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 λP, λD and λN, 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(λP, λD, λN). 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). © 2015 IEEE.