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To Sense or Not To Sense: A Delay Perspective (full version)

Xinran Zhao, Lin Dai

TL;DR

This work addresses low-latency access in dense M2M settings by presenting a unified HOL-packet Markov renewal framework that encompasses sensing-free Aloha and sensing-based CSMA with backoff and connection modes. It provides explicit expressions for the minimum mean queueing delay $\overline{T}_{\min}$ and the optimal initial transmission probability $q_0^{\ast}$, along with a delay-optimal sensing bound $\tilde{\sigma}_C^{\ast}$ that depends on the aggregate input rate $\tilde{\lambda}$, the number of nodes $n$, and the backoff scheme. The paper demonstrates how sensing can improve delay performance, deriving theoretical bounds and validating them through 5G RA-SDT case studies, where sensing notably reduces delay, especially for grant-free 2-step schemes and with Binary Exponential Backoff. These insights offer practical guidance for designing low-latency random-access protocols in massive MTD deployments and beyond.

Abstract

With the ever-growing demand for low-latency services in machine-to-machine (M2M) communications, the delay performance of random access networks has become a primary concern, which critically depends on the sensing capability of nodes. To understand the effect of sensing on the optimal delay performance, the challenge lies in unifying the delay analysis of sensing-free Aloha and sensing-based Carrier Sense Multiple Access (CSMA) with various design features such as backoff and connection-free or connection-based. In this paper, based on a unified analytical framework, the mean queueing delay of data packets with Aloha and CSMA is characterized and optimized, with which the upper-bound of sensing time for CSMA to outperform Aloha in terms of the minimum mean queueing delay is further obtained. The analysis is also applied to the Random Access-Based Small Data Transmission (RA-SDT) schemes in 5G networks to investigate when and how significant their delay performance can be improved by sensing, which sheds important insights into practical access protocol design.

To Sense or Not To Sense: A Delay Perspective (full version)

TL;DR

This work addresses low-latency access in dense M2M settings by presenting a unified HOL-packet Markov renewal framework that encompasses sensing-free Aloha and sensing-based CSMA with backoff and connection modes. It provides explicit expressions for the minimum mean queueing delay and the optimal initial transmission probability , along with a delay-optimal sensing bound that depends on the aggregate input rate , the number of nodes , and the backoff scheme. The paper demonstrates how sensing can improve delay performance, deriving theoretical bounds and validating them through 5G RA-SDT case studies, where sensing notably reduces delay, especially for grant-free 2-step schemes and with Binary Exponential Backoff. These insights offer practical guidance for designing low-latency random-access protocols in massive MTD deployments and beyond.

Abstract

With the ever-growing demand for low-latency services in machine-to-machine (M2M) communications, the delay performance of random access networks has become a primary concern, which critically depends on the sensing capability of nodes. To understand the effect of sensing on the optimal delay performance, the challenge lies in unifying the delay analysis of sensing-free Aloha and sensing-based Carrier Sense Multiple Access (CSMA) with various design features such as backoff and connection-free or connection-based. In this paper, based on a unified analytical framework, the mean queueing delay of data packets with Aloha and CSMA is characterized and optimized, with which the upper-bound of sensing time for CSMA to outperform Aloha in terms of the minimum mean queueing delay is further obtained. The analysis is also applied to the Random Access-Based Small Data Transmission (RA-SDT) schemes in 5G networks to investigate when and how significant their delay performance can be improved by sensing, which sheds important insights into practical access protocol design.
Paper Structure (29 sections, 78 equations, 10 figures, 1 table, 2 algorithms)

This paper contains 29 sections, 78 equations, 10 figures, 1 table, 2 algorithms.

Table of Contents

  1. Introduction
  2. Delay Analysis of Random Access Networks
  3. Access Delay
  4. Queueing Delay
  5. Our Contributions
  6. System Model
  7. Minimum Mean Queueing Delay of Data Packets
  8. Random Access: Sensing-Free versus Sensing-Based and Connection-Free versus Connection-Based
  9. Upper-Bound of Sensing Time for Beneficial Sensing
  10. HOL-Packet Modeling
  11. State Characterization of HOL Packets
  12. Aloha
  13. CSMA
  14. Steady-State Probabilities $\tilde{\alpha}$ and $p$
  15. Steady-State Probability $\tilde{\alpha}$
  16. ...and 14 more sections

Figures (10)

  • Figure 1: Graphic illustration of an $n$-node buffered random access network.
  • Figure 2: Graphic illustration of (a) connection-free Aloha and (b) connection-based Aloha.
  • Figure 3: Graphic illustration of (a) connection-free CSMA and (b) connection-based CSMA.
  • Figure 4: Embedded Markov chain $\mathbf{X^A}$ of the state transition process of an individual HOL packet in the Aloha network.
  • Figure 5: Embedded Markov chain $\mathbf{X^C}$ of the state transition process of an individual HOL packet in the CSMA network.
  • ...and 5 more figures