Degrees of freedom of relay-assisted MIMO interfering broadcast channels

This work studies achievable degrees of freedom (DoF) of two-cell two-hop interfering broadcast channels. In the two cells, base stations (BS) equipped with Mi and M₂ antennas intend to communicate with M₁ and M₂ single-antenna users, respectively. The messages sent from each BS are first received by two shared full-duplex multiantenna relays simultaneously in the first hop and then are forwarded to the intended users from the relays in the second hop. We study the achievable DoF of the network with various channel state information (CSI) available at the BSs and the users while the relays have CSI of the two-hop channels. We first consider the scenario when the BSs have the CSI of the first hop and the users have the CSI of the second hop, respectively. A linear scheme with precoding at the BSs and interference neutralization at the relays is designed to achieve the cut-set DoF of M₁ + M₂ if both relays have M₁ + M₂ - 1 antennas. We then consider the scenario when the BSs do not have any CSI but the users have the full CSI of both hops. A relay beamforming scheme is proposed to achieve the DoF of M₁ + M₂ when both relays have M₁ + M₂ - 1 antennas.