  As an extension of cloud computing, fog computing at the edge of networks
provides low latency, location awareness, and real-time interactions. At the
same time, millimeter wave (mmWave) communications are able to provide
directional multi-gigabit transmission rates with large available bandwidth.
Based on the user mobile trajectories in a region, several activity hotspots
that users pass by frequently can be obtained. By caching popular content at
the edge nodes near the hotspots, users can download the cached content
directly at a short distance, and the user experience can be significantly
improved. Considering multiple hotspots in a region, how to efficiently
schedule the transmission for the caching at edge nodes becomes a key problem.
In this paper, we focus on the problem of mobility aware transmission
scheduling for caching at edge nodes near hotspots, and utilize multi-hop
relaying and concurrent transmissions to achieve better performance. After
formulating the optimal scheduling problem as a stochastic nonlinear mixed
integer program, we propose a mobility aware caching scheduling scheme, called
MHRC (Multi-Hop Relaying based Caching), where multi-hop D2D paths are
established for edge nodes, and concurrent transmissions are exploited in the
scheduling of caching at edge nodes. Extensive performance evaluation
demonstrates MHRC achieves more than 1x higher expected cached data amount
compared with state-of-the-art schemes.
