Abstract

Caching content in small-cell networks can reduce the traffic congestion in backhaul. In this article, we develop a hybrid caching network comprising of unmanned aerial vehicles (UAVs) and ground small-cell base stations (SBSs), where UAVs are preferred because of their flexibility and elevated platform for line of sight. First, we derive the association probability for the ground user affiliated with a UAV and ground SBS. Then, we derive the successful content delivery probability by considering both the intercell and intracell interference. We also analyze the energy efficiency of the hybrid network and compare it with the separate UAV and ground networks. We further propose the caching scheme to improve the successful content delivery by managing the content popularity, where the part of the caching capacity in each UAV and ground SBS is reserved to store the most popular content (MPC), while the remaining stores less popular contents. Numerical results unveil that the proposed caching scheme has an improvement of 26.6% in content delivery performance over the MPC caching, which overlooks the impact of content diversity during caching.

Highlights

  • Wireless edge caching is one of the most promising solutions to backhaul congestion

  • In [8]– [11], unmanned aerial vehicles (UAVs) were distributed according to 3D Poisson point process (PPP) and the terrestrial network was modeled by PPP

  • The results reveal that the successful content delivery performance is dependent on the network parameters, such as the UAV and small-cell base stations (SBSs) density to control the interference and the UAV altitude, and on the content-related parameters, such as the size of the content in the database, caching capacity of UAVs and SBSs, skewness in content popularity, and the target data rate

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Summary

INTRODUCTION

In [8]– [11], UAVs were distributed according to 3D PPP and the terrestrial network was modeled by PPP Most of these studies ignore the caching aspect in UAVs. In [12], the authors provided an analytical framework using independent PPPs for UAV and ground BSs to evaluate the performance of UAV assisted cellular network in terms of signal-to-interference-plus-noise ratio (SINR) coverage probability. In [29], the authors studied the techniques to enhance the caching capacity in the mobile ad hoc networks These works did not consider the content placement scheme in UAV-enabled networks using the realistic AG channel conditions in urban environments. The existing studies mentioned above have neither considered the modeling of a hybrid caching network consisting of UAVs and ground SBSs randomly located according to the PPP [30], [31], nor analyzed its content delivery and energy efficiency performance. The content delivery performance of the proposed caching scheme is compared with the widely used popular content placement method in [22]– [25] as a baseline scheme which only cache MPC

Network Topology
Channel Model
Probabilistic Content Placement Scheme
INTERFERENCE CHARACTERIZATION
DERIVATION OF USER ASSOCIATION PROBABILITY
THE SUCCESSFUL CONTENT DELIVERY PROBABILITY
Successful Content Delivery Probability for the SBS in tier G
ENERGY EFFICIENCY OF HYBRID NETWORK
A HYBRID CACHING SCHEME
VIII. NUMERICAL RESULTS AND DISCUSSION
User Association Probability
Successful Content Delivery Performance
Energy Efficiency
Findings
CONCLUSION
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