5. Beamforming-Aided Cooperative Edge Caching in mmWave Dense Networks

Edge caching is a promising solution for reducing the content retrieval delay and relieving the backhaul traffic burden in ultradense networks. It achieves this objective by proactively caching popular contents on edge nodes, e.g., small base stations (SBSs). Yet, the amount of cache resources on each SBS is limited. In this chapter, we present a novel caching policy, named device-to-device (D2D) assisted cooperative edge caching (DCEC), for mmWave dense networks. In specific, a user can retrieve the requested content from neighboring users via D2D links, or from the neighboring SBSs via cellular links to efficiently exploit the cache diversity. In contrast to existing caching policies for networks in lower-frequency bands, which require complex interference management techniques, we take advantage of the directional mmWave antenna to ensure high transmission rate. We derive closed-form expressions of the backhaul offloading performance and content retrieval delay based on stochastic information of network topology. Analytical results indicate that, with the increase of network density, the content retrieval delay via D2D links increases significantly, while that via cellular links only increases slightly. Comprehensive simulations validate our theoretical analysis and demonstrate that the presented policy can effectively decrease backhaul traffic burden and reduce the content retrieval delay.