  Recent years have witnessed an exponential growth of mobile data traffic,
which may lead to a serious traffic burn on the wireless networks and
considerable power consumption. Network densification and edge caching are
effective approaches to addressing these challenges. In this study, we
investigate joint long-term cache allocation and short-term content delivery in
cloud small cell networks (C-SCNs), where multiple smallcell BSs (SBSs) are
connected to the central processor via fronthaul and can store popular contents
so as to reduce the duplicated transmissions in networks. Accordingly, a
long-term power minimization problem is formulated by jointly optimizing
multicast beamforming, BS clustering, and cache allocation under quality of
service (QoS) and storage constraints. The resultant mixed timescale design
problem is an anticausal problem because the optimal cache allocation depends
on the future file requests. To handle it, a two-stage optimization scheme is
proposed by utilizing historical knowledge of users' requests and channel state
information. Specifically, the online content delivery design is tackled with a
penalty-based approach, and the periodic cache updating is optimized with a
distributed alternating method. Simulation results indicate that the proposed
scheme significantly outperforms conventional schemes and performs extremely
close to a genie-aided lower bound in the low caching region.
