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 trans-mission 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 ps 1.2663 and m 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.