Retrospective Network Coding Alignment Over $K$-User MIMO Y Channel

Under the assumption that each node has delayed channel state information at transmitter (D-CSIT), this letter studies the achievable degrees of freedom (DOF) for K-user multiple-input-multiple-output (MIMO) Y channel in frequency division duplex (FDD) systems, where each user exchanges messages with other K-1 users simultaneously via an intermediate relay. We propose a new retrospective network coding alignment (RNCA) scheme and derive the closed-form expression for achievable DOF.