Power Allocation for Type-I ARQ Two-Hop Cooperative Networks for Ultra-Reliable Communication

TL;DR

This paper derives outage probability expressions and proposes an optimal power allocation scheme for two-hop cooperative ARQ systems, significantly improving power efficiency for ultra-reliable communications.

Contribution

It introduces a closed-form optimal power allocation method for AF-ARQ in two-hop systems, enhancing reliability and power efficiency over existing schemes.

Findings

The optimal power allocation reduces power consumption compared to equal power strategies.

The scheme achieves target outage probabilities with minimized average power.

Significant power gains are demonstrated over point-to-point ARQ and equal power allocation.

Abstract

We analyze the performance of amplify-and-forward (AF) automatic repeat request (ARQ) for a two-hop cooperative system with reliability constrains. For this setup, we first derive the closed-form outage probability expression. Next, we present a power allocation scheme that allows us to achieve a target outage probability, while minimizing the outage-weighted average power expenditure for asymmetric power allocation between the source and relay. This is cast as an optimization problem, and the optimal power allocation (OPA) is obtained in closed form by invoking the Karush-Kuhn-Tucker (KKT) conditions. We evaluate numerically the OPA strategy between different AF-ARQ transmission rounds and we show that the proposed scheme provides large power gains with respect to the optimized point-to-point ARQ scheme, as well as with respect to the equal power allocation (EPA) strategy.