This chapter presents a content-centric framework for transmission optimization in cloud radio access networks (RANs) by leveraging wireless edge caching and physical-layer multicasting. We consider a cache-enabled cloud RAN, where each base station (BS) is equipped with a local cache and connected to a central processor (CP) via a backhaul link. The BSs acquire the requested contents either from their local caches or from the core network via the backhaul links. We first study the caching effects on multicast-enabled access downlink, where users requesting the same content are grouped together and served by the same BS or BS cluster using multicasting. We study the cache-aware joint design of the content-centric BS clustering and multicast beam-forming to minimize the system total power cost and backhaul cost subject to the quality-of-service (QoS) constraints for each multicast group.

Driven by the inherent spatiotemporal correlation in wireless data demand, cellular network design is becoming increasingly content-centric. An integral component of this new paradigm is the network's ability to cache popular content at its edge, which includes base stations, access points, and handheld devices. This additionally reduces latency, which is one of the key challenges facing the next generation of cellular networks. As discussed in the earlier chapters, the huge size of a typical library of popular files and the relatively smaller storage capacities of edge devices, especially small cell base stations (SCBSs) and handheld devices, make it necessary to carefully determine the set of files (cache) that should be placed on each device. Compared to a wireless network for which caching mechanisms are fairly well understood, a distinctive feature of content-centric wireless networks is the mobility of the end users, which needs to be included in the system design. Inspired by this, we investigate the impact of mobility on edge caching in this chapter.