On the Benefit of Cooperation in Relay Networks

TL;DR

This paper investigates how cooperation facilitated by a rate-limited device can significantly improve network throughput, especially in relay networks, by analyzing conditions for infinite-slope rate benefits at zero cooperation rate.

Contribution

It extends the CF model to relay networks, providing conditions under which cooperation yields infinite-slope benefits similar to MAC encoders.

Findings

Infinite-slope benefits are achievable in relay networks under certain conditions.

Generalization of lower bounds shows when cooperation significantly improves rates.

Identifies network configurations where cooperation benefits are directly linked to MAC properties.

Abstract

This work addresses the cooperation facilitator (CF) model, in which network nodes coordinate through a rate limited communication device. For independent multiple-access channel (MAC) encoders, the CF model is known to show significant rate benefits, even when the rate of cooperation is negligible. Specifically, the benefit in MAC sum-rate, as a function of the cooperation rate $C_{CF}$, sometimes has an infinite slope at $C_{CF}=0$. This work studies the question of whether cooperation through a CF can yield similar infinite-slope benefits when applied to internal network encoders in which dependence among MAC transmitters can be established without the help of the CF. Towards this end, this work studies the CF model when applied to relay nodes of a single-source, single-terminal, diamond network consisting of a broadcast channel followed by a MAC. In the relay channel with orthogonal receiver components, careful generalization of the partial-decode-forward/compress-forward lower bound to the CF model yields sufficient conditions for an infinite-slope benefit. Additional results include derivation of a family of diamond networks for which the infinite-slope rate-benefit derives directly from the properties of the corresponding MAC component when studied in isolation.