Abstract : In this paper, we investigate degrees of freedom (DoF) of theM×NM×Nsingle input single output (SISO) X channel with alternating channel state information at the transmitter (CSIT). It is known that sum DoF of 2-user SISO X channel with synergistic alternating 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 the 2-user case, achievable schemes of theM×NM×NSISO X channel with synergistic alternating CSIT are proposed. It is shown that the proposedM×NM×NX channel schemes with synergistic alternating CSIT achieve the sum DoF 2M/(M +1), which is better than the weighted sum DoF of the conventional schemes forM≤NM≤N. The DoF of the proposed scheme with M = N = K is strictly better than the best known DoF for the K-user X channel with delayed CSIT.
Index terms : Channel state information at the transmitter (CSIT), degrees of freedom (DoF), interference alignment, single input single output (SISO) X channel