On the synergistic benefits of alternating CSIT for X channel within a four-symbol channel extension

In this paper, we investigate the degrees of freedom (DoF) of the two-user single input single output (SISO) X channel with alternating channel state information at the transmitters (CSIT). Three cases are considered for the availability of CSIT; perfect, delayed and no-CSIT. Each state is associated with a fraction of time denoted by λ<sub>P</sub>, λ<sub>D</sub> and λ<sub>N</sub>, respectively. We provide new results for the achievable DoF of the channel when the available CSIT alternates between these three cases under a certain distribution for Λ(λ<sub>P</sub>, λ<sub>D</sub>, λ<sub>N</sub>). Specifically, we show that the two-user SISO X channel with alternating CSIT for Λ(1/8, 3/8, 1/2) can achieve 5/4 DoF. The achieved DoF in this case lie between the maximum DoF of the channel, i.e., 4/3 DoF for Λ(1, 0, 0), and the 6/5 DoF achieved for Λ(0, 1, 0).

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