Non-orthogonal HARQ for URLLC Design and Analysis

TL;DR

This paper introduces a non-orthogonal HARQ scheme for 5G URLLC that improves reliability and reduces latency by sharing time slots non-orthogonally, outperforming conventional HARQ in delay performance.

Contribution

It proposes a novel non-orthogonal HARQ mechanism and an optimization framework, enhancing reliability and latency in URLLC scenarios compared to traditional methods.

Findings

High performance gain in packet delay over conventional HARQ

Effective in both AWGN and Rayleigh fading channels

Optimization improves retransmission efficiency

Abstract

The fifth-generation (5G) of mobile standards is expected to provide ultra-reliability and low-latency communications (URLLC) for various applications and services, such as online gaming, wireless industrial control, augmented reality, and self driving cars. Meeting the contradictory requirements of URLLC, i.e., ultra-reliability and low-latency, is considered to be very challenging, especially in bandwidth-limited scenarios. Most communication strategies rely on hybrid automatic repeat request (HARQ) to improve reliability at the expense of increased packet latency due to the retransmission of failing packets. To guarantee high-reliability and very low latency simultaneously, we enhance HARQ retransmission mechanism to achieve reliability with guaranteed packet level latency and in-time delivery. The proposed non-orthogonal HARQ (N-HARQ) utilizes non-orthogonal sharing of time slots for conducting retransmission. The reliability and delay analysis of the proposed N-HARQ in the finite block length (FBL) regime shows very high performance gain in packet delivery delay over conventional HARQ in both additive white Gaussian noise (AWGN) and Rayleigh fading channels. We also propose an optimization framework to further enhance the performance of N-HARQ for single and multiple retransmission cases.