Reliability Modeling for Beyond-5G Mission Critical Networks Using Effective Capacity

TL;DR

The paper tackles reliable operation for URLLC/HRLLC in Beyond-5G/6G by formulating a reliability model that couples 5G link-layer dynamics (RLC/MAC) with PHY using the effective capacity ($EC$) framework. It extends $EC$ to a dual-buffer RLC AM system with separate TX and RETX buffers, deriving delay-aware reliability expressions across multiple transmission attempts and decomposing latency into deterministic and stochastic components. An optimization framework balances $EC$ and reliability under a target $R_{th}$, identifying a feasible operating region for the delay exponent $\theta$ that preserves QoS while keeping $EC$ near its peak. The results provide concrete guidance on how many retransmissions to permit, how QoS constraints shape system performance, and how to design URLLC networks with practical tradeoffs across diverse use cases.

Abstract

Accurate reliability modeling for ultra-reliable low latency communication (URLLC) and hyper-reliable low latency communication (HRLLC) networks is challenging due to the complex interactions between network layers required to meet stringent requirements. In this paper, we propose such a model. We consider the acknowledged mode of the radio link control (RLC) layer, utilizing separate buffers for transmissions and retransmissions, along with the behavior of physical channels. Our approach leverages the effective capacity (EC) framework, which quantifies the maximum constant arrival rate a time-varying wireless channel can support while meeting statistical quality of service (QoS) constraints. We derive a reliability model that incorporates delay violations, various latency components, and multiple transmission attempts. Our method identifies optimal operating conditions that satisfy URLLC/HRLLC constraints while maintaining near-optimal EC, ensuring the system can handle peak traffic with a guaranteed QoS. Our model reveals critical trade-offs between EC and reliability across various use cases, providing guidance for URLLC/HRLLC network design for service providers and system designers.

Figures (4)

• Figure 1: System model and the exponential approximation of tail regions.
• Figure 2: Delay components between gNB and UE
• Figure 3: Effective capacity and Reliability trade-offs
• Figure 4: Optimal range $[\theta_{\text{min}}, \theta_{\text{max}}]$ with $R \geq R_{\text{th}}$