Cell site

Last updated

Cell towers
Cell tower aerial.jpg
TypeCellular telephone site
First production 20th century
Cellular lattice tower Lattice cell tower-2.jpg
Cellular lattice tower
A cell tower in the bush in Africa Communications Mast in the African Bush.jpg
A cell tower in the bush in Africa

A cell site, cell phone tower, cell base tower, or cellular base station is a cellular-enabled mobile device site where antennas 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 antenna[ clarification needed ] and one or more sets of transmitter/receivers transceivers, 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. [1]

Contents

Multiple cellular providers often save money by mounting their antennas on a common shared mast; since separate systems use different frequencies, antennas can be located close together without interfering with each other. Some provider companies operate multiple cellular networks and similarly use colocated base stations for two or more cellular networks, (CDMA2000 or GSM, for example).

Cell sites are sometimes required to be inconspicuous; [2] they may be blended with the surrounding area [3] or mounted on buildings [4] or advertising towers.[ citation needed ] Preserved treescapes can often hide cell towers inside an artificial or preserved tree. These installations are generally referred to as concealed cell sites or stealth cell sites. [2]

Overview

A cellular network is a network of handheld mobile phones (cell phones) in which each phone communicates with the telephone network by radio waves through a local antenna at a cellular base station (cell site). The coverage area in which service is provided is divided into a mosaic of small geographical areas called "cells", each served by a separate low power multichannel transceiver and antenna at a base station. All the cell phones within a cell communicate with the system through that cell's antenna, on separate frequency channels assigned by the base station from a common pool of frequencies used by the system.

The purpose of cellular organization is to conserve radio bandwidth by frequency reuse; the low power radio signals used within each cell do not travel far beyond the cell, so the radio channels can be reused in geographically separated cells. When a mobile user moves from one cell to another, their phone is automatically "handed off" to the new cell's antenna, and assigned a new set of frequencies, and subsequently communicates with this antenna. This background handoff process is imperceptible to the user and can occur in the middle of a phone call without any service interruption. Each cell phone has an automated full duplex digital transceiver and communicates with the cell antenna over two digital radio channels in the UHF or microwave band, one for each direction of the bidirectional conversation, plus a control channel which handles registering the phone with the network, dialing, and the handoff process.

Typically a cell tower is located at the edge of one or more cells and covers multiple cells using directional antennas. A common geometry is to locate the cell site at the intersection of three adjacent cells, with three antennas at 120° angles each covering one cell. The type of antenna used for cellular base stations (vertical white rectangles in pictures), called a sector antenna, usually consists of a vertical collinear array of dipoles. It has a flat fan-shaped radiation pattern, which is tilted slightly down to cover the cell area without radiating at higher angles into further off cells which reuse the same frequencies. The elevation angle of the antenna must be carefully adjusted, so the beam covers the entire cell without radiating too far. In modern sector antennas beam tilt can usually be adjusted electronically, to avoid the necessity of a lineman climbing the tower to mechanically tilt the antenna when adjustment is needed.

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:

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; 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 2–3 km (1.2–1.9 mi) apart and in dense urban areas, masts may be as close as 400–800 m apart. [6]

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 (31 and 43 mi). When the terrain is hilly, the maximum distance can vary from as little as 6 to 8 km (3.7 to 5.0 mi) due to encroachment of intermediate objects into the wide center Fresnel zone of the signal. [7] Depending on terrain and other circumstances, a GSM Tower can replace between 3 and 80 km (2 and 50 mi) of cabling for fixed wireless networks. [8] In addition, some technologies, such as GSM, have an additional absolute maximum range of 35 km (22 mi), which is imposed by technical limitations. CDMA and IDEN have no such limit defined by timing.

Practical example of range

  • 3G/4G/5G (FR1) Mobile base station tower: it is technically possible to cover up to 50–150 km. (Macrocell) [9]
  • 5G (FR2) Mobile base station: the distances between the 5G base-station is about 250–300 m, due to the use of millimetre waves. [10]

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 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 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 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 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 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 is less precise than by GNSS (e.g. GPS), but it is available to devices that do not have GPS receivers 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. [11]

Radio power and health

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 μW/cm2 (or 10 mW/m2) or less (usually significantly less)." [12]

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, [13] According to the U.S. National Cancer Institute, "No mechanism by which ELF-EMFs or radiofrequency radiation could cause cancer has been identified." [14]

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." [15]

Temporary sites

A mobile antenna used during the 2021 Cumbre Vieja volcanic eruption At La Palma 2021 1880.jpg
A mobile antenna used during the 2021 Cumbre Vieja volcanic eruption

Although cell antennas are normally attached to permanent structures, carriers also maintain fleets of vehicles, called cells-on-wheels (COWs), that serve as temporary cell sites. A generator may be included for use where network electrical power is not available, and the system may have a wireless backhaul 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.

Cell on wheels (COW) Cell on wheels.jpg
Cell on wheels (COW)

Employment

Cell site workers are called tower climbers or transmission tower workers. Transmission tower workers often work at heights of up to 460 m (1,500 ft), performing installation, maintenance and repair work for cellular phone and other wireless communications companies.

Spy agency setup

According to documents leaked to Der Spiegel, the NSA sells a $40,000 "active GSM base station" to be used as a tool to mimic a mobile phone tower and thus monitor cell phones. [16]

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. [17] [18]

Off-grid systems

An off-grid cell site is not connected to the public electrical grid. Usually the system is off-the-grid because of difficult access or lack of infrastructure. Fuel cell or other backup power systems are added to critical cell sites to provide day-to-day and emergency power. Traditionally, sites have used internal-combustion-engine-driven generator sets, [19] [20] however, being less efficient than public power, they increase operating expense and are a source of pollution (atmospheric, acoustic, etc.) and some are in areas protected by environment and landscape conservation.

Renewable sources, such as solar power and wind power may be available where cell sites are placed. The first off-grid mast in the UK was installed in 2022 in Eglwyswrw, Wales. [21] This can reduce the cost of fuel to the cell site or telecom tower by up to 75%. 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 two days of self-sufficiency, also known as autonomy, 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 ten 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.

Camouflage

There is often local opposition to new masts for reasons of safety and appearance. The latter is sometimes tackled by disguising the mast as something else, such as a flag pole, street lamp, or a tree (e.g. 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 "Pseudopinus telephoneyensis" for a mast disguised as a pine tree. [22] 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.

Miniature

Researchers at Alcatel-Lucent have developed a cell site called lightRadio that fits in the palm of hand. It is the size of a Rubik's cube. It is capable of relaying 2G, 3G and 4G signals. They are more energy efficient and deliver broadband more efficiently than current cell sites. They could be used in very populated urban areas to make room for more radio space. [23]

Water tower cellular

Mauston water tower with cellular tower on top.jpg
Water tower with cellular tower on top in Mauston, Wisconsin
Water tower cellular.webp
Water tower cellular around the neck in Barrington, Illinois

Cellular companies sign leases with local governments to place cellular antennas on water towers. [24]

See also

Related Research Articles

<span class="mw-page-title-main">GSM</span> Cellular telephone network standard

The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile devices such as mobile phones and tablets. GSM is also a trade mark owned by the GSM Association. GSM may also refer to the Full Rate voice codec.

<span class="mw-page-title-main">Time-division multiple access</span> Channel access method for networks using a shared communications medium

Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium while using only a part of its channel capacity. Dynamic TDMA is a TDMA variant that dynamically reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic demand of each data stream.

<span class="mw-page-title-main">Wireless network</span> Computer network not fully connected by cables

A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking allows homes, telecommunications networks and business installations to avoid the costly process of introducing cables into a building, or as a connection between various equipment locations. Admin telecommunications networks are generally implemented and administered using radio communication. This implementation takes place at the physical level (layer) of the OSI model network structure.

<span class="mw-page-title-main">Ultra high frequency</span> Electromagnetic spectrum 300–3000 MHz

Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter. Radio waves with frequencies above the UHF band fall into the super-high frequency (SHF) or microwave frequency range. Lower frequency signals fall into the VHF or lower bands. UHF radio waves propagate mainly by line of sight; they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception. They are used for television broadcasting, cell phones, satellite communication including GPS, personal radio services including Wi-Fi and Bluetooth, walkie-talkies, cordless phones, satellite phones, and numerous other applications.

<span class="mw-page-title-main">Base station</span> Type of radio station

Base station is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a "land station in the land mobile service."

<span class="mw-page-title-main">Base station subsystem</span> Section of cellular telephone network

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 and the network switching subsystem. The BSS carries out transcoding of speech channels, allocation of radio channels to mobile phones, paging, transmission and reception over the air interface and many other tasks related to the radio network.

A base transceiver station (BTS) or a baseband unit (BBU) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phones (handsets), WLL phones, computers with wireless Internet connectivity, or antennas mounted on buildings or telecommunication towers. The network can be that of any of the wireless communication technologies like GSM, CDMA, wireless local loop, Wi-Fi, WiMAX or other wide area network (WAN) technology.

<span class="mw-page-title-main">Cellular network</span> Communication network

A cellular network or mobile network is a telecommunications network where the link to and from end nodes is wireless and the network is distributed over land areas called cells, each served by at least one fixed-location transceiver. 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.

<span class="mw-page-title-main">Mobile telephony</span> Provision of telephone services to phones

Mobile telephony is the provision of telephone services to mobile phones rather than fixed-location phones. Telephony is supposed to specifically point to a voice-only service or connection, though sometimes the line may blur.

<span class="mw-page-title-main">History of mobile phones</span> Mobile communication devices

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<span class="mw-page-title-main">Wireless device radiation and health</span> Health Phenomenon

The antennas contained in mobile phones, including smartphones, emit radiofrequency (RF) radiation ; the parts of the head or body nearest to the antenna can absorb this energy and convert it to heat. Since at least the 1990s, scientists have researched whether the now-ubiquitous radiation associated with mobile phone antennas or cell phone towers is affecting human health. Mobile phone networks use various bands of RF radiation, some of which overlap with the microwave range. Other digital wireless systems, such as data communication networks, produce similar radiation.

<span class="mw-page-title-main">Mobile phone tracking</span> Identifying the location of a mobile phone

Mobile phone tracking is a process for identifying the location of a mobile phone, whether stationary or moving. Localization may be affected by a number of technologies, such as the multilateration of radio signals between (several) cell towers of the network and the phone or by simply using GNSS. To locate a mobile phone using multilateration of mobile radio signals, the phone must emit at least the idle signal to contact nearby antenna towers and does not require an active call. The Global System for Mobile Communications (GSM) is based on the phone's signal strength to nearby antenna masts.

The air interface, or access mode, is the communication link between the two stations in mobile or wireless communication. The air interface involves both the physical and data link layers of the OSI model for a connection.

<span class="mw-page-title-main">Node B</span> Base transceiver stations that serve 3G-enabled user equipment specifically

Node B is the telecommunications node for mobile communication networks, namely those that adhere to the UMTS standard. The Node B provides the connection between mobile phones (UEs) and the wider telephone network. UMTS is the dominating 3G standard.

A cellular repeater is a type of bi-directional amplifier used to improve cell phone reception. A cellular repeater system commonly consists of a donor antenna that receives and transmits signal from nearby cell towers, coaxial cables, a signal amplifier, and an indoor rebroadcast antenna.

<span class="mw-page-title-main">Comparison of mobile phone standards</span>

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<span class="mw-page-title-main">Mobile phone signal</span> Signal strength received by a phone from a network

A mobile phone signal is the signal strength received by a mobile phone from a cellular network. Depending on various factors, such as proximity to a tower, any obstructions such as buildings or trees, etc. this signal strength will vary. Most mobile devices use a set of bars of increasing height to display the approximate strength of this received signal to the mobile phone user. Traditionally five bars are used.

A macrocell or macrosite is a cell in a mobile phone network that provides radio coverage served by a high power cell site. Generally, macrocells provide coverage larger than microcell. The antennas for macrocells are mounted on ground-based masts, rooftops and other existing structures, at a height that provides a clear view over the surrounding buildings and terrain. Macrocell base stations have power outputs of typically tens of watts. Macrocell performance can be increased by increasing the efficiency of the transceiver.

<span class="mw-page-title-main">Remote radio head</span> Type of radio used in wireless telecommunications networks

A remote radio head (RRH), also called a remote radio unit (RRU) in wireless networks, is a remote radio transceiver that connects to an operator radio control panel via electrical or wireless interface. When used to describe aircraft radio cockpit radio systems, the control panel is often called the radio head.

<span class="mw-page-title-main">Stingray phone tracker</span> Cellular phone surveillance device

The StingRay is an IMSI-catcher, a cellular phone surveillance device, manufactured by Harris Corporation. Initially developed for the military and intelligence community, the StingRay and similar Harris devices are in widespread use by local and state law enforcement agencies across Canada, the United States, and in the United Kingdom. Stingray has also become a generic name to describe these kinds of devices.

References

  1. ↑ Raj Krithin Katla (10 November 2020). "Learn about what is on a cell tower". Medium. Techno Chronicle Magazine. Retrieved 21 August 2024.
  2. 1 2 Jackson Chung (10 August 2013). "24 Cell Phone Towers Disguised as Everyday Things". TechBlog. Honekai Media. Retrieved 21 August 2024.
  3. ↑ Rubenstein, Carin (11 July 2004). "The Girded, The Bland And the Prickly". The New York Times. Archived from the original on 25 June 2020. Retrieved 18 February 2017.
  4. ↑ Buckley, Cara; Richtel, Matt (20 August 2010). "Good Cellphone Service Comes at a Price". The New York Times. Archived from the original on 4 December 2019. Retrieved 18 February 2017.
  5. ↑ J. Andrews, A. Gohsh (2007). Fundamentals of WiMAX, p. 43
  6. ↑ "Understanding Small-Cell Wireless Backhaul". Electronic Design. 3 April 2014. Archived from the original on 9 August 2020. Retrieved 4 December 2019.
  7. ↑ Frequently Asked PCS Questions undated, URL retrieved 14 August 2007. Archived 9 May 2006 at the Wayback Machine
  8. ↑ NTIA Seeks Input on Broadband Stimulus Money undated, URL retrieved 3 March 2009. Archived 22 November 2009 at the Wayback Machine
  9. ↑ "Mobile Phone Base Stations, How do mobile base stations work, Mobile Base Stations in Australia, Cell Tower, Mobile Phone Tower". mobilenetworkguide.com.au. Archived from the original on 12 November 2020. Retrieved 4 December 2019.
  10. ↑ "Full Page Reload". IEEE Spectrum: Technology, Engineering, and Science News. 27 January 2017. Archived from the original on 15 January 2021. Retrieved 4 June 2018.
  11. ↑ "Sprint, Alltel, USC fined for missed e911 deadline". FierceWireless. 31 August 2007. Archived from the original on 29 November 2020. Retrieved 4 December 2019.
  12. ↑ Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields (PDF). OET Bulletin 56 (4th ed.). August 1999. p. 21. Archived (PDF) from the original on 20 October 2011. Retrieved 14 September 2022.
  13. ↑ Hardell, Lennart (21 June 2017). "World Health Organization, Radiofrequency Radiation and Health—A Hard Nut to Crack (Review)". International Journal of Oncology. 51 (August 2017): 405–13. doi:10.3892/ijo.2017.4046. PMC   5504984 . PMID   28656257..
  14. ↑ "Electromagnetic Fields and Cancer". National Cancer Institute. 7 January 2019. Archived from the original on 5 March 2020. Retrieved 26 February 2019.
  15. ↑ "Radio Frequency Radiation and Cell Phones". U.S. Food and Drug Administration. 30 May 2022. Archived from the original on 30 September 2022. Retrieved 14 September 2022.
  16. ↑ Appelbaum, Jacob; Horchert, Judith; Stöcker, Christian (29 December 2013). "Shopping for Spy Gear: Catalog Advertises NSA Toolbox". Der Spiegel. Archived from the original on 16 December 2020. Retrieved 4 December 2019– via Spiegel Online.
  17. ↑ Devlin Barrett (13 November 2014). "Americans' Cellphones Targeted in Secret U.S. Spy Program: Devices on Planes that Mimic Cellphone Towers Used to Target Criminals, but Also Sift Through Thousands of Other Phones". The Wall Street Journal. Archived from the original on 6 June 2018. Retrieved 14 November 2014.
  18. ↑ Kate Knibbs (13 November 2014). "WSJ: A Secret U.S. Spy Program Is Using Planes to Target Cell Phones". Gizmodo. Archived from the original on 30 November 2020. Retrieved 14 November 2014.
  19. ↑ Ballard fuel cells to power telecom backup power units for Motorola Archived 6 July 2011 at the Wayback Machine
  20. ↑ "India telecoms to get fuel cell power". Archived from the original on 26 November 2010.
  21. ↑ "Pembrokeshire: Wind and solar powered phone mast in UK first". BBC News. 15 June 2022. Archived from the original on 15 June 2022. Retrieved 15 June 2022.
  22. ↑ BOWEN, Humphry (1 January 1999). "NEW CONIFER IN THE BRITISH ISLES?" (PDF). BSBI NEWS. No. January 1999. UK. p. 51. Archived from the original (PDF) on 26 July 2011. Retrieved 1 November 2023.
  23. ↑ The tiny cube that could cut your cell phone bill Archived 12 November 2020 at the Wayback Machine , CNN Money, 21 March 2011, David Goldman
  24. ↑ "Water tower-based cell antennas provide municipal revenues, better phone service". 26 July 2011.
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