The Degrees-of-Freedom of Multi-way Device-to-Device Communications is Limited by 2

TL;DR

This paper investigates the degrees-of-freedom in a 3-user device-to-device communication scenario, establishing an approximate capacity limit and revealing analogies with relay communications.

Contribution

It derives a sum-capacity upper bound for the 3-way D2D channel and shows this bound is achievable within 2 bits, providing an approximate capacity characterization.

Findings

Sum-capacity upper bound derived using genie-aided arguments.

Achievability within 2 bits of the upper bound.

Analogies between multi-way D2D and relay communications identified.

Abstract

A 3-user device-to-device (D2D) communications scenario is studied where each user wants to send and receive a message from each other user. This scenario resembles a 3-way communication channel. The capacity of this channel is unknown in general. In this paper, a sum-capacity upper bound that characterizes the degrees-of-freedom of the channel is derived by using genie-aided arguments. It is further shown that the derived upper bound is achievable within a gap of 2 bits, thus leading to an approximate sum-capacity characterization for the 3-way channel. As a by-product, interesting analogies between multi-way communications and multi-way relay communications are concluded.