Evolved Packet System (EPS): The LTE and SAE Evolution of 3G UMTS

3.6 FDD and TDD Arrangement for E-UTRAN

Part of the requirements for ‘evolved UTRAN’ is the ability to cope with various spectrum allocations from much less than 5 MHz to much more than 5 MHz, accommodating future 3G spectrum allocations. Ultimately, the maximum achievable data rate available should be 100 Mb/s in 20 MHz. Multicarrier technology should then allow a smooth migration from 1.25-MHz bandwidth to 20-MHz through 5, 10 and 15-MHz steps.

Figure 3.35 Possible TDD/FDD modes and interactions.

To increase this flexibility, the E-UTRAN air interface supports both frequency division duplex (FDD) and time division duplex (TDD) modes of operation (Figure 3.35). Moreover, most of the design parameters are common to TDD and FDD modes to reduce the complexity of the terminal.

3.6.1 A Word about Interferences in TDD Mode

TDD mode often requires synchronization between various transmitters and receivers in different cells. The reason why is discussed in the following and can easily be understood when looking at Figure 3.36. Two problem cases can be observed, in which either:

• Two non-synchronized close UEs (User Equipments – the 3GPP term for mobile terminal) jam each other in a near–far context. The strong signal from the UE1-TX (transmitter) destined to far station 1 RX (receiver) can jam the close UE2-RX if the TX-UE1/RX-UE2 ranges overlap.

  Figure 3.36 Interferences in TDD mode. ...