TABLE OF CONTENTS The downlink transmissions in the LTE system are scheduled on a subframe basis. A subframe of duration 1 ms consists of two slots each of duration 0.5 ms. A group of 20 slots (10 subframes) forms a radio frame of duration 10 ms as shown in Figure 9.3. A slot further consists of seven or six OFDM symbols for the normal cyclic prefix or extended cyclic prefix cases respectively. In the case of 7.5 kHz subcarrier spacing defined for MBSFN and extended cyclic prefix only, a slot consists of three OFDM symbols. For simplicity, we assume the case of normal cyclic prefix with seven OFDM symbols per slot in Figure 9.3.
The cell-specific reference signals are carried in all downlink subframes. The downlink unicast transmissions can be configured to use one, two or four antenna ports. The reference signals for antenna ports 0 and 1 ( R 0, R 1) are carried in the first and third last OFDM symbol within a slot. The reference signals for antenna ports 2 and 3 ( R 2, R 3) are carried in the second OFDM symbol within a slot. For subframes carrying MBSFN, the reference signals for unicast are present only in the first and second OFDM symbols of the first slot within that subframe. The primary synchronization signal (PSS) and secondary synchronization signal (SSS) are carried in the last and second last OFDM symbols respectively in slot...
