Duplex transmission is the simultaneous transmission of two information signals that allows simultaneous (or near simultaneous) 2-way communication. The WiMAX system can use frequency division duplex (FDD), time division duplex (TDD) or half frequency division duplex (H-FDD).

FDD is the process of simultaneously allowing the transmission of information in both directions via separate frequency bands. When using FDD, each device transmits on one frequency while listening on a different one.

TDD refers to the process of allowing two way communications between two devices by time-sharing. When using TDD, device 1 transmits while device 2 listens for a short period of time. After the transmission is complete, the devices reverse their role so device 1 becomes a receiver and device 2 becomes a transmitter. The process continually repeats itself so data appears to flow in both directions simultaneously.

H-FDD is a process that allows for two-way communications between two devices through the combination of frequency division and time sharing. When using H-FDD, device 1 transmits on one frequency while the device 2 listens for a short period of time on that frequency. After the transmission is complete, the devices reverse their roles and device 2 transmits on a different frequency and the other device listens for a short period of time on that frequency. The process continually repeats itself so data appears to flow in both directions simultaneously. The use of H-FDD systems allows for the simplification of radio design as the transmitters and receivers in the same unit...