Cell site
Overview
 

A cell site is a term used to describe a site where antennas and electronic communications equipment are placed, usually on a radio mast, tower
Radio masts and towers
Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. They are among the tallest man-made structures...

 or other high place, to create a cell in a cellular network
Cellular network
A cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area...

. The elevated structure typically supports antennas, and one or more sets of transmitter/receivers transceiver
Transceiver
A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...

s, digital signal processor
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...

s, control electronics, a GPS receiver for timing (for CDMA2000
CDMA2000
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...

/IS-95
IS-95
Interim Standard 95 is the first CDMA-based digital cellular standard by Qualcomm. The brand name for IS-95 is cdmaOne. IS-95 is also known as TIA-EIA-95....

 or GSM systems), primary and backup electrical power sources, and sheltering.

A cell site is sometimes called a "cell tower", even if the cell site antennas are mounted on a building rather than a tower.
Encyclopedia

A cell site is a term used to describe a site where antennas and electronic communications equipment are placed, usually on a radio mast, tower
Radio masts and towers
Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. They are among the tallest man-made structures...

 or other high place, to create a cell in a cellular network
Cellular network
A cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area...

. The elevated structure typically supports antennas, and one or more sets of transmitter/receivers transceiver
Transceiver
A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...

s, digital signal processor
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...

s, control electronics, a GPS receiver for timing (for CDMA2000
CDMA2000
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...

/IS-95
IS-95
Interim Standard 95 is the first CDMA-based digital cellular standard by Qualcomm. The brand name for IS-95 is cdmaOne. IS-95 is also known as TIA-EIA-95....

 or GSM systems), primary and backup electrical power sources, and sheltering.

A cell site is sometimes called a "cell tower", even if the cell site antennas are mounted on a building rather than a tower. In GSM networks, the technically correct term is Base Transceiver Station
Base Transceiver Station
A base transceiver station or cell site is a piece of equipment that facilitates wireless communication between user equipment and a network. UEs are devices like mobile phones , WLL phones, computers with wireless internet connectivity, WiFi and WiMAX gadgets etc...

 (BTS), and colloquial British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

 synonyms are "mobile phone mast" or "base station
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...

". 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
CDMA2000
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...

 or GSM, for example).

Some cities require that cell sites be inconspicuous, for example blended with the surrounding area. 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.

Range

The working range of a cell site - the range within which mobile devices can connect to it reliably - is not a fixed figure. It will depend on a number of factors, including
  • The frequency of signal in use (i.e. the underlying technology).
  • The transmitter's rated power.
  • The required uplink/downlink data rate of the subscriber's device
  • The transmitter's size.
  • The array setup of panels may cause the transmitter to be directional
    Directional antenna
    A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....

     or omni-directional
    Omnidirectional antenna
    In radio communication, an omnidirectional antenna is an antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often...

    .
  • It may also be limited by local geographical or regulatory factors and weather conditions.


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
    Handover
    In cellular telecommunications, the term handover or handoff refers to the process of transferring an ongoing call or data session from one channel connected to the core network to another...

    " 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 cell mast is limited by the mast's capacity; there is a finite number of calls or data traffic that a mast can handle at once. This limitation is another factor affecting 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. Cell masts always reserve part of their available bandwidth for emergency calls.

The maximum range of a mast (where it is not limited by interference with other masts nearby) depends on the same circumstances. Some technologies, such as GSM, normally have a fixed maximum range of 35 kilometres (21.7 mi), which is imposed by technical limitations
Timing advance
In the GSM cellular mobile phone standard, timing advance value corresponds to the length of time a signal takes to reach the base station from a mobile phone. GSM uses TDMA technology in the radio interface to share a single frequency between several users, assigning sequential timeslots to the...

. CDMA and IDEN
Integrated Digital Enhanced Network
Integrated Digital Enhanced Network is a mobile telecommunications technology, developed by Motorola, which provides its users the benefits of a trunked radio and a cellular telephone...

 have no built-in limit, but 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 is possible to get between 50 to 70 km (30–45 miles). When the terrain is hilly, the maximum distance can vary from as little as 5 kilometres (3.1 mi) to 8 kilometres (5 mi) due to encroachment of intermediate objects into the wide center fresnel zone
Fresnel zone
In optics and radio communications , a Fresnel zone , named for physicist Augustin-Jean Fresnel, is one of a number of concentric ellipsoids which define volumes in the radiation pattern of a circular aperture...

 of the signal. Depending on terrain and other circumstances, a GSM Tower can replace between 2 and 50 miles (80.5 km) of cabling for fixed wireless networks.

Channel reuse

The concept of "maximum" range is misleading, however, in a cellular network. Cellular networks are designed to support many conversations with a limited number of radio channels (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 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 you travel 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 many cases tilted downward to limit its area. This allows it to cover 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 of each sector depending on the coverage of other towers in view of the sector.

A cellphone 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 attenuated by thick building walls, hills or other structures. The signals do not need a clear line of sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...

 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 of the cell phone to send a signal from its low powered battery to the mast. Some cellphones 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 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.

Geolocation

Cellular geolocation
Geolocation
Geolocation is the identification of the real-world geographic location of an object, such as a radar, mobile phone or an Internet-connected computer terminal...

 is less precise than by GPS, but it is available to devices that do not have GPS receivers and where the GPS is not available. The precision of this system varies widely. Precision is highest where advanced forward link methods are possible (where a device is within range of at least three cell sites and where the carrier has implemented timing system use) and 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. Another method using angle of arrival
Angle of arrival
Angle of arrival measurement is a method for determining the direction of propagation of a radio-frequency wave incident on an antenna array...

 (AoA), possible when in range of at least two cell sites, produces intermediate precision.
In the United States, for emergency calling service using location data (locally called "Enhanced 911
Enhanced 911
Enhanced 911, E-911 or E911 in North America is one example of the modern evolution of telecommunications based system meant as an easy way to link people experiencing an emergency with the public resources that can help. The dial-three-digits concept first originated in the United Kingdom in 1937....

"), 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
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...

.

Radio power and health

The U.S. government agency, the FCC, says:

"For example, 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)."

Temporary set-up

Although cell antennas are normally attached to permanent structures, carriers also maintain fleets of vehicles, called cells-on-wheels
Cell On Wheels
A cell on wheels, usually referred to as a COW, is a mobile cell site that consists of a cellular antenna tower and electronic radio transceiver equipment on a truck or trailer, designed to be part of a cellular network.-Expanded or emergency service:...

 (COWs), that serve as temporary cell sites. A generator may be included for use where network electrical power isn't available, and the system may have a wireless backhaul
Backhaul (telecommunications)
In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network, or backbone, of the network and the small subnetworks at the "edge" of the entire hierarchical network...

 link allowing use where a wired link is not available.

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.

Off Grid Systems

Some cell sites can work off grid (that is without electrical power from the grid).
Fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...

 backup power systems are added to critical cell sites to provide emergency power. More sites use internal-combustion-engine-driven generator sets.
In places distant from power lines, base stations are generally powered by generators. This solution, in addition to being a source of pollution (atmospheric, acoustic, etc.) is often used in areas protected by environment and landscape conservation and adds operating expense
Operating expense
An operating expense, operating expenditure, operational expense, operational expenditure or OPEX is an ongoing cost for running a product, business, or system . Its counterpart, a capital expenditure , is the cost of developing or providing non-consumable parts for the product or system...

.
Renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

 can be applied for reliability and energy autonomy.
This solution in addition to being ecologically correct, is based on innovative technical solutions that render it economically competitive in respect to traditional power systems.

Camouflage

There is often local opposition to new masts for reasons of safety
Mobile phone radiation and health
The effect of mobile phone radiation on human health is the subject of recent interest and study, as a result of the enormous increase in mobile phone usage throughout the world . Mobile phones use electromagnetic radiation in the microwave range...

 and appearance. The latter is sometimes tackled by disguising the mast as something else, such as a flag pole, street lamp, or a tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

 (i.e. palm trees, pine trees, cypress..) or rooftop structures or urban features such as chimneys or panels.

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 "Pseudpinus 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.

See also

  • Cellular network
    Cellular network
    A cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area...

  • Node B
  • OpenBTS
    OpenBTS
    OpenBTS is a software-based GSM access point, allowing standard GSM-compatible mobile phones to make telephone calls without using existing telecommunication providers' networks...

  • Mobile phone radiation and health
    Mobile phone radiation and health
    The effect of mobile phone radiation on human health is the subject of recent interest and study, as a result of the enormous increase in mobile phone usage throughout the world . Mobile phones use electromagnetic radiation in the microwave range...

  • Telecom infrastructure sharing
    Telecom infrastructure sharing
    Due to economy of scale property of telecommunication industry, sharing of telecom infrastructure among telecom service providers is becoming the requirement and process of business in the telecom industry where competitors are becoming partners in order to lower their increasing investments...

  • Concealed cell sites
  • Base transceiver station
    Base Transceiver Station
    A base transceiver station or cell site is a piece of equipment that facilitates wireless communication between user equipment and a network. UEs are devices like mobile phones , WLL phones, computers with wireless internet connectivity, WiFi and WiMAX gadgets etc...

  • Radio masts and towers
    Radio masts and towers
    Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. They are among the tallest man-made structures...

  • Mobile cell sites
    Mobile cell sites
    The mobile cell sites are infrastructures transportable on trucks, allowing fast and easy installation in restricted spaces. Their use is strategic for the rapid expansion of cellular networks putting into service point to point radio connections, as well as supporting sudden increases of mobile...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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