ysical Downlink Shared Channel (PDSCH), as shown in Figure 2.2. With the Time-Division Duplex (TDD) operation, there are some differences in the frame structure as shown in Figure 2.2. There is the special sub-frame when the trans- mission direction changes between uplink and downlink. In the first versions of TDD LTE and LTE Advanced in Releases 8-11 12 or 14 OFDM symbols Single PRB Total System Bandwidth Sub-carriers for the 1.4-20 MHz First Symbol in a Single Resource Block 180 kHz = 12 sub-carriers 1 ms sub-frame (allocation period) Resource Blocks for a single UE Figure 2.1 Downlink 1 ms allocation structure (TD-LTE), the uplink/downlink configuration is static parameter, which also allows prevent- ing uplink/downlink interference between different cells. The more dynamic allocation of resources is addressed in Release 12 as discussed in Chapter 4. The TDD cells can be param- eterized based on the average traffic asymmetry by choosing the suitable uplink/downlink configuration. In the structure in Figure 2.3, the first sub-frame is always allocated for down- link direction while the first sub-frame after the special sub-frame is allocated for the uplink direction. After that the chosen configuration determines when downlink allocation starts Control Symbols = PDCCH Data Symbols = PDSCH Sub-carriers 1 ms sub-frame 0.5 ms slot 10 ms frame Figure 2.2 Downlink frame structure LTE Small Cell Optimization Downlink Uplink Uplink or downlink Special sub-frame 1 ms sub-frame DwPTS UpPTS 0.5 ms slot One half-frame (5 ms) 10 ms frame Figure 2.3 LTE TDD frame structure again. The use of maximum asymmetry to boost downlink capacity needs to be done with care as then the resulting uplink capacity and especially range are respectively more limited if a UE with power limitation at cell edge can only transmit once per 10 ms frame. In general, 3GPP has minimized the differences between feature-driven development (FDD) and TDD to facilitate easy implementation of both eNodeBs and UEs that may support both modes of operation. T