Beef up mmWave Dense Cellular Networks with D2D-Assisted Cooperative Edge Caching

TL;DR

This paper proposes a D2D-assisted cooperative edge caching policy for mmWave dense networks, leveraging directional antennas and user cooperation to reduce content retrieval delay and backhaul load.

Contribution

It introduces a novel caching policy that combines user and SBS caches with D2D links, utilizing mmWave directional antennas to improve offloading and delay performance.

Findings

Higher backhaul offloading compared to MPC policy

Reduced content retrieval delay with increased network density

Analytical expressions validated by simulations

Abstract

Edge caching is emerging as the most promising solution to reduce the content retrieval delay and relieve the huge burden on the backhaul links in the ultra-dense networks by proactive caching popular contents in the small base station (SBS). However, constraint cache resource of individual SBSs significantly throttles the performance of edge caching. In this paper, we propose a device-to-device (D2D) assisted cooperative edge caching (DCEC) policy for millimeter (mmWave) dense networks, which cooperatively utilizes the cache resource of users and SBSs in proximity. In the proposed DCEC policy, a content can be cached in either users' devices or SBSs according to the content popularity, and a user can retrieve the requested content from neighboring users via D2D links or the neighboring SBSs via cellular links to efficiently exploit the cache diversity. Unlike existing cooperative caching policies in the lower frequency bands that require complex interference management techniques to suppress interference, we take advantage of directional antenna in mmWave systems to ensure high transmission rate whereas mitigating interference footprint. Taking the practical directional antenna model and the network density into consideration, we derive closed-form expressions of the backhaul offloading performance and content retrieval delay based on the stochastic information of network topology. In addition, analytical results indicate that, with the increase of the network density, the content retrieval delay via D2D links increases significantly while that via cellular links increases slightly. Comprehensive simulations validate our theoretical analysis and demonstrate that the proposed policy can achieve higher performance in offloading the backhaul traffic and reducing the content retrieval delay compared with the state-of-the-art most popular caching (MPC) policy.