Interference aligned space-time transmission with diversity for the 2 × 2 X-Network

It is well known that the interference alignment (IA) based transmission scheme proposed by Jafar and Shamai achieves the 4M over 3 sum-degrees of freedom (DoF) of the twotransmitter, two-receiver multiple-input multiple-output (MIMO) X-Network with M antennas at each node, referred to as the (2 × 2, M) X-Network. The Jafar-Shamai scheme assumes the availability of “global” channel-state-information at the transmitter (CSIT). “Local” CSIT based transmission schemes that couple IA with space-time block codes (STBC) in order to achieve the sum-DoF of the (2 × 2, M) X-Network are known specifically for M = 2; 3; 4. Further, these schemes have been proven to guarantee a diversity gain of M when finite-sized input constellations are employed. In this paper, an explicit transmission scheme that achieves the 4M over 3 sum-DoF of the (2 × 2, M) X-Network, for arbitrary M, is presented. The proposed scheme needs only local CSIT unlike the Jafar-Shamai scheme. In addition, it is shown analytically that the proposed scheme guarantees a diversity gain of M + 1 when finite-sized input constellations are employed.