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Fairness Scheduling for Coded Caching in Multi-AP Wireless Local Area Networks

Kagan Akcay, MohammadJavad Salehi, Giuseppe Caire

Abstract

Coded caching (CC) exploits cumulative cache memory at user devices and coding to transform unicast traffic into multicast transmissions. While information theoretic results show significant gains over uncoded caching for various network topologies, its practical benefits remain unclear. In this work, we investigate CC for on-demand video streaming over large wireless local area networks, where multiple users are served simultaneously by spatially distributed access points. Users asynchronously request video chunks from a content library. We propose a decentralized, asynchronous, and location-independent cache placement scheme combined with an "over IP" delivery mechanism operating at higher network layers, leaving the physical and MAC layers unchanged. For this scheme, we characterize the achievable goodput region, where goodput is defined as the number of video chunks per unit time delivered to users' playback buffers, and formulate the corresponding fairness problem as a convex maximization. We develop a dynamic scheduling algorithm that provably achieves the optimal fairness point under stationary conditions with reduced complexity, and introduce a heuristic to further lower complexity. Numerical results demonstrate significant gains over baseline schemes, including conventional prefix caching, orthogonal sub-channel allocation with spatial reuse, and a CSMA-inspired distributed coordination approach, showing that CC can be implemented as a scalable and compatible over IP solution for existing WLANs.

Fairness Scheduling for Coded Caching in Multi-AP Wireless Local Area Networks

Abstract

Coded caching (CC) exploits cumulative cache memory at user devices and coding to transform unicast traffic into multicast transmissions. While information theoretic results show significant gains over uncoded caching for various network topologies, its practical benefits remain unclear. In this work, we investigate CC for on-demand video streaming over large wireless local area networks, where multiple users are served simultaneously by spatially distributed access points. Users asynchronously request video chunks from a content library. We propose a decentralized, asynchronous, and location-independent cache placement scheme combined with an "over IP" delivery mechanism operating at higher network layers, leaving the physical and MAC layers unchanged. For this scheme, we characterize the achievable goodput region, where goodput is defined as the number of video chunks per unit time delivered to users' playback buffers, and formulate the corresponding fairness problem as a convex maximization. We develop a dynamic scheduling algorithm that provably achieves the optimal fairness point under stationary conditions with reduced complexity, and introduce a heuristic to further lower complexity. Numerical results demonstrate significant gains over baseline schemes, including conventional prefix caching, orthogonal sub-channel allocation with spatial reuse, and a CSMA-inspired distributed coordination approach, showing that CC can be implemented as a scalable and compatible over IP solution for existing WLANs.

Paper Structure

This paper contains 17 sections, 25 equations, 6 figures, 3 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Motivation and Prior Art
  3. Our Contributions
  4. System Model
  5. Coded Caching in Multi-AP Networks
  6. Placement Phase
  7. Delivery Phase
  8. Codeword Formation
  9. Instantaneous Rate Calculation
  10. Fairness Scheduling
  11. The Optimization Problem
  12. Complexity Reduction
  13. Dynamic Scheduling Solutions
  14. Reduced-Complexity Dynamic Solution
  15. The Virtual Queue Heuristic
  16. ...and 2 more sections

Figures (6)

  • Figure 1: Example network with $H=2$, $K=6$, and $L = 3$.
  • Figure 2: Example network with $H=7$, $K=70$. Each green user is within the transmission radius of exactly $1$ AP and outside the interference radii of other APs. Each blue user is within multiple AP transmission/interference radii.
  • Figure 3: Goodput geometric mean for different values of $L$ for PF, with $H=10$, $K_{avg}=200$, $\gamma=0.1$.
  • Figure 4: Goodput CDF for different values of $L$ for HF for the optimum solution, with $H=10$, $K_{avg}=200$, $\gamma=0.1$.
  • Figure 5: Goodput CDF comparison of PF and HF for the optimum solution, with $H=10$, $K_{avg}=200$, $\gamma=0.1$, $L=20$.
  • ...and 1 more figures

Theorems & Definitions (10)

  • Example 1
  • Remark 1
  • Example 2
  • Example 3
  • Remark 2
  • Example 4
  • Remark 3
  • Remark 4
  • Example 5
  • Example 6