Degrees of freedom of MIMO Y channel with three semi-blind users

In this paper, we study the degrees of freedom (DOF)for three-user multiple-input and multiple-output (MIMO) Y channel, where each user equipment (UE) sends two independent messages to the other two UEs while receiving two independent messages from them via a common relay node. We assume each UE is equipped with M antennas and is semi-blind in the sense that no channel state information at the transmitter (CSIT) is available in multiple access (MAC) phase, while the relay is equipped with N = 3M antennas. We consider three scenarios: perfect CSIT, delayed CSIT and no CSIT at the relay in Broadcast (BC) phase. We analyze the DOF of all three scenarios systematically. Particularly, when the relay has perfect CSIT, we propose a new joint physical layer network coding and antenna selection (PLNC-AS) algorithm. Simulation results show that this algorithm can achieve 4.5dB performance gain compared to the existing signal space alignment for network coding (SSA-NC) algorithm.