Editing Time-division multiple access (section)

{{Short description|Channel access method for networks using a shared communications medium}}
{{About|the channel access method|the obsolete U.S. mobile-telephone standard that uses TDMA to control channel access|Digital AMPS}}
{{more citations needed|date=August 2011}}

[[Image:Tdma-frame-structure.png|thumbnail|350px|TDMA frame structure showing a data stream divided into frames and those frames divided into time slots]]

'''Time-division multiple access''' ('''TDMA''') is a [[channel access method]] for [[shared-medium network]]s. It allows several users to share the same [[frequency channel]] by dividing the signal into different time slots.<ref name=Zander>{{cite book|author1=Guowang Miao|author-link=Guowang Miao|author2=Jens Zander|author3=Ki Won Sung|author4=Ben Slimane|title=Fundamentals of Mobile Data Networks|publisher=[[Cambridge University Press]]|isbn=978-1107143210|year=2016}}</ref> The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its [[channel capacity]]. '''Dynamic TDMA''' is a TDMA variant that dynamically reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic demand of each data stream.

TDMA is used in digital [[2G]] [[cellular communication networks|cellular systems]] such as [[Global System for Mobile Communications]] (GSM), [[IS-136]], [[Personal Digital Cellular]] (PDC) and [[iDEN]], in the Maritime [[Automatic Identification System]],<ref>{{cite web|title=USCG How IAS Works|url=https://www.navcen.uscg.gov/how-ais-works |website=How IAS Works|access-date=10 March 2025}}</ref> and in the [[Digital Enhanced Cordless Telecommunications]] (DECT) standard for [[portable phone]]s. TDMA was first used in [[satellite communication]] systems by [[Western Union]] in its [[Westar 3]] communications satellite in 1979. It is now used extensively in satellite communications,<ref>{{cite conference|last1=Maine|first1=K.|last2=Devieux|first2=C.|last3=Swan|first3=P.|date=November 1995|url=https://www.researchgate.net/publication/3622510|title=Overview of IRIDIUM satellite network|conference=WESCON'95|page=483|publisher=IEEE}}</ref><ref>{{cite conference|last1=Mazzella|first1=M.|last2=Cohen|first2=M.|last3=Rouffet|first3=D.|last4=Louie|first4=M.|last5=Gilhousen|first5=K. S.|date=April 1993|title=Multiple access techniques and spectrum utilisation of the GLOBALSTAR mobile satellite system|conference=Fourth IEE Conference on Telecommunications 1993|pages=306–311|publisher=IET}}</ref><ref>{{cite conference|last=Sturza|first=M. A.|date=June 1995|url=https://www.researchgate.net/publication/4672931|title=Architecture of the TELEDESIC satellite system|conference=International Mobile Satellite Conference|volume=95|page=214}}</ref><ref>{{cite web|url=https://www.ctu.cz/sites/default/files/cs/download/oznamene_typy_rozhrani/orbcomm-rozhrani_02_06_2010.pdf|title=ORBCOMM System Overview}}</ref> [[combat-net radio]] systems, and [[passive optical network]] (PON) networks for upstream traffic from premises to the operator.

TDMA is a type of [[time-division multiplexing]] (TDM), with the special point that instead of having one [[transmitter]] connected to one [[Receiver (radio)|receiver]], there are multiple transmitters. In the case of the ''[[uplink]]'' from a [[mobile phone]] to a [[base station]] this becomes particularly difficult because the mobile phone can move around and vary the ''timing advance'' required to make its transmission match the gap in transmission from its peers.