1.3 Duplex Techniques
1.3.1 Time Division Duplex [TDD]
Using the TDD method, a single frequency channel is assigned to both the
transmitter and the receiver. Both the uplink (UL) and downlink (DL) traffic use
the same frequency f0 but at different times.
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.
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
• 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.
1.3.1 Time Division Duplex [TDD]
Using the TDD method, a single frequency channel is assigned to both the
transmitter and the receiver. Both the uplink (UL) and downlink (DL) traffic use
the same frequency f0 but at different times.
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.
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
• 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.
