Optimization of ARQ Distribution for HARQ Strategies in Delay-Bounded Networks

TL;DR

This paper proposes a CC-HARQ based strategy for optimizing ARQ distribution in multi-hop networks with delay constraints, improving reliability especially in slow-fading channels by addressing intractability with approximation and low-complexity algorithms.

Contribution

It introduces a CC-HARQ based approach with an approximation method and necessary conditions for near-optimal ARQ distribution, along with a low-complexity solution algorithm.

Findings

CC-HARQ strategies outperform traditional ARQ in slow-fading channels.

The proposed approximation simplifies the optimization problem.

A low-complexity algorithm effectively finds near-optimal ARQ distribution.

Abstract

Inspired by several delay-bounded mission-critical applications, optimizing the end-to-end reliability of multi-hop networks is an important problem subject to end-to-end delay constraints on the packets. Towards that direction, Automatic Repeat Request (ARQ) based strategies have been recently proposed wherein the problem statement is to distribute a certain total number of ARQs (that capture end-to-end delay) across the nodes such that the end-to-end reliability is optimized. Although such strategies provide a fine control to trade end-to-end delay with end-to-end reliability, their performance degrades in slowly-varying channel conditions. Pointing at this drawback, in this work, we propose a Chase Combing Hybrid ARQ (CC-HARQ) based multi-hop network addressing the problem statement of how to distribute a certain total number of ARQs such that the end-to-end reliability is optimized. Towards solving the problem, first we identify that the objective function of the optimization problem is intractable due to the presence of Marcum-Q functions in it. As a result, we propose an approximation on the objective function and then prove a set of necessary and sufficient conditions on the near-optimal ARQ distribution. Subsequently, we propose a low-complexity algorithm to solve the problem for any network size. We show that CC-HARQ based strategies are particularly appealing in slow-fading channels wherein the existing ARQ strategies fail.