Caching and Multicasting in Large-Scale Cache-Enabled Heterogeneous Wireless Networks

Abstract

Heterogeneous wireless networks (HetNets) provide a powerful approach to meet the dramatic mobile traffic growth, but also impose a significant challenge on backhaul. Caching and multicasting at macro and pico base stations (BSs) are two promising methods to support massive content delivery and reduce backhaul load in HetNets. In this paper, we jointly consider caching and multicasting in a large-scale cache-enabled HetNet with backhaul constraints. We propose a hybrid caching design to provide high spatial file diversity and a corresponding multicasting design for efficient content dissemination. By carefully handling different types of interferers, we derive tractable expressions for the successful transmission probability in the general signal-to-noise ratio (SNR) and user density region as well as the high SNR and user density region, utilizing tools from stochastic geometry. Then, we consider the successful transmission probability maximization by optimizing the design parameters, which is a very challenging mixed discrete-continuous optimization problem. By exploring the structural properties, we obtain a near optimal solution with superior performance and manageable (polynomial) complexity, based on a two-step optimization framework. The analysis and optimization results provide valuable design insights for practical cache-enabled HetNets.