From the figure, we observe that the performance

gap between ideal and realistic feedback

is much more pronounced for MU-MIMO compared

to SU-MIMO, which illustrates the

increased sensitivity of MU-MIMO with respect

to CSI accuracy. This is due to the fact that

more accurate CSI feedback helps to improve

the accuracy with which interference nulling can

be performed at the eNB and to better predict

the MU-CQIs, which are crucial for multi-user

scheduling [7]. While Fig. 1 sheds light on the

benefits that may be achieved with improved

CSI feedback accuracy, in practice a tradeoff

between improving downlink performance and

increasing uplink overhead needs to be struck.

In Rel-10, increasing the granularity of the feedback

codebooks was discussed but no agreement