On the degrees of freedom of SISO interference and X channels with delayed CSIT

Abstract

The SISO (single-input single-output) AWGN interference and X channels in i.i.d. fading environment are considered where the transmitters have the past channel state information (CSI) through noiseless feedback links. New transmission schemes are proposed for these channels that achieve degrees of freedom (DoF) values greater than one (except for two-user interference channel). The achieved DoFs are strictly increasing with the number of users and asymptotically approach limiting values of ≈ 1.2663 and ≈ 1.4427 for interference and X channels, respectively. The achieved DoFs are greater than the best previously reported DoFs for these channels with delayed CSI at transmitters.