Editing Cellular network (section)

== Frequency reuse ==
The key characteristic of a cellular network is the ability to reuse frequencies to increase both coverage and capacity.  As described above, adjacent cells must use different frequencies, however, there is no problem with two cells sufficiently far apart operating on the same frequency, provided the masts and cellular network users' equipment do not transmit with too much power.<ref name=Zander/>

The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, ''D'' is calculated as

:<math>D=R\sqrt{3N}</math>,

where ''R'' is the cell radius and ''N'' is the number of cells per cluster. Cells may vary in radius from {{convert|1|to|30|km}}. The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells.<ref>J. E. Flood. Telecommunication Networks. Institution of Electrical Engineers, London, UK, 1997. chapter 12.</ref>

The frequency reuse factor is the rate at which the same frequency can be used in the network. It is ''1/K'' (or ''K'' according to some books) where ''K'' is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12, depending on notation).<ref>{{cite web|url=http://www.thereversephone.com/phone-networks/phone-networks/|title=Phone Networks|date=8 June 2011|publisher=The Reverse Phone|access-date=2 April 2012|archive-url=https://web.archive.org/web/20120430205327/http://www.thereversephone.com/phone-networks/phone-networks/|archive-date=30 April 2012|url-status=dead|df=dmy-all}}</ref>

In case of ''N'' sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. ''N'' is typically 3. A '''reuse pattern''' of ''N/K'' denotes a further division in frequency among ''N'' sector antennas per site. Some current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 ([[GSM]]).

If the total available [[bandwidth (signal processing)|bandwidth]] is ''B'', each cell can only use a number of frequency channels corresponding to a bandwidth of ''B/K'', and each sector can use a bandwidth of ''B/NK''.

[[Code-division multiple access]]-based systems use a wider frequency band to achieve the same rate of transmission as FDMA, but this is compensated for by the ability to use a frequency reuse factor of 1, for example using a reuse pattern of 1/1. In other words, adjacent base station sites use the same frequencies, and the different base stations and users are separated by codes rather than frequencies. While ''N'' is shown as 1 in this example, that does not mean the CDMA cell has only one sector, but rather that the entire cell bandwidth is also available to each sector individually.

Recently also [[orthogonal frequency-division multiple access]] based systems such as [[3GPP Long Term Evolution|LTE]] are being deployed with a frequency reuse of 1. Since such systems do not spread the signal across the frequency band, 
inter-cell radio resource management is important to coordinate resource allocation between different cell sites and to limit the inter-cell interference. There are various means of [[inter-cell interference coordination]] (ICIC) already defined in the standard.<ref>{{cite web|url=http://www.nomor.de/uploads/a4/81/a4815c4dc585be33c81f0ec7a15deed7/2010-12-WhitePaper_LTE_HetNet_ICIC.pdf|title=Heterogeneous LTE Networks and Inter-Cell Interference Coordination|last=Pauli|first=Volker|author2=Naranjo, Juan Diego|author3=Seidel, Eiko|date=December 2010|publisher=Nomor Research|access-date=2 April 2012|archive-url=https://web.archive.org/web/20130903122150/http://www.nomor.de/uploads/a4/81/a4815c4dc585be33c81f0ec7a15deed7/2010-12-WhitePaper_LTE_HetNet_ICIC.pdf|archive-date=3 September 2013|url-status=dead|df=dmy-all}}</ref> Coordinated scheduling, multi-site MIMO or multi-site beamforming are other examples for inter-cell radio resource management that might be standardized in the future.