Achievable sum DoF of the K-user MIMO interference channel with delayed CSIT

Abstract

This paper considers a K-user multiple-inputmultiple-output (MIMO) interference channel (IC) where 1) the channel state information obtained by the transmitters (CSIT) is completely outdated, and 2) the number of transmit antennas at each transmitter, i.e., M, is greater than the number of receive antennas at each user, i.e., N. The usefulness of the delayed CSIT was firstly identified in a K-phase Retrospective Interference Alignment (RIA) scheme proposed by Maddah-Ali et al for the Multiple-Input-Single-Output Broadcast Channel, but the extension to the MIMO IC is a non-trivial step as each transmitter only has the message intended for the corresponding user. Recently, Abdoli et al focused on a Single-Input-SingleOutput IC and solved such bottleneck by inventing a K-phase RIA with distributed overheard interference retransmission. In this paper, we propose two K-phase RIA schemes suitable for the MIMO IC by generalizing and integrating some key features of both Abdoli’s and Maddah-Ali’s works. The two schemes jointly yield the best known sum Degrees-of-Freedom (DoF) performance so far. For the case M N ≥K, the achieved sum DoF is asymptotically given by 64 15N when K→∞.