  This paper aims to characterize the synergy of distributed caching and
wireless fronthaul in a fog radio access network (Fog-RAN) where all edge nodes
(ENs) and user equipments (UEs) have a local cache and store contents
independently at random. The network operates in two phases, a file-splitting
based decentralized cache placement phase and a fronthaul-aided content
delivery phase. We adopt normalized delivery time (NDT) to characterize the
asymptotic latency performance with respect to cache size and fronthaul
capacity. Both an achievable upper bound and a theoretical lower bound of NDT
are obtained, and their multiplicative gap is within 12. In the proposed
delivery scheme, we utilize the fronthaul link, by exploiting coded
multicasting, to fetch both non-cached and cached contents to boost EN
cooperation in the access link. In particular, to fetch contents already cached
at ENs, an additional layer of coded multicasting is added on the coded
messages desired by UEs in the fronthaul link. Our analysis shows that the
proposed delivery scheme can balance the delivery latency between the fronthaul
link and access link, and is approximately optimum under decentralized caching.
