FDD

Frequency Division Duplex is a technology used in wireless communications where the uplink and the downlink use a different frequency. The uplink and downlink are separated by a certain gap. This is called the duplex distance or duplex spacing.

FDD can be used for simultanious transmission and reception (full duplex). However, FDD is very inefficient if the traffic pattern is asymmetric because the bandwidth of the two associated frequency channels are fixed.