  Recently, an evolution of the Cloud Radio Access Network (C-RAN) has been
proposed, named as Fog Radio Access Network (F-RAN). Compared to C-RAN, the
Radio Units (RUs) in F-CAN are equipped with local caches, which can store some
frequently requested files. In the downlink, users requesting the same file
form a multicast group, and are cooperatively served by a cluster of RUs. The
requested file is either available locally in the cache of this cluster or
fetched from the Central Processor (CP) via backhauls. Thus caching some
frequently requested files can greatly reduce the burden on backhaul links.
Whether a specific RU should be involved in a cluster to serve a multicast
group depends on its backhaul capacity, requested files, cached files and the
channel. Therefore it is subject to optimization. In this paper we investigate
the joint design of multicast beamforming, dynamic clustering and backhaul
traffic balancing. Beamforming and clustering are jointly optimized in order to
minimize the power consumed, while QoS of each user is to be met and the
traffic on each backhaul link is balanced according to its capacity.
