Time-division duplex

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Time-Division Duplex (TDD) is the application of time-division multiplexing to separate outward and return signals. It emulates full duplex communication over a half duplex communication link. Time division duplex has a strong advantage in the case where the asymmetry of the uplink and downlink data speed is variable. As the amount of uplink data increases, more bandwidth can dynamically be allocated to that and as it shrinks it can be taken away. Another advantage is that the uplink and downlink radio paths are likely to be very similar in the case of a slow moving system. This means that techniques such as beamforming work well with TDD systems.

[edit] Examples

Examples of TDD systems are:

• The W-CDMA TDD mode (for indoor use)
• UMTS-TDD's TD-CDMA air interface
• The TD-SCDMA system
• DECT
• IEEE 802.16 WiMax TDD mode
• Universal Serial Bus
• Half-duplex packet mode networks based on carrier sense multiple access, for example 2-wire or hubbed Ethernet, Wireless local area networks and Bluetooth, can be considered as TDD systems, albeit not TDMA with fixed frame length.