CELL SITE

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 transceivers, digital signal processors, and control electronics, a GPS receiver for timing (for CDMA2000/IS-95 or GSM systems), primary and backup electrical power sources, and shelter.

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).
Some cities require that cell sites be inconspicuous; they can be blended with the surrounding area or mounted on buildings or advertising towers. Preserved trees capes 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.
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. 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, his phone is automatically "handed off" to the new cell, and assigned a new set of frequencies, and subsequently communicates with the new cell's antenna. This background handoff process is transparent 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, 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 working range of a cell site (the range which mobile devices connect 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 transmitters 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.
In addition there are timing limitations in some technologies (e.g., even in free space, GSM would be limited to 35 km, with 70 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; 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.
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 5 kilometers (3.1 mi) to 8 kilometers (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. In addition, some technologies, such as GSM, have an additional absolute maximum range of 35 kilometers (22 mi), which is imposed by technical limitations. CDMA and IDEN have no such limit defined by timing.
3G/4G Mobile base station tower: it is technically possible to cover up to 50 km-150 km. (Macro cell)
5G Mobile base station: the distances between the 5G base-station is about 250-300 m due to the millimeter waves of 5G frequency.
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.