A cell site or cell tower is a cellular-enabled mobile device site where antennae and electronic communications equipment are placed — typically on a radio mast, tower, or other raised structure — to create a cell (or adjacent cells) in a cellular network. The raised structure typically supports antennae and one or more sets of transmitter/receivers , digital signal processors, control electronics, a GPS receiver for timing (for CDMA2000/IS-95 or GSM systems), primary and backup electrical power sources, and sheltering.
In Global System for Mobile Communications (GSM) networks, the correct term is Base Transceiver Station (BTS), and colloquial synonyms are "mobile phone mast" or "base station". The term "base station site" might better reflect the increasing co-location of multiple mobile operators, and therefore multiple base stations, at a single site. Depending on an operator's technology, even a site hosting just a single mobile operator may house multiple base stations, each to serve a different air interface technology (CDMA2000 or GSM, for example).
/ref> or advertising towers. Preserved treescapes can often hide cell towers inside an artificial tree or preserved tree. These installations are generally referred to as concealed cell sites or stealth cell sites.
Generally, in areas where there are enough cell sites to cover a wide area, the range of each one will be set to:
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; 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 1–2 miles (2–3 km) apart and in dense urban areas, masts may be as close as ¼-½ mile (400–800 m) apart.http://www.electronicdesign.com/communications/understanding-small-cell-wireless-backhaul
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 50 and 70 km (30–45 miles). When the terrain is hilly, the maximum distance can vary from as little as to due to encroachment of intermediate objects into the wide center fresnel zone of the signal. Frequently Asked PCS Questions undated, URL retrieved 14 August 2007. Depending on terrain and other circumstances, a GSM Tower can replace between 2 and of cabling for fixed wireless networks. NTIA Seeks Input on Broadband Stimulus Money undated, URL retrieved 3 March 2009. In addition, some technologies, such as GSM, have an additional absolute maximum range of , which is imposed by Timing advance. CDMA and IDEN have no such limit defined by timing.
The base station controller (a central computer that specializes in making phone connections) and the intelligence of the cellphone 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.
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.http://www.fiercewireless.com/story/sprint-alltel-usc-fined-missed-e911-deadline/2007-08-31
"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 µW/cm2 or less (usually significantly less)." Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields Fourth Edition. FCC. August 1999. Page 21. Retrieved 7 April 2013
Cell phones, cell towers, wi-fi, smart meters, DECT phones, cordless phones, baby monitors and other wireless devices all emit non ionizing radio frequencies, which the World Health Organization (WHO) has just classified as a potential carcinogen. It should be noted however that this is classified as limited evidence available for carcinogenicity, which by definition states "chance, bias or confounding could not be ruled out with reasonable confidence." Retrieved 20 October 2014
COWs are also used at permanent cell sites—as temporary replacements for damaged equipment, during planned outages, and to augment capacity such as during conventions.
In November 2014, the Wall Street Journal reported that the Technical Operations Group of the U.S. Marshals utilizes spy devices, known as "dirtboxes", to mimic powerful cell tower signals. Such devices are designed to cause mobile phones to switch over to the tower, as it is the strongest signal within reach. The devices are placed on airplanes to effectively create a "dragnet", gathering data about phones as the planes travel above populated areas.
Renewable sources, such as solar power and wind powerSuch as Wind-it tower may be available where cell sites are placed. They can be backed up by a fuel generator system which allows the cell site to work when the renewable sources are not enough. One such energy production system consists of:
Electrical energy from intermittent sources is stored in secondary batteries which are usually designed to have an average of 5 days of self-sufficiency, to allow time for maintenance personnel to arrive at site when a repair is needed.
The renewable energy systems supply electrical power when available. The fuel cells are activated only when the natural sources are not enough to supply the energy the system needs. The emergency power supply (the fuel cells) is designed to last an average of 10 days. In this way the structure is completely self-sufficient: this enables the maintenance team to pay only few visits to the site, since it is usually hard to get to.
These concealed cell sites can distinguish themselves by foliage shape and bark type. The foliage of all these antennas is composed of leaves made of plastic material accurately designed, taking into consideration quantity, shape and array suitable to completely conceal the antennas and all accessory parts in a natural manner. The materials used guarantee absolute radio-electric transparency and resistance to UVA rays. Nicknames include "monopalm" for a monopole disguised as a palm tree or "Pseudopinus telephoneyensis" for a mast disguised as a pine tree. In monopoles, the directional antennas are sometimes hidden in a plastic housing near the top of the pole so that the crossbars can be eliminated.
Rooftop structures such as concealment chimneys or panels, 6 to 12 meters high, may conceal one or more mobile telephone operators on the same station. Roofmask panels can be fixed to existing rooftop structures, restyling them quickly and cheaply.
Mobile telephone base stations are becoming a contemporary symbol, connected and intertwining with material and immaterial networks. Telestyles are architecturally blended cell towers, the result of cooperation with designers and architects.