Degrees-of-Freedom of the K-User MISO Interference Channel with Delayed Local CSIT

Abstract: This paper considers a K-user Multiple-Input-Single-Output (MISO) Interference Channel (IC), where the channel state information obtained by the transmitters (CSIT) is perfect, but completely outdated. A Retrospective Interference Alignment (RIA) using such delayed CSIT was proposed by the authors of [1] for the MISO Broadcast Channel (BC), but the extension to the MISO IC is a non-trivial step as each transmitter only has the message intended for the corresponding user. Recently, [7] focused on a Single-Input-Single-Output (SISO) IC and solved such bottleneck by inventing a distributed higher order symbol generation. Our main work is to extend [7] to the MISO case by integrating some features of the scheme proposed in [1]. The achieved sum Degrees-of-Freedom (DoF) performance is asymptotically given by 64/15 when $K\to\infty$, outperforming all the previously known results.