CSI feedback allows downlink transmission

to be adaptively optimized based on the

instantaneous DL channel, so that closedloop

beamforming and adaptive link adaptation

can be enabled to optimize the system

performance. The DL reference signal used

for CSI measurement is different in Rel-8

and Rel-10. In Rel-8, CSI measurement is

based on CRS, which is also used for data

demodulation. In contrast, CSI measurement

in Rel-10 is based on a set of newly introduced

CSI-RS signals, which is low-dutycycle

and low-density, and allows a higher

reuse factor than Rel-8 CRS.