"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 type of signal in use (i.e. the underlying technology), similar to the fact that AM radio waves reach further than FM radio waves. - The transmitter's rated power. - The transmitter's size. - The array setup of panels may cause the transmitter to be directional or omni-directional. - 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 cell mast is limited by the mast's capacity; there is a finite number of calls 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 apart and in dense urban areas, masts may be as close as ¼-½ mile 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, have a fixed maximum range of 40km (25 miles), which is imposed by technical limitations. CDMA and iDEN have no built-in limit, but the limiting factor is really 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). The concept of "maximum" range is misleading, however, in a cellular network. Cellular networks are designed to create a mass communication solution from a limited amount of 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. Just as a station on a car radio changes to a completely different local station 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 tilting downward to limit its area. The area sometimes needs to be limited when a large number of people live, drive or work near a particular mast; the range of this mast has to limited so that it covers an area small enough not to have to support more conversations than the available channels can carry." Source and further information: http://en.wikipedia.org/wiki/Cell_site Further information: http://en.wikipedia.org/wiki/Base_Transceiver_Station