Degrees of Freedom of M N SISO X Channel with Synergistic Alternating CSIT

In this paper, we investigate degrees of freedom (DoF)of the M N single input single output (SISO) X channel withalternating channel state information at the transmitter (CSIT). Itis known that sum DoF of 2-user SISO X channel with synergisticalternating CSIT is the same as the sum DoF of 2-user (M = N =2) SISO X channel with perfect CSIT [8]. As an extension of the2-user case, achievable schemes of the M N SISO X channelwith synergistic alternating CSIT are proposed. It is shown that theproposed M N X channel schemes with synergistic alternatingCSIT achieve the sum DoF 2M=(M +1), which is better than theweighted sum DoF of the conventional schemes for M N. TheDoF of the proposed scheme with M = N = K is strictly betterthan the best known DoF for the K-user X channel with delayedCSIT.