Multiuser MIMO Downlink: Multiplexing Gain Without Free Channel Information

Abstract

A multiuser MIMO system is considered with no initial assumption of channel state information (CSI) at any of the receivers or the BS transmitter. For a system working under frequency-division duplexing (FDD) mode, simple practically realizable transmission strategy is proposed which provides necessary channel state information to both sides with minimal resource utilization for downlink (DL) data transmission. For the given transmission strategy, high SNR degrees of freedom (DOF) for the DL channel are specified. If the users have data to transmit in the uplink (UL) direction, with no extra burden of training, full multiplexing gain of the multiple-access channel (MAC) can be achieved. Thus the given strategy makes the system fully scalable for the data transmission in both directions.