Limited Feedback MU-MIMO-OFDM Systems

Practical precoding schemes inevitably have to deal with the problem of imperfect, rather than ideal, channel state information at the transmitter (CSIT). This impairment permeates all the processing steps conducted at the transmitter side and it also conditions the receiver design. This paper tackles the problem of designing multiuser MIMO-OFDM (MU-MIMO-OFDM) schemes when only limited feedback is available, with a particular emphasis on the case of IEEE 802.11ac. After deriving a statistical model for the interference caused by limited-feedback valid for various linear precoding schemes, it is shown how this information can be incorporated to the processes of user selection and link adaptation in the context of IEEE 802.11ac. Extensive simulation results are presented assessing the performance of the various limited-feedback designs and comparing them with their perfect CSIT counterparts.