Degrees of Freedom of $M\times N$ SISO X Channel with Synergistic   Alternating CSIT
  In this paper, degrees of freedom (DoF) is investigated for the $M\times N$ single input single output (SISO) X channel with alternating channel state information at the transmitters (CSIT). It is known that the 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]. In this paper, such 2-user X channel schemes are extended to the general $M\times N$ X channel. It is shown that the proposed $M\times N$ X channel schemes with synergistic alternating CSIT achieve $2M/(M+1)$ sum DoF. This DoF with $M=N=K$ is strictly lager than the best known DoF for the $K$-user X channel with delayed CSIT. 
Young-Sik Moon (Department of Electrical and Computer Engineering,   INMC, Seoul National University), Jae-Hong Kim (Samsung...
cs.IT math.IT