  Caching popular contents at edge devices is an effective solution to
alleviate the burden of the backhaul networks. Earlier investigations commonly
neglected the storage cost in caching. More recently, retention-aware caching,
where both the downloading cost and storage cost are accounted for, is
attracting attention. Motivated by this, we address proactive and
retention-aware caching with user mobility, optimizing the sum of the two types
of costs. This is a combinatorial optimization problem. However, we derive a
stream of analytical results and they together lead to an algorithm that
guarantees global optimum with polynomial-time complexity. Numerical results
show significant improvements in comparison to popular caching and random
caching.
