Difference in between LTE FDD and TDD?

What is difference in between LTE FDD & TDD?

In both LTE FDD and LTE TDD, the transmitted signal is organized into subframes of 1 millisecond (ms) duration and 10 subframes constitute a radio frame. Each subframe normally consists of 14 OFDM symbols (12 OFDM symbols in case of the so-called Extended Cyclic Prefi).

Although the frame structure is, in most respects, the same for LTE FDD and LTE TDD, there are some differences between the two, most notably the use of special subframes in TDD. Another difference is the other subframes are allocated either for uplink transmission or for downlink transmission.

In case of FDD operation, there are two carrier frequencies, one for uplink transmission (fUL) and one for downlink transmission (fDL). During each frame, there are consequently 10 uplink subframes and 10 downlink subframes and uplink and downlink transmission can occur simultaneously within a cell.

In case of TDD operation, there is only one single carrier frequency and uplink and downlink transmissions in the cell are always separated in time. As the same carrier frequency is used for uplink and downlink transmission, both the base station and the mobile terminals must switch from transmission to reception and vice versa. Thus, as a subframe is either an uplink subframe or a downlink subframe, the number of subframes per radio frame in each direction is less than 10.

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