Joint Caching and Multicast for Wireless Fronthaul in Fog Radio Access Networks

Content caching at enhanced Remote Radio Heads (eRRHs) has demonstrated significant benefits in alleviating tremendous burden on fronthaul in Fog Radio Access Networks (F-RANs). However, many existing works focus on caching the most popular contents at each eRRH individually and overlook the important fact, that connecting ultra dense eRRHs via wired fronthaul links is inconvenient and cost-prohibitive. Hence, it is vital that considering caching at eRRHs with wireless fronthaul. In this paper, we investigate the jointly application of content caching at eRRHs and content delivery via multicast for wireless fronthaul, which efficient exploits the inherent multicast capability of wireless channel, and the feature that a cluster of eRRHs may request the same content. Our objective is to minimize the transmission time for cloud processor (CP) while satisfying the average content requests with Quality of Experience (QoE) guarantee. The formulated problem boils down to a complicated mixed-integer non-linear programming (MINLP) problem, which is generally a NP-hard problem. Hence, we relax and approximate the MINLP problem to a tractable one, and propose a novel heuristic algorithm with a low-complexity. Numerical results demonstrate our proposed algorithms outperforms the existing individual content popularity based caching and wireless fronthaul scheme.