Editing Cellular network (section)

== Directional antennas ==
[[File:CellTowersAtCorners.gif|thumb|382px|Cellular telephone frequency reuse pattern. See {{US patent|4,144,411}}]]

Cell towers frequently use a [[Directional antenna|directional signal]] to improve reception in higher-traffic areas. In the [[United States]], the [[Federal Communications Commission]] (FCC) limits omnidirectional cell tower signals to 100 watts of power. If the tower has directional antennas, the FCC allows the cell operator to emit up to 500 watts of [[effective radiated power]] (ERP).<ref name=Drucker>{{Citation
| title = The Myth of Cellular Tower Health Hazards
| url = http://www.wirelessweek.com/news/2007/03/myth-cellular-tower-health-hazards
| author = Drucker, Elliott
| access-date = 19 November 2013
| archive-url = https://web.archive.org/web/20140502012734/http://www.wirelessweek.com/news/2007/03/myth-cellular-tower-health-hazards
| archive-date = 2 May 2014
| url-status = dead
}}</ref>

Although the original cell towers created an even, omnidirectional signal, were at the centers of the cells and were omnidirectional, a cellular map can be redrawn with the cellular telephone towers located at the corners of the hexagons where three cells converge.<ref>{{cite web|url=http://www.privateline.com/Cellbasics/Cellbasics02.html|title=Cellular Telephone Basics|date=1 January 2006|publisher=Privateline.com|page=2|access-date=2 April 2012|url-status=dead|archive-url=https://web.archive.org/web/20120417220750/http://www.privateline.com/Cellbasics/Cellbasics02.html|archive-date=17 April 2012}}</ref>  Each tower has three sets of directional antennas aimed in three different directions with 120 degrees for each cell (totaling 360 degrees) and receiving/transmitting into three different cells at different frequencies. This provides a minimum of three channels, and three towers for each cell and greatly increases the chances of receiving a usable signal from at least one direction.

The numbers in the illustration are channel numbers, which repeat every 3 cells. Large cells can be subdivided into smaller cells for high volume areas.<ref>{{US patent|4144411}} – ''Cellular Radiotelephone System for Different Cell Sizes'' – Richard H. Frenkiel (Bell Labs), filed 22 September 1976, issued 13 March 1979</ref>

Cell phone companies also use this directional signal to improve reception along highways and inside buildings like stadiums and arenas.<ref name="Drucker"/>