  A novel content caching strategy is proposed for a cache enabled
device-to-device (D2D) network where the user devices are allowed to
communicate using millimeter wave (mmWave) D2D links (> 6 GHz) as well as
conventional sub 6 GHz cellular links. The proposed content placement strategy
maximizes the successful content delivery probability of a line of sight D2D
link. Furthermore, a heuristic algorithm is proposed for efficient content
delivery. The overall scheme improves the successful traffic offloading gain of
the network compared to conventional cache-hit maximizing content placement and
delivery strategies. Significant energy efficiency improvements can also be
achieved in ultra-dense networks.
