LTE standard specifies two different duplex modes; Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD). In FDD mode the uplink and downlink are using separate frequencies. In TDD mode the uplink and downlink use the same frequency but are separated in time.
These two modes have been harmonized in 3GPP to a large extent enabling vendors to use same Hardware platforms for eNodeBs and to develop terminals supporting both modes of operation.
Due to the commonalities between LTE FDD & TDD modes, their performance is similar in many aspects, such as spectrum efficiency. The fundamental characteristics of FDD and TDD however also lead to differences:
Major Differences between TDD and FDD