Editing Duplex (telecommunications) (section)

=== Frequency-division duplexing === <!--[[Frequency-division duplex]] and others link here-->
{{confused|Frequency-division multiplexing}}
'''Frequency-division duplexing''' ('''FDD''') means that the [[transmitter]] and [[receiver (radio)|receiver]] operate using different [[carrier frequencies]]. 

The method is frequently used in [[ham radio]] operation, where an operator is attempting to use a [[repeater]] station. The repeater station must be able to send and receive a transmission at the same time and does so by slightly altering the frequency at which it sends and receives.  This mode of operation is referred to as ''duplex mode'' or ''offset mode''. Uplink and downlink sub-bands are said to be separated by the ''frequency offset''. 

Frequency-division duplex systems can extend their range by using sets of simple repeater stations because the communications transmitted on any single frequency always travel in the same direction.

Frequency-division duplexing can be efficient in the case of symmetric traffic. In this case, time-division duplexing tends to waste bandwidth during the switch-over from transmitting to receiving, has greater inherent [[Latency (engineering)|latency]], and may require more complex [[circuitry]].

Another advantage of frequency-division duplexing is that it makes radio planning easier and more efficient since base stations do not ''hear'' each other (as they transmit and receive in different sub-bands) and therefore will normally not interfere with each other. Conversely, with time-division duplexing systems, care must be taken to keep guard times between neighboring base stations (which decreases [[spectral efficiency]]) or to synchronize base stations, so that they will transmit and receive at the same time (which increases network complexity and therefore cost, and reduces bandwidth allocation flexibility as all base stations and sectors will be forced to use the same uplink/downlink ratio).

Examples of frequency-division duplexing systems include:
* [[ADSL]] and [[VDSL]]
* [[Mobile technology]], including [[LTE (telecommunication)|LTE]], [[UMTS]] and [[CDMA2000]]
* [[IEEE 802.16]] [[WiMax]]