C-systems Energy Resources LLC

A cell site is a cellular telephone site where antennas and electronic communications equipment are placed, usually on a radio mast, tower or other high place, to create a cell (or adjacent cells) in a cellular network. The elevated structure typically supports antennas, 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.

A cell site is sometimes incorrectly called a "cell tower", even if the cell site antennas are mounted on a building rather than a tower. In fact, it's likely that a majority of cell sites worldwide are located on structures other than towers. In GSM networks, the correct term is Base Transceiver Station (BTS), and colloquial British English 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).

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.

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 emergency power. More sites use internal-combustion-engine-driven generator sets. 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. 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:

• Solar power generator
• Wind generator
• Electro-chemical generator fuel cells

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 fuels 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.

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

• Height of antenna over surrounding terrain (Line-of-sight propagation).
• The frequency of signal in use.
• Timing limitations in some technologies (e.g., GSM is limited to 35 km, with 70 km being possible with special equipment)
• The transmitter's rated power.
• The required uplink/downlink data rate of the subscriber's device
• 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.

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; there is a finite number of calls or data traffic that a base station 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.

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 (22 mi), which is imposed by technical limitations. CDMA and IDEN 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 (5.0 mi) due to encroachment of intermediate objects into the wide center fresnel zone of the signal. Depending on terrain and other circumstances, a GSM Tower can replace between 2 and 50 miles (80 km) of cabling for fixed wireless networks.