The LTE standard specifies two different duplex modes; FDD and TDD. In Frequency Division Multiplex (FDD) mode the uplink and downlink are using separate frequencies. In Time Division Multiplex (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 HW platforms for eNode B 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:
- TDD has a 3 to 6 dB weaker link budget compared to FDD, depending on UL:DL allocation
- LTE TDD requires high accuracy synchronization within the network and also towards other TDD systems for efficient co-existence
- LTE TDD has potentially more flexibility in applying beamforming schemes (due to thefact that eNode B has more knowledge on channel conditions in absence of UE report)
TD-LTE, FD-LTE, FDD-LTE,TDD-LTE
