Editing Space-division multiple access (section)

{{Short description|Channel-access method in communications}}
{{Use American English|date = March 2019}}
{{Other uses|Space Division (disambiguation){{!}}Space Division}}
{{refimprove|date=July 2016}}
{{Multiplex techniques}}
'''Space-division multiple access''' ('''SDMA''') is a [[channel access method]] based on creating parallel spatial pipes (focused signal beams) using advanced antenna technology next to higher capacity pipes through spatial multiplexing and/or diversity, by which it is able to offer superior performance in radio multiple access communication systems (where multiple users may need to use the communication media simultaneously).<ref>{{Cite web|url=https://www.techopedia.com/definition/2979/spatial-division-multiple-access-sdma|title=What is Spatial Division Multiple Access (SDMA)? - Definition from Techopedia|website=Techopedia.com|language=en|access-date=2019-11-20}}</ref> In traditional mobile [[cellular network]] systems, the [[base station]] has no information on the position of the mobile units within the cell and radiates the signal in all directions within the cell in order to provide radio coverage. This method results in wasting power on transmissions when there are no mobile units to reach, in addition to causing [[co-channel interference|interference]] for adjacent cells using the same frequency (so-called [[co-channel]] cells). Likewise, in reception, the [[Antenna (radio)|antenna]] receives signals coming from all directions including noise and interference signals. By using [[smart antenna]] technology and differing spatial locations of mobile units within the cell, space-division multiple access techniques offer attractive performance enhancements. The [[radiation pattern]] of the base station, both in transmission and reception, is adapted to each user to obtain highest gain in the direction of that user. This is often done using [[phased array]] techniques.