DoF achieving backward transmission of reciprocal propagation delay based X channels with two transmitters

Abstract

This letter proposes an optimal scheme for the backward transmission of the propagation-delay (PD) based X channels with two transmitters and arbitrary receivers, which has reciprocal PD channel of the given forward transmission. Cyclic interference alignment is used to maximize the degrees of freedom (DoF), where the interference messages are shown to be aligned into one time-slot. This work helps support optimal bidirectional transmission of the discussed X channels.