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DMH-HARQ: Reliable and Open Latency-Constrained Wireless Transport Network

Bin Han, Muxia Sun, Yao Zhu, Vincenzo Sciancalepore, Mohammad Asif Habibi, Yulin Hu, Anke Schmeink, Yan-Fu Li, Hans D. Schotten

TL;DR

The DMH-HARQ framework targets reliable, latency-constrained wireless transport in URLLC-enabled 6G networks by rethinking HARQ across multi-hop DF relays. It models finite-blocklength reliability and frames an end-to-end optimization that couples retransmission and forwarding through a dynamic, symbol-level allocation of the remaining budget, solved via an integer dynamic programming approach. The authors develop LUT-enabled online implementations and demonstrate substantial end-to-end reliability gains over static HARQ and listening-based ARQ baselines, with practical considerations on complexity and timer overhead. The work aligns with Open-RAN openness and provides a pathway to robust wireless fronthaul/midhaul/backhaul in disaggregated 6G deployments, while outlining directions for incremental redundancy and multi-access integration.

Abstract

The extreme requirements for high reliability and low latency in the upcoming Sixth Generation (6G) wireless networks are challenging the design of multi-hop wireless transport networks. Inspired by the advent of the virtualization concept in the wireless networks design and openness paradigm as fostered by the Open-Radio Access Network (O-RAN) Alliance, we target a revolutionary resource allocation scheme to improve the overall transmission efficiency. In this paper, we investigate the problem of automatic repeat request (ARQ) in multi-hop decode-and-forward (DF) relaying in the finite blocklength (FBL) regime, and propose a dynamic scheme of multi-hop hybrid ARQ (HARQ), which maximizes the end-to-end (E2E) communication reliability in the wireless transport network. We also propose an integer dynamic programming (DP) algorithm to efficiently solve the optimal Dynamic Multi-Hop HARQ (DMH-HARQ) strategy. Constrained within a certain time frame to accomplish E2E transmission, our proposed approach is proven to outperform the conventional listening-based cooperative ARQ, as well as any static HARQ strategy, regarding the E2E reliability. It is applicable without dependence on special delay constraint, and is particularly competitive for long-distance transport network with many hops.

DMH-HARQ: Reliable and Open Latency-Constrained Wireless Transport Network

TL;DR

The DMH-HARQ framework targets reliable, latency-constrained wireless transport in URLLC-enabled 6G networks by rethinking HARQ across multi-hop DF relays. It models finite-blocklength reliability and frames an end-to-end optimization that couples retransmission and forwarding through a dynamic, symbol-level allocation of the remaining budget, solved via an integer dynamic programming approach. The authors develop LUT-enabled online implementations and demonstrate substantial end-to-end reliability gains over static HARQ and listening-based ARQ baselines, with practical considerations on complexity and timer overhead. The work aligns with Open-RAN openness and provides a pathway to robust wireless fronthaul/midhaul/backhaul in disaggregated 6G deployments, while outlining directions for incremental redundancy and multi-access integration.

Abstract

The extreme requirements for high reliability and low latency in the upcoming Sixth Generation (6G) wireless networks are challenging the design of multi-hop wireless transport networks. Inspired by the advent of the virtualization concept in the wireless networks design and openness paradigm as fostered by the Open-Radio Access Network (O-RAN) Alliance, we target a revolutionary resource allocation scheme to improve the overall transmission efficiency. In this paper, we investigate the problem of automatic repeat request (ARQ) in multi-hop decode-and-forward (DF) relaying in the finite blocklength (FBL) regime, and propose a dynamic scheme of multi-hop hybrid ARQ (HARQ), which maximizes the end-to-end (E2E) communication reliability in the wireless transport network. We also propose an integer dynamic programming (DP) algorithm to efficiently solve the optimal Dynamic Multi-Hop HARQ (DMH-HARQ) strategy. Constrained within a certain time frame to accomplish E2E transmission, our proposed approach is proven to outperform the conventional listening-based cooperative ARQ, as well as any static HARQ strategy, regarding the E2E reliability. It is applicable without dependence on special delay constraint, and is particularly competitive for long-distance transport network with many hops.
Paper Structure (27 sections, 3 theorems, 21 equations, 6 figures, 3 tables, 2 algorithms)

This paper contains 27 sections, 3 theorems, 21 equations, 6 figures, 3 tables, 2 algorithms.

Table of Contents

  1. Introduction
  2. Related Work
  3. Problem Setup
  4. Multi-Hop DF and DMH-HARQ
  5. Binary Schedule Tree
  6. Optimization Problem
  7. Analyses: Type I HARQ without Combining
  8. Error Model, Constraints, and Approximations
  9. Multi-Hop Link Reliability with Perfect Global CSI
  10. Multi-Hop Link Reliability with Imperfect CSI
  11. Algorithm Design
  12. Optimal DMH-HARQ: Integer Dynamic Programming
  13. Hop-by-Hop CSI Update and Reschedule
  14. Computational Complexity Analysis
  15. Numerical Evaluation
  16. ...and 12 more sections

Key Result

Lemma 1

With Type I HARQ without combining, $n_{\mathrm{opt}}(s)$ is independent from $k_s$ or $\tau_s$, but determined by $t_s$ and $i_s$, i.e. $n_{\mathrm{opt}}(s)=n^{\mathrm{opt}}_{i_s}(t_s)$.

Figures (6)

  • Figure 1: A conceptual depiction of the O-RAN architecture is presented. This article concentrates on the areas outlined by the dashed blue box, where the proposed transmission scheme enhances E2E communication reliability.
  • Figure 2: Part of a DMH-HARQ schedule for 4-hop DF chain, beginning with the initial state $s_0=(T_{\mathrm{max}},4,0,0)$. At each (re)transmission attempt, an optimal blocklength is calculated for consumption, and a fixed time for decoding and feedback is required. Upon the decoding result, the remaining (reserved) blocklength is dynamically assigned regarding the decoding result: either for next hops upon success (ACK), or for retransmission on the same hop upon failure (NACK). The states $s_0$, $s_1$, and $s_2$ are illustrated with time frame details.
  • Figure 3: Illustration of baseline solutions for 4-hop DF chain.
  • Figure 4: Sensitivity tests regarding (\ref{['subfig:frame_length_test']}) the time frame length, (\ref{['subfig:num_hops_test']}) the number of hops, (\ref{['subfig:dec_delay_test']}) the decoding/feedback delay, and (\ref{['subfig:path_loss_test']}) the pathloss, respectively.
  • Figure 5: Sensitivity test regarding the CSI quantization levels.
  • ...and 1 more figures

Theorems & Definitions (5)

  • Lemma 1
  • Lemma 2
  • Theorem 1
  • proof
  • proof