Frequency–division duplexing (FDD) is a method for establishing a full-duplex communications link that uses two different radio frequencies for transmitter and receiver operation. The transmit direction and receive direction frequencies are separated by a defined frequency offset.
Duplexing is the process of achieving two-way communications over a communications channel. It takes two forms: half duplex and full duplex.
Duplex is of two types
Full and Half Duplex.
In half double, the couple communicating parties diversify transmitting over a mutual convey. Two-way radios work this way. As tyrannical talks, the separate listens. Speaking parties regularly say “Over” to argue that they’re lost and it’s time for the separate team to utter. In networking, a sole cable is communal as the pair computers communicating range dispatching and inheriting data.
Full duplex refers to simultaneous two-way communications. The two communicating stations can send and receive at the same time. Landline telephones and cell phones work this way. Some forms of networking permit simultaneous transmit and receive operations to occur.
This is the more desirable form of duplexing, but it is more complex and expensive than half duplexing. There are two basic forms of full duplexing: frequency division duplex (FDD) and time division duplex (TDD).
Because the FDD technique uses different frequency bands for send and receive operations, the sending and receiving data signals don’t interfere with each other. This makes FDD a better choice than Time Division Duplex (TDD) for symmetric traffic such as voice applications in broadband wireless networks.
Most cell-phone systems use FDD. The newer LTE and 4G systems use FDD. Cable TV systems are fully FDD.
Most wireless data transmissions are TDD. WiMAX and Wi-Fi use TDD. So does Bluetooth when piconets are deployed. ZigBee is TDD. Most digital cordless telephones use TDD. Because of the spectrum shortage and expense, TDD is also being adopted in some cellular systems, such as China’s TD-SCDMA and TD-LTE systems. Other TD-LTE cellular systems are expected to be deployed where spectrum shortages occur.
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