Duplexing methods are used in dividing forward and reverse communication channels in communication mediums. There are three major types of duplexing methods in wireless communication channels; Time Division duplexing (TDD) and Frequency Division Duplexing (FDD). Other duplexing methods can include Echo cancellation.

In FDD, systems can do simultaneous transmission and reception because the downlink (receive) frequencies are separate from the uplink (transmit) frequencies). FDD systems use filters for a radio with a receiver and transmitter to filter out noises from either receiver or transmitter. Guard bands are used to make the filters effective by separating downlink and uplink frequencies.
Click image for larger version Name: FDD.jpg Views: 28 Size: 16.8 KB ID: 2755



Use cases of FDD:
  • Microwave links
  • mmWave links
  • Most 4G/LTE networks (some use TDD)

Check out these external filters that can be used in RF systems to allow or block certain frequencies in the system.

TDD systems cannot do simultaneous transmission and reception. In TDD, a certain time slot is set for RX for DL/receive and a certain time slot is reserved for UL/transmit. The system rapidly switches between transmit and receive. The systems in TDD can be asymmetrical as required to accommodate either more download or upload.
TDD also uses guard times to prevent overlap between downlinks and uplinks.
Click image for larger version Name: TDD.jpg Views: 9 Size: 14.5 KB ID: 2756



Use cases of TDD:
  • Wi-Fi networks
  • Some 4G/LTE networks

Check out these amplifiers that can be used in FDD and TDD systems.

Contact an Rfwel Engineering Wireless Specialist to learn more about RF equipment that you can use in your RF system implementation.