Editing Cell site (section)

== Operation ==

=== Range ===

The working range of a cell site (the range which mobile devices connects reliably to the cell site) is not a fixed figure. It will depend on a number of factors, including, but not limited to: 
* Height of antenna over surrounding terrain ([[Line-of-sight propagation]]).
* The frequency of signal in use.
* The transmitter's rated power.
* The required uplink/downlink data rate of the subscriber's device<ref>J. Andrews, A. Gohsh (2007). ''Fundamentals of WiMAX'', p. 43</ref>
* The directional characteristics of the site antenna array.
* Reflection and absorption of radio energy by buildings or vegetation.
* It may also be limited by local geographical or regulatory factors and weather conditions.
* In addition there are timing limitations in some technologies (e.g., even in free space, GSM would be limited to 150&nbsp;km, with 180&nbsp;km being possible with special equipment)

Generally, in areas where there are enough cell sites to cover a wide area, the range of each one will be set to:
* Ensure there is enough overlap for "[[handover]]" to/from other sites (moving the signal for a mobile device from one cell site to another, for those technologies that can handle it - e.g. making a GSM phone call while in a car or train).
* Ensure that the overlap area is not too large, to minimize interference problems with other sites.

In practice, cell sites are grouped in areas of high population density, with the most potential users. Cell phone traffic through a single site is limited by the base station's capacity; of -56 dBm signal there is a finite number of calls or data traffic that a base station can handle at once. This capacity limitation is commonly the factor that determines the spacing of cell mast sites. In suburban areas, masts are commonly spaced {{convert|2–3|km|mi|abbr=on}} apart and in dense urban areas, masts may be as close as 400–800 m apart.<ref>{{Cite web|url=https://www.electronicdesign.com/communications/understanding-small-cell-wireless-backhaul|title=Understanding Small-Cell Wireless Backhaul|date=3 April 2014|website=Electronic Design|access-date=4 December 2019|archive-date=9 August 2020|archive-url=https://web.archive.org/web/20200809003627/http://electronicdesign.com/communications/understanding-small-cell-wireless-backhaul|url-status=live}}</ref>

The ''maximum'' range of a mast (where it is not limited by interference with other masts nearby) depends on the same considerations. In any case the limiting factor is the ability of a low-powered personal cell phone to transmit back to the mast. As a rough guide, based on a tall mast and flat [[terrain]], it may be possible to get between {{convert|50 and 70|km|mi|abbr=on}}. When the terrain is hilly, the maximum distance can vary from as little as {{convert|6 to 8|km|mi|abbr=on}} due to encroachment of intermediate objects into the wide center [[Fresnel zone]] of the signal.<ref>[http://www.arcx.com/sites/faq.htm Frequently Asked PCS Questions] undated, URL retrieved 14 August 2007. {{webarchive |url=https://web.archive.org/web/20060509174612/http://www.arcx.com/sites/faq.htm |date=9 May 2006 }}</ref> Depending on terrain and other circumstances, a GSM Tower can replace between {{convert|2 and 50|mi|km|0|abbr=on|order=flip}} of cabling for fixed wireless networks.<ref>[http://www.accel-networks.com/blog/2009/03/ntia-seeks-input-on-broadband-stimulus.html NTIA Seeks Input on Broadband Stimulus Money] undated, URL retrieved 3 March 2009. {{webarchive |url=https://web.archive.org/web/20091122053748/http://www.accel-networks.com/blog/2009/03/ntia-seeks-input-on-broadband-stimulus.html |date=22 November 2009 }}</ref> In addition, some technologies, such as GSM, have an additional absolute maximum range of {{convert|35|km|mi|abbr=on}}, which is imposed by [[Timing advance|technical limitations]]. CDMA and [[Integrated Digital Enhanced Network|IDEN]] have no such limit defined by timing.

==== Practical example of range ====
* 3G/4G/5G ([[5G NR frequency bands#Frequency Range 1|FR1]]) Mobile base station tower: it is technically possible to cover up to 50–150&nbsp;km. (Macrocell)<ref>{{Cite web|url=https://mobilenetworkguide.com.au/mobile_base_stations.html|title=Mobile Phone Base Stations, How do mobile base stations work, Mobile Base Stations in Australia, Cell Tower, Mobile Phone Tower|website=mobilenetworkguide.com.au|access-date=4 December 2019|archive-date=12 November 2020|archive-url=https://web.archive.org/web/20201112020205/https://mobilenetworkguide.com.au/mobile_base_stations.html|url-status=live}}</ref>
* 5G ([[5G NR frequency bands#Frequency Range 2|FR2]]) Mobile base station: the distances between the 5G base-station is about 250–300&nbsp;m, due to the use of [[Extremely high frequency|millimetre waves]].<ref>{{Cite web|url=https://spectrum.ieee.org/everything-you-need-to-know-about-5g|title=Full Page Reload|website=IEEE Spectrum: Technology, Engineering, and Science News|date=27 January 2017|access-date=4 June 2018|archive-date=15 January 2021|archive-url=https://web.archive.org/web/20210115035415/https://spectrum.ieee.org/video/telecom/wireless/everything-you-need-to-know-about-5g|url-status=live}}</ref>

=== Channel reuse ===
The concept of "maximum" range is misleading in a cellular network. Cellular networks are designed to support many conversations with a limited number of [[radio channel]]s (slices of [[radio frequency spectrum]] necessary to make one conversation) that are licensed to an operator of a cellular service. To overcome this limitation, it is necessary to repeat and [[frequency reuse|reuse]] the same channels at different locations. Just as a car radio changes from one local station to a completely different local station with the same frequency when traveling to another city, the same radio channel gets reused on a cell mast only a few miles away. To do this, the signal of a cell mast is intentionally kept at low power and in many cases tilted downward to limit its reach. This allows covering an area small enough not to have to support more conversations than the available channels can carry. Due to the sectorized arrangement of antennas on a tower, it is possible to vary the strength and angle for each sector depending on the coverage from other towers in the area.

=== Signal limiting factor ===
A cell phone may not work at times because it is too far from a mast, or because the phone is in a location where cell phone signals are [[attenuation|attenuated]] by thick building walls, hills, or other structures. The signals do not need a clear [[Line-of-sight propagation|line of sight]] but greater [[radio interference]] will degrade or eliminate reception. When many people try to use the cell mast at the same time, e.g. during a traffic jam or a sports event, then there will be a signal on the phone display but it is blocked from starting a new connection. The other limiting factor for cell phones is the ability to send a signal from its low powered battery to the cell site. Some cell phones perform better than others under low power or low battery, typically due to the ability to send a good signal from the phone to the mast.

The [[base station controller]] (a central computer that specializes in making phone connections) and the intelligence of the cell phone keeps track of and allows the phone to switch from one mast to the next during conversation. As the user moves towards a mast it picks the strongest signal and releases the mast from which the signal has become weaker; that channel on that mast becomes available to another user.
{{Further|Frequency reuse}}

===Geolocation===

Cellular [[geolocation]] is less precise than by [[GNSS]] (e.g. GPS), but it is available to devices that do not have [[GPS receiver]]s and where the GNSS is not available. The precision of this system varies and is highest where advanced forward link methods are possible and is lowest where only a single cell site can be reached, in which case the location is only known to be within the coverage of that site.

An advanced forward link is where a device is within range of at least three cell sites and where the carrier has implemented timing system use.

Another method is using [[angle of arrival]] (AoA) and it occurs when the device is in range of at least two cell sites, produces intermediate precision. [[Assisted GPS]] uses both satellite and cell phone signals.

In the United States, for emergency calling service using location data (locally called "[[Enhanced 911]]"), it was required that at least 95% of cellular phones in use on 31 December 2005 support such service. Many carriers missed this deadline and were fined by the [[Federal Communications Commission]].<ref>{{Cite web|url=https://www.fiercewireless.com/wireless/sprint-alltel-usc-fined-for-missed-e911-deadline|title=Sprint, Alltel, USC fined for missed e911 deadline|website=FierceWireless|date=31 August 2007|access-date=4 December 2019|archive-date=29 November 2020|archive-url=https://web.archive.org/web/20201129050859/https://www.fiercewireless.com/wireless/sprint-alltel-usc-fined-for-missed-e911-deadline|url-status=live}}</ref>

=== Radio power and health ===
{{Further|Mobile phone radiation and health#Health hazards of base stations}}
According to the U.S. [[Federal Communications Commission]]: "Measurement data obtained from various sources have consistently indicated that 'worst-case' ground-level power densities near typical cellular towers are on the order of 1&nbsp;μW/cm<sup>2</sup> (or 10 mW/m<sup>2</sup>) or less (usually significantly less)."<ref>{{cite book | url = http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf | title = Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields | edition = 4th | date = August 1999 | page = 21 | series = OET Bulletin 56 | access-date = 14 September 2022 | archive-date = 20 October 2011 | archive-url = https://web.archive.org/web/20111020131849/http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf | url-status = live }}</ref>

Cell phones, cell towers, wi-fi, smart meters, digital enhanced cordless telecommunications phones, cordless phones, baby monitors, and other wireless devices all emit non-ionizing radio frequencies, which the [[World Health Organization]] (WHO) has classified as a "potential" [[carcinogen]],<ref name="Hardell">{{cite journal | last1=Hardell |first1=Lennart |title=World Health Organization, Radiofrequency Radiation and Health—A Hard Nut to Crack (Review) |journal=International Journal of Oncology |date=21 June 2017 |volume=51 |issue=August 2017 |pages=405–13 |doi=10.3892/ijo.2017.4046 |pmid=28656257 |pmc=5504984 }}.</ref> According to the U.S. [[National Cancer Institute]], "No mechanism by which ELF-EMFs or radiofrequency radiation could cause  cancer has been identified."<ref>{{Cite web|url=https://www.cancer.gov/about-cancer/causes-prevention/risk/radiation/electromagnetic-fields-fact-sheet|title=Electromagnetic Fields and Cancer|date=7 January 2019|website=National Cancer Institute|access-date=26 February 2019|archive-date=5 March 2020|archive-url=https://web.archive.org/web/20200305192138/https://www.cancer.gov/about-cancer/causes-prevention/risk/radiation/electromagnetic-fields-fact-sheet|url-status=live}}</ref>

According to the U.S. [[Food and Drug Administration]], "Scientific consensus shows that non-ionizing radiation is not a carcinogen and, at or below the radio frequency exposure limits set by the FCC, non-ionizing radiation has not been shown to cause any harm to people."<ref>{{cite web | url=https://www.fda.gov/radiation-emitting-products/cell-phones/radio-frequency-radiation-and-cell-phones | title=Radio Frequency Radiation and Cell Phones | website=U.S. Food and Drug Administration | date=30 May 2022 | access-date=14 September 2022 | archive-date=30 September 2022 | archive-url=https://web.archive.org/web/20220930124337/https://www.fda.gov/radiation-emitting-products/cell-phones/radio-frequency-radiation-and-cell-phones | url-status=dead }}</ref>