  In this paper, we investigate the problem of asynchronous coded caching in
fog radio access networks (F-RANs). To minimize the fronthaul load, the
encoding set collapsing rule and encoding set partition method are proposed to
establish the relationship between the coded-multicasting contents for
asynchronous and synchronous coded caching. Furthermore, a decentralized
asynchronous coded caching scheme is proposed, which provides asynchronous and
synchronous transmission methods for different delay requirements. The
closed-form expression of the fronthaul load is established for the special
case where the number of requests during each time slot is fixed, and the upper
and lower bounds of the fronthaul load are given for the general case where the
number of requests during each time slot is random. The simulation results show
that our proposed scheme can create considerable coded-multicasting
opportunities in asynchronous request scenarios.
