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Adaptive Finite Blocklength for Low Access Delay in 6G Wireless Networks

Yixin Zhang, Wenchi Cheng, Wei Zhang

TL;DR

The paper tackles the challenge of meeting massive ultra-low latency requirements for mURLLC in 6G by integrating grant-free random access with finite blocklength transmission through an adaptive blocklength framework. It derives closed-form expressions for successful access and packet transmission probabilities, and models the GF-based status update process with a discrete-time Markov chain, formulating an alternating-optimization algorithm to minimize average access delay by adapting blocklengths per packet as load varies. The approach uses $n=TW$ and the FB rate $R(n)$, balancing transmission and queuing delays to achieve lower latency than fixed-blocklength LTE/5G NR schemes. Numerical results confirm substantial delay reductions and illustrate the framework's responsiveness to real-time load, underscoring its practical value for 6G mURLLC deployments.

Abstract

As the number of real-time applications with ultra-low delay requirements quickly grows, massive ultra-reliable and low-latency communication (mURLLC) has been proposed to provide a wide range of delay-sensitive services for the sixth generation (6G) wireless networks. However, it is difficult to meet the stringent delay demand of massive connectivity with existing grant-based (GB) random access and fixed frame structure in long-term evolution (LTE) and the fifth generation (5G) new radio (NR) systems. To solve this problem, in this paper we propose the new grant-free (GF) based adaptive blocklength scheme for short packet transmission to reduce the access delay. We develop the adaptive blocklength framework where the blocklength can be adaptively changed according to the real-time load, to revise the traditional non-flexible frame structure which impacts the delay performance. Taking the features of mURLLC into consideration, we analyze the GF random access procedure, packet arrival behavior, packet collision, and packet transmission error in the finite blocklength (FB) regime. On this basis, we derive the closed-form expression of successful access and transmission probability and give the GF-based status update model. Then, we propose the access delay minimization problem that jointly considers queuing delay and transmission delay to reduce the overall access delay. With the alternating optimization algorithm, we obtain the optimal blocklength of each packet, thus forming the corresponding adaptive blocklength scheme for mURLLC. Simulation results verify the correctness of theoretical results and show that our proposed adaptive blocklength scheme can significantly reduce the access delay compared with that of LTE and 5G NR systems.

Adaptive Finite Blocklength for Low Access Delay in 6G Wireless Networks

TL;DR

The paper tackles the challenge of meeting massive ultra-low latency requirements for mURLLC in 6G by integrating grant-free random access with finite blocklength transmission through an adaptive blocklength framework. It derives closed-form expressions for successful access and packet transmission probabilities, and models the GF-based status update process with a discrete-time Markov chain, formulating an alternating-optimization algorithm to minimize average access delay by adapting blocklengths per packet as load varies. The approach uses and the FB rate , balancing transmission and queuing delays to achieve lower latency than fixed-blocklength LTE/5G NR schemes. Numerical results confirm substantial delay reductions and illustrate the framework's responsiveness to real-time load, underscoring its practical value for 6G mURLLC deployments.

Abstract

As the number of real-time applications with ultra-low delay requirements quickly grows, massive ultra-reliable and low-latency communication (mURLLC) has been proposed to provide a wide range of delay-sensitive services for the sixth generation (6G) wireless networks. However, it is difficult to meet the stringent delay demand of massive connectivity with existing grant-based (GB) random access and fixed frame structure in long-term evolution (LTE) and the fifth generation (5G) new radio (NR) systems. To solve this problem, in this paper we propose the new grant-free (GF) based adaptive blocklength scheme for short packet transmission to reduce the access delay. We develop the adaptive blocklength framework where the blocklength can be adaptively changed according to the real-time load, to revise the traditional non-flexible frame structure which impacts the delay performance. Taking the features of mURLLC into consideration, we analyze the GF random access procedure, packet arrival behavior, packet collision, and packet transmission error in the finite blocklength (FB) regime. On this basis, we derive the closed-form expression of successful access and transmission probability and give the GF-based status update model. Then, we propose the access delay minimization problem that jointly considers queuing delay and transmission delay to reduce the overall access delay. With the alternating optimization algorithm, we obtain the optimal blocklength of each packet, thus forming the corresponding adaptive blocklength scheme for mURLLC. Simulation results verify the correctness of theoretical results and show that our proposed adaptive blocklength scheme can significantly reduce the access delay compared with that of LTE and 5G NR systems.
Paper Structure (19 sections, 20 equations, 5 figures, 1 algorithm)

This paper contains 19 sections, 20 equations, 5 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model
  3. Grant-free Random Access Procedure
  4. Transmission Model
  5. Pakcet Arrival Model
  6. Adaptive Blocklength Framework
  7. Blocklength Structure And The Achievable Rate
  8. Adaptive Blocklength Design
  9. Packet Error Probability
  10. Packet Collision Avoidance Probability
  11. Successful Access and Transmission Probability
  12. Status Update Model
  13. Access Delay Minimization Problem
  14. Access Delay Reformulation
  15. Access Delay Minimization Problem Formulation
  16. ...and 4 more sections

Figures (5)

  • Figure 1: The grant-free random access system model.
  • Figure 2: The Markov chain based status update model.
  • Figure 3: Changes in the successful access and transmission probability and the blocklength of the adaptive blocklength scheme.
  • Figure 4: The access delay of the proposed adaptive blocklength scheme versus the number of users compared with that of LTE and 5G NR.
  • Figure 5: The access delay of the proposed adaptive blocklength scheme versus the bit number of one short packet and arrival rate compared with that of LTE and 5G NR.