Optimization Transmission for Improving Degrees of Freedom in MIMO Y Channel

In this paper, we consider K-user multiple input and multiple output (MIMO) Y channel where each user is equipped with M antennas and the relay N antennas. A scheme that each user exchanges d pairs of messages with each of the other users simultaneously via an intermediate relay is proposed. It is accomplished by utilizing signal space alignment for network coding and interference nulling beam forming combined with receiving antenna selection technique. By using multiple antennas at both ends of wireless links, more diversity gain can be obtained if d is small, while more degrees of freedom (DOF) can be achieved if d becomes larger. The feasibility conditions and the achievable DOF are verified at last.