Linear degrees of freedom of two-user MIMO broadcast channels with reconfigurable antennas in the absence of CSIT

The degrees of freedom (DoF) of the two-user multiple-input and multiple-output (MIMO) broadcast channel (BC) without channel state information at the transmitter (CSIT) is studied, in which each receiver is equipped with reconfigurable antennas capable of choosing a subset of receiving modes from several preset modes. Under a general setting of arbitrary number of transmit antennas, receiving modes, and preset modes, the linear sum DoF is completely characterized by developing an optimal blind interference alignment scheme and obtaining a matching upper bound available for any linear coding strategy.