Outage Capacity of the Fading Relay Channel in the Low SNR Regime

TL;DR

This paper analyzes the outage capacity of slow fading relay channels in low SNR conditions, showing that a modified Amplify-Forward protocol outperforms standard methods and achieves optimal capacity without channel knowledge.

Contribution

The paper introduces a Bursty Amplify-Forward protocol that is optimal in low SNR regimes and demonstrates its superiority over traditional Decode-Forward methods.

Findings

Bursty Amplify-Forward achieves outage capacity in low SNR regimes.

Decode-Forward is sub-optimal in this regime.

Outage capacity per unit energy is characterized.

Abstract

In slow fading scenarios, cooperation between nodes can increase the amount of diversity for communication. We study the performance limit in such scenarios by analyzing the outage capacity of slow fading relay channels. Our focus is on the low SNR and low outage probability regime, where the adverse impact of fading is greatest but so are the potential gains from cooperation. We showed that while the standard Amplify-Forward protocol performs very poorly in this regime, a modified version we called the Bursty Amplify-Forward protocol is optimal and achieves the outage capacity of the network. Moreover, this performance can be achieved without a priori channel knowledge at the receivers. In contrast, the Decode-Forward protocol is strictly sub-optimal in this regime. Our results directly yield the outage capacity per unit energy of fading relay channels.