_1 through QCI_9.

== 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]] 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 ==
[[File:GSM ArchitecturePL.svg|thumb|300px|WCDMA network architecture|alt=3G network]]
The most common example of a cellular network is a mobile phone (cell phone) network. A [[mobile phone]] is a portable telephone which receives or makes calls through a [[cell site]] (base station) or transmitting tower. [[Radio wave]]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]] 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]]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 {{convert|1/2|mi}}, while in rural areas, the range could be as much as {{convert|5|mi}}. It is possible that in clear open areas, a user may receive signals from a cell site {{convert|25|mi}} away.  In rural areas with low-band coverage and tall towers, basic voice and messaging service may reach {{convert|50|mi}}, with limitations on bandwidth and number of simultaneous calls. {{citation needed|date=August 2022}}
 
Since almost all mobile phones use [[cellular technology]], including [[GSM]], [[CDMA]], and [[Advanced Mobile Phone System|AMPS]] (analog), the term "cell phone" is in some regions, notably the US, used interchangeably with "mobile phone". However, [[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]] (GSM), [[General Packet Radio Service]] (GPRS), [[cdmaOne]], [[CDMA2000]], [[Evolution-Data Optimized]] (EV-DO), [[Enhanced Data Rates for GSM Evolution]] (EDGE), [[Universal Mobile Telecommunications System]] (UMTS), [[Digital Enhanced Cordless Telecommunications]] (DECT), [[Digital AMPS]] (IS-136/TDMA), and [[Integrated Digital Enhanced Network]] (iDEN). The transition from existing analog to the digital standard followed a very different path in Europe and the [[United States|US]].<ref>Paetsch, Michael (1993): The evolution of mobile communications in the US and Europe. Regulation, technology, and markets. Boston, London: Artech House (The Artech House mobile communications library).
</ref> As a consequence, multiple digital standards surfaced in the US, while [[Europe]] and many countries converged towards the [[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]]s forming the [[base station subsystem]].
* The [[Network switching subsystem|core circuit switched network]] for handling voice calls and text
* A [[GPRS|packet switched network]] 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]] 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 [[handoff|handover]].

Any phone connects to the network via an RBS ([[Radio Base Station]]) at a corner of the corresponding cell which in turn connects to the [[Mobile switching center]] (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]] (FDMA), [[time-division multiple access]] (TDMA), [[code-division multiple access]] (CDMA), and [[space-division multiple access]] (SDMA).

=== Small cells ===
{{Main|Small cell}}
Small cells, which have a smaller coverage area than base stations, are categorised as follows:
* [[Microcell]] -> less than 2 kilometres,
* [[Picocell]]  -> less than 200 metres,
* [[Femtocell]] -> around 10 metres,
* [[Attocell]]  -> 1–4 metres

=== Cellular handover in mobile phone networks ===
{{Main|Handover}}
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]], multiple CDMA handsets share a specific radio channel. The signals are separated by using a [[pseudorandom noise|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]] inter-frequency handovers and older analog systems such as [[Nordic Mobile Telephone|NMT]] it will typically be impossible to test the target channel directly while communicating. In this case, other techniques have to be used <!--how does NMT handover work exactly?? --> 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 ===
{{Main|Cellular frequencies}}
The effect of frequency on cell coverage means that different frequencies serve better for different uses. Low frequencies, such as 450&nbsp; MHz NMT, serve very well for countryside coverage. [[GSM]] 900 (900&nbsp;MHz) is suitable for light urban coverage.  [[GSM]] 1800 (1.8&nbsp;GHz) starts to be limited by structural walls.  [[UMTS]], at 2.1&nbsp;GHz is quite similar in coverage to [[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]], 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 (telephony)|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]] network:<ref>{{cite web|url=https://www.itu.int/ITU-D/tech/events/2003/slovenia2003/Presentations/Day%203/3.3.1_Chandler.pdf|title=CDMA 2000 and CDMA 450|author=Colin Chandler|page=17|date=3 December 2003|access-date=28 January 2024}}</ref>
{| class="wikitable"
|-
! Frequency (MHz)
! Cell radius (km)
! Cell area (km<sup>2</sup>)
! Relative cell count
|-
| 450
| 48.9
| 7521
| 1
|-
| 950
| 26.9
| 2269
| 3.3
|-
| 1800
| 14.0
| 618
| 12.2
|-
| 2100
| 12.0
| 449
| 16.2
|}

==See also==
[[File:Cellular network standards and generation timeline.svg|thumb|Cellular network standards and generation timeline.]]
Lists and technical information:
* [[Mobile technology|Mobile technologies]]
** [[2G]] networks (the first digital networks, [[1G]] and [[Mobile radio telephone|0G]] were analog):
*** [[GSM]]
****[[Circuit Switched Data]] (CSD)
**** [[GPRS]]
**** [[EDGE (telecommunication)|EDGE]](IMT-SC)
**** [[Evolved EDGE]]
*** [[Digital AMPS]]
****[[Cellular Digital Packet Data]] (CDPD)
*** [[cdmaOne]] (IS-95)
****[[Circuit Switched Data]] (CSD)
*** [[Personal Handy-phone System]] (PHS)
*** [[Personal Digital Cellular]]
** [[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]]
**** [[OFDMA]] (air interface)
***** [[EVDO]]
****** [[SVDO]]
** [[4G]] networks:
*** [[IMT Advanced]]
*** [[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]], [[Space-division multiple access|SDMA]] and [[Beamforming]]

* [[Cellular frequencies]]
** [[CDMA frequency bands]]
** [[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]]
* [[List of mobile phone brands by country]] (manufacturers)

Equipment:
* [[Cellular repeater]]
* [[Cellular router]]
* [[Professional mobile radio]] (PMR)
* [[OpenBTS]]
* [[Remote radio head]]
* [[Base transceiver station|Baseband unit]]
* [[Radio access network]]
* [[Mobile cell sites]]

Other:
* [[Antenna diversity]]
* [[Cellular traffic]]
* [[MIMO]] (multiple-input and multiple-output)
* [[Mobile edge computing]]
* [[Mobile phone radiation and health]]
* [[Network simulation]]
* [[Personal Communications Service]]
* [[Radio resource management]] (RRM)
* [[Routing in cellular networks]]
* [[Signal strength]]
* [[Title 47 of the Code of Federal Regulations]]

== References ==
{{Reflist|30em}}

== Further reading ==
* P. Key, D. Smith. Teletraffic Engineering in a competitive world. Elsevier Science B.V., Amsterdam Netherlands, 1999. {{isbn|978-0444502681}}. Chapter 1 (Plenary) and 3 (mobile).
* William C. Y. Lee, ''[https://books.google.com/books/about/Mobile_Cellular_Telecommunications_Syste.html?id=fS91Sly6vYgC Mobile Cellular Telecommunications Systems]'' (1989), McGraw-Hill. {{isbn|978-0-071-00790-0}}.

== External links ==
* {{cite web|url=http://scis.nova.edu/~raciti/cellular.html|title=CELLULAR TECHNOLOGY|last=Raciti|first=Robert C.|date=July 1995|publisher=Nova Southeastern University|access-date=2 April 2012|archive-url=https://web.archive.org/web/20130715020839/http://scis.nova.edu/~raciti/cellular.html|archive-date=15 July 2013|url-status=dead}}
* [https://www.staracle.com/general/mobileNetworkHistory.php A History of Cellular Networks]
* [https://mystudytech.com/what-are-cellular-networks-1g-to-6g-features-evolution/ What are cellular networks? 1G to 6G Features & Evolution]
* Technical Details with Call Flow about [https://paktechpoint.com/lte-paging-procedure/ LTE Paging Procedure].
{{Mobile telecommunications standards}}
{{Telecommunications}}
{{Authority control}}

{{DEFAULTSORT:Cellular Network}}
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[[Category:Radio resource management]]
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[[Category:Japanese inventions]]
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