9.9 Summary

The cell search design in LTE supports scalable bandwidths with a minimum bandwidth of 1.08 MHz. The synchronization signals and broadcast control information are transmitted in the center 1.08 MHz bandwidth irrespective of the system bandwidth. This allows UEs to acquire time and frequency synchronization with the network without knowledge of the system bandwidth, which makes the cell search more efficient and faster. After achieving the timing and frequency synchronization, the UE can obtain the remaining cell/systemspecific information from the broadcast control channel. The information on the eNB antenna configuration is also encoded in the cyclic redundancy check on the broadcast control channel. Therefore, after successful reception of the broadcast control and CRC check, the UE also acquires information on the number of antenna ports supported by the eNB.

Three types of reference signals namely cell-specific reference signal, MBSFN reference signals and UE-specific reference signals are defined for the downlink. All the reference signals are multiplexed with data within a subframe using a hybrid TDM / FDM approach. In this hybrid TDM / FDM approach, a fraction of the subcarriers in a few OFDM symbols within a subframe is used for reference signals transmission. The number of cell-specific reference signals equals the number of antenna ports supported by the eNB. On the other hand, both UE-specific and MBSFN reference signals are defined with a single port which means that only rank-1 transmissions can be performed for MBSFN and for UEs scheduled using UE-specific reference signals.

The cell-specific...