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FLEX: Joint UL/DL and QoS-Aware Scheduling for Dynamic TDD in Industrial 5G and Beyond

Leonard Kleinberger, Michael Gundall, Hans D. Schotten

Abstract

Industrial 5G deployments using Time Division Duplex (TDD) networks face a critical challenge: existing schedulers rely on static configuration of Uplink (UL) to Downlink (DL) resource ratios, failing to adapt to dynamic asymmetric traffic demands. This limitation is particularly problematic in Industry 4.0 scenarios where traffic patterns exhibit significant asymmetry between directions and heterogeneous Quality of Service (QoS) requirements. We present FLEX, a novel QoS-aware scheduler that dynamically adjusts the UL/DL ratio in flexible TDD slots while respecting diverse QoS requirements. FLEX introduces DL buffer state estimation to prevent starvation of high-priority DL traffic, exploiting the deterministic nature of industrial traffic patterns for accurate predictions. Through extensive simulations of industrial scenarios using 5G LENA and ns-3, we demonstrate that FLEX achieves similar throughput compared to established scheduling while correctly enforcing QoS priorities in both traffic directions. For deterministic traffic patterns, FLEX maintains minimal latency overhead (less than 1 slot duration), making it particularly suitable for industrial automation applications.

FLEX: Joint UL/DL and QoS-Aware Scheduling for Dynamic TDD in Industrial 5G and Beyond

Abstract

Industrial 5G deployments using Time Division Duplex (TDD) networks face a critical challenge: existing schedulers rely on static configuration of Uplink (UL) to Downlink (DL) resource ratios, failing to adapt to dynamic asymmetric traffic demands. This limitation is particularly problematic in Industry 4.0 scenarios where traffic patterns exhibit significant asymmetry between directions and heterogeneous Quality of Service (QoS) requirements. We present FLEX, a novel QoS-aware scheduler that dynamically adjusts the UL/DL ratio in flexible TDD slots while respecting diverse QoS requirements. FLEX introduces DL buffer state estimation to prevent starvation of high-priority DL traffic, exploiting the deterministic nature of industrial traffic patterns for accurate predictions. Through extensive simulations of industrial scenarios using 5G LENA and ns-3, we demonstrate that FLEX achieves similar throughput compared to established scheduling while correctly enforcing QoS priorities in both traffic directions. For deterministic traffic patterns, FLEX maintains minimal latency overhead (less than 1 slot duration), making it particularly suitable for industrial automation applications.
Paper Structure (18 sections, 3 equations, 5 figures, 1 table)

This paper contains 18 sections, 3 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Related Work
  3. System Model and Key Challenges
  4. 5G TDD Architecture
  5. UL Scheduling Procedure
  6. The DL Starvation Problem
  7. QoS Requirements
  8. FLEX Scheduler Design
  9. Bidirectional Traffic Measurement
  10. Buffer State Estimation
  11. Joint UL/DL Scheduling Procedure
  12. DL Scheduling Re-evaluation
  13. Evaluation
  14. Simulation Setup
  15. Scenario 1: Motion Control
  16. ...and 3 more sections

Figures (5)

  • Figure 1: The timeline for a data transmission in 5G systems. Control information is sent via DCI before the actual data transmission. The UL DCI Deadline is before the DL DCI Deadline.
  • Figure 2: Activity diagram for the scheduling procedure. Resources are assigned one-by-one to the UE with the highest priority.
  • Figure 3: PLR for different numbers of UEs in scenario 1. Lower is better. FLEX offers significantly improved performance for more than 10 UEs.
  • Figure 4: PLR for different numbers of UEs in scenario 2. Lower is better. FLEX offers significantly improved performance for a high number of UEs.
  • Figure 5: PLR per traffic direction in scenario 3. Lower is better. DL traffic has a higher priority and DL PLR should remain lower than UL traffic PLR.