Editing Time-division multiple access (section)

== Comparison with other multiple-access schemes ==
In radio systems, TDMA is usually used alongside [[frequency-division multiple access]] (FDMA) and frequency-division duplex (FDD); the combination is referred to as FDMA/TDMA/FDD. This is the case in both GSM and IS-136 for example. Exceptions to this include the [[DECT]] and [[Personal Handy-phone System]] (PHS) micro-cellular systems, [[UMTS-TDD]] UMTS variant, and China's [[TD-SCDMA]], which use time-division duplexing, where different time slots are allocated for the base station and handsets on the same frequency.

A major advantage of TDMA is that the radio part of the mobile-only needs to listen and broadcast for its own time slot. For the rest of the time, the mobile can carry out measurements on the network, detecting surrounding transmitters on different frequencies. This allows safe inter-frequency [[handover]]s, something which is difficult in CDMA systems, not supported at all in [[IS-95]] and supported through complex system additions in [[Universal Mobile Telecommunications System]] (UMTS). This in turn allows for co-existence of [[microcell]] layers with [[macrocell]] layers.

CDMA, by comparison, supports "soft hand-off" which allows a mobile phone to be in communication with up to 6 base stations simultaneously, a type of "same-frequency handover". The incoming packets are compared for quality, and the best one is selected. CDMA's "cell breathing" characteristic, where a terminal on the boundary of two congested cells will be unable to receive a clear signal, can often negate this advantage during peak periods.

A disadvantage of TDMA systems is that they create [[electromagnetic interference|interference]] at a frequency that is directly connected to the time slot length. This is the buzz that can sometimes be heard if a TDMA phone is left next to a radio or speakers.<ref>{{cite web | url=http://www.eetimes.com/design/microwave-rf-design/4019057/Minimize-GSM-buzz-noise-in-mobile-phones | title=Minimize GSM buzz noise in mobile phones | publisher = EETimes | date=July 20, 2009 | access-date=November 22, 2010}}</ref>  Another disadvantage is that the "dead time" between time slots limits the potential bandwidth of a TDMA channel. These are implemented in part because of the difficulty in ensuring that different terminals transmit at exactly the times required. Handsets that are moving will need to constantly adjust their timings to ensure their transmission is received at precisely the right time because as they move further from the base station, their signal will take longer to arrive. This also means that the major TDMA systems have hard limits on cell sizes in terms of range, though in practice the power levels required to receive and transmit over distances greater than the supported range would be mostly impractical anyway.