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ConPA: A Contention-free Mechanism with Power Adaptation for Beyond Listen-Before-Talk

Francesc Wilhelmi, Paolo Baracca, Gianluca Fontanesi, Lorenzo Galati-Giordano

TL;DR

This work tackles the challenge of achieving low latency and high reliability in unlicensed spectrum by moving beyond traditional LBT-based access. It introduces Contention-free with Power Adaptation (ConPA), a mechanism that bypasses contention and adapts transmit power based on measured interference to enhance airtime and throughput. An analytical framework based on Continuous-Time Markov Chains (CTMC) is developed to derive metrics such as throughput, airtime, and SINR, and ConPA is evaluated against DCF and 802.11ax OBSS/PD-based Spatial Reuse. Results show up to 76% throughput gains and substantial airtime improvements through spatial reuse, with some SINR tradeoffs at short range, underscoring ConPA’s potential for latency-critical deployments in the unlicensed bands.

Abstract

In view of the need to find novel means to utilize the unlicensed spectrum to meet the rising latency and reliability requirements of new applications, we propose a novel mechanism that allows devices to transmit anytime that a packet has to be delivered. The proposed mechanism, Contention-free with Power Adaptation (ConPA), aims to bypass the contention periods of current Listen-Before-Talk (LBT) approaches, which are the main source of unreliability in unlicensed technologies like Wi-Fi. To assess the feasibility of ConPA, we provide an analytical method based on Markov chains, which allows deriving relevant performance metrics, including throughput, airtime, and quality of transmissions. Using such a model, we study the performance of ConPA in various scenarios, and compare it to baseline channel access approaches like the Distributed Coordination Function (DCF) and the IEEE 802.11ax Overlapping Basic Service Set (OBSS) Packet Detect (PD)-based Spatial Reuse (SR). Our results prove the effectiveness of ConPA in reusing the space to offer substantial throughput gains with respect to the baselines (up to 76% improvement).

ConPA: A Contention-free Mechanism with Power Adaptation for Beyond Listen-Before-Talk

TL;DR

This work tackles the challenge of achieving low latency and high reliability in unlicensed spectrum by moving beyond traditional LBT-based access. It introduces Contention-free with Power Adaptation (ConPA), a mechanism that bypasses contention and adapts transmit power based on measured interference to enhance airtime and throughput. An analytical framework based on Continuous-Time Markov Chains (CTMC) is developed to derive metrics such as throughput, airtime, and SINR, and ConPA is evaluated against DCF and 802.11ax OBSS/PD-based Spatial Reuse. Results show up to 76% throughput gains and substantial airtime improvements through spatial reuse, with some SINR tradeoffs at short range, underscoring ConPA’s potential for latency-critical deployments in the unlicensed bands.

Abstract

In view of the need to find novel means to utilize the unlicensed spectrum to meet the rising latency and reliability requirements of new applications, we propose a novel mechanism that allows devices to transmit anytime that a packet has to be delivered. The proposed mechanism, Contention-free with Power Adaptation (ConPA), aims to bypass the contention periods of current Listen-Before-Talk (LBT) approaches, which are the main source of unreliability in unlicensed technologies like Wi-Fi. To assess the feasibility of ConPA, we provide an analytical method based on Markov chains, which allows deriving relevant performance metrics, including throughput, airtime, and quality of transmissions. Using such a model, we study the performance of ConPA in various scenarios, and compare it to baseline channel access approaches like the Distributed Coordination Function (DCF) and the IEEE 802.11ax Overlapping Basic Service Set (OBSS) Packet Detect (PD)-based Spatial Reuse (SR). Our results prove the effectiveness of ConPA in reusing the space to offer substantial throughput gains with respect to the baselines (up to 76% improvement).
Paper Structure (12 sections, 2 equations, 7 figures, 2 tables, 2 algorithms)

This paper contains 12 sections, 2 equations, 7 figures, 2 tables, 2 algorithms.

Table of Contents

  1. Introduction
  2. ConPA Design
  3. DCF and 802.11ax SR
  4. ConPA
  5. CTMC Characterization
  6. System Model
  7. Channel Model
  8. Packet Transmission Model
  9. Traffic Model
  10. Key Performance Indicators
  11. Performance Evaluation
  12. Conclusions

Figures (7)

  • Figure 1: Power mapping functions.
  • Figure 2: Channel access policies in an exemplary deployment.
  • Figure 3: CTMC representation of the 2-BSS deployment for the different considered channel access mechanisms. States and transitions for DCF (unaccessible in the showcased deployment), 802.11ax states, and ConPA states, are illustrated in foored!20 red, fooNavyBlue!30 blue, and fooForestGreen!30 green, respectively.
  • Figure 4: Average throughput achieved by $N=4$ APs (with $\alpha=1$) by ConPA for $D\in \{2,4,8\}$ m, $\text{C}\in \{-65, -70, -75, -80\}$, and $\alpha=1$.
  • Figure 5: Boxplot of various performance indicators achieved by each mechanism for $N \in \{2, 4\}$ BSSs, $D\in \{2,4,8\}$ m, and $\alpha=1$. The baseline performance of contention-free DCF (i.e., $N=1$ BSS) is shown by the red dashed lines.
  • ...and 2 more figures