  In heterogeneous cellular networks with caching capability, due to mobility
of users and storage constraints of small-cell base stations (SBSs), users may
not be able to download all of their requested content from the SBSs within the
delay deadline of the content. In that case, the users are directed to the
macro-cell base station (MBS) in order to satisfy the service quality
requirement. Coded caching is exploited here to minimize the amount of data
downloaded from the MBS taking into account the mobility of the users as well
as the popularity of the contents. An optimal distributed caching policy is
presented when the delay deadline is below a certain threshold, and a
distributed greedy caching policy is proposed when the delay deadline is
relaxed.
