Degrees of Freedom of $M\times N$ SISO X Channel with Synergistic Alternating CSIT

TL;DR

This paper extends the understanding of degrees of freedom in MxN SISO X channels with alternating CSIT, proposing schemes that achieve higher DoF than previous delayed CSIT methods.

Contribution

It introduces new transmission schemes for MxN SISO X channels with synergistic alternating CSIT, achieving improved sum DoF over existing delayed CSIT approaches.

Findings

Achieves sum DoF of 2M/(M+1) for MxN SISO X channels.

Shows the proposed schemes outperform delayed CSIT methods.

Extends 2-user X channel results to general MxN cases.

Abstract

In this paper, degrees of freedom (DoF) is investigated for the $M\times N$ single input single output (SISO) X channel with alternating channel state information at the transmitters (CSIT). It is known that the sum DoF of 2-user SISO X channel with synergistic alternating CSIT is the same as the sum DoF of 2-user $(M=N=2)$ SISO X channel with perfect CSIT [8]. In this paper, such 2-user X channel schemes are extended to the general $M\times N$ X channel. It is shown that the proposed $M\times N$ X channel schemes with synergistic alternating CSIT achieve $2M/(M+1)$ sum DoF. This DoF with $M=N=K$ is strictly lager than the best known DoF for the $K$-user X channel with delayed CSIT.