Discrete Time Credit-Based Shaping for Time-Sensitive Applications in 5G/6G Networks

TL;DR

The paper tackles delivering deterministic end-to-end latency over wireless NR by adapting IEEE 802.1Qav CBS to a slot-based NR scheduler. It introduces two mechanisms, CBS-DT and CBS-PU, that govern per-UE credits with slot-accurate debits, ensuring bounded credit, preserved rate reservations, and worst-case delay guarantees. Theoretical analysis establishes stability, credit dominance, and deterministic pacing when used with round-robin scheduling, complemented by an event-driven implementation that scales with traffic events. 3GPP-conformant simulations show that both CBS variants tighten latency tails while maintaining class ordering and high resource utilization, with CBS-PU yielding especially efficient use by debiting only actually transmitted bytes. Overall, the work provides a practical, scalable path to exporting TSN-like determinism into 5G NR and future 6G networks.

Abstract

Future wireless networks must deliver deterministic end-to-end delays for workloads such as smart-factory control loops. On Ethernet these guarantees are delivered by the set of tools within IEEE 802.1 time sensitive networking~(TSN) standards. Credit-based shaper (CBS) is one such tool which enforces bounded latency. Directly porting CBS to 5G/6G New Radio (NR) is non-trivial because NR schedules traffic in discrete-time, modulation-dependent resource allocation, whereas CBS assumes a continuous, fixed-rate link. Existing TSN-over-5G translators map Ethernet priorities to 5G quality of service (QoS) identifiers but leave the radio scheduler unchanged, so deterministic delay is lost within the radio access network (RAN). To address this challenge, we propose a novel slot-native approach that adapts CBS to operate natively in discrete NR slots. We first propose a per-slot credit formulation for each user-equipment ({UE}) queue that debits credit by the granted transport block size~(TBS); we call this discrete-time CBS (CBS-DT). Recognizing that debiting the full {TBS} can unduly penalize transmissions that actually use only part of their grant, we then introduce and analyze {CBS} with Partial Usage ({CBS-PU}). {CBS-PU} scales the credit debit in proportion to the actual bytes dequeued from the downlink queue. The resulting CBS-PU algorithm is shown to maintain bounded credit, preserve long-term rate reservations, and guarantees worst-case delay performance no worse than {CBS-DT}. Simulation results show that slot-level credit gating--particularly CBS-PU--enables NR to export TSN class QoS while maximizing resource utilization.

Figures (6)

• Figure 1: CBS example with priorities $p_1$ (high) and $p_2$ (low)
• Figure 2: Per-UE CBS gating in 5G NR gNB downlink
• Figure 3: Overview of traffic arrivals and credit evolution.
• Figure 4: Empirical CDFs of downlink packet latency
• Figure 5: Per-UE downlink resource utilization efficiency ($\eta_u$) comparison at reduced load.

Theorems & Definitions (8)

• Theorem 1
• proof : Proof sketch
• Proposition 1: Worst-case per-slot cost
• proof : Justification
• Lemma 1: Safety of skipping
• Theorem 2: Amortized complexity
• proof : Proof sketch
• Lemma 2: Absolute waiting bounds