Towards URLLC with Proactive HARQ Adaptation

TL;DR

This paper introduces a Lyapunov-based adaptive HARQ protocol for beyond 5G URLLC, dynamically optimizing retransmissions to enhance latency and reliability without prior stochastic knowledge.

Contribution

It presents a novel proactive HARQ adaptation framework using Lyapunov optimization that improves latency and reliability in URLLC scenarios with time-varying channels.

Findings

Enhanced latency performance over reactive HARQ strategies

Maintains target reliability levels

Improves resource efficiency with dynamic retransmission control

Abstract

In this work, we propose a dynamic decision maker algorithm to improve the proactive HARQ protocol for beyond 5G networks. Based on Lyapunov stochastic optimization, our adaptation control framework dynamically selects the number of proactive retransmissions for intermittent URLLC traffic scenarios under time-varying channel conditions without requiring any prior knowledge associated with this stochastic process. It then better exploits the trade-off between Radio Access Network (RAN) latency, reliability and resource efficiency, which is still limited in its realization on current HARQ designs. We then evaluate the performance of several HARQ strategies and show that our proposal further improves latency over the reactive regime without affecting the resource efficiency such as fixed proactive retransmission while maintaining target reliability.