  In this paper, we investigate for the first time the benefits of wireless
caching for the physical layer security (PLS) of wireless networks. In
particular, a caching scheme enabling power-efficient PLS is proposed for
cellular video streaming with constrained backhaul capacity. By sharing video
data across a subset of base stations (BSs) through both caching and backhaul
loading, secure cooperative transmission of several BSs is dynamically enabled
in accordance with the cache status, the channel conditions, and the backhaul
capacity. Thereby, caching reduces the data sharing overhead over the
capacity-constrained backhaul links. More importantly, caching introduces
additional secure degrees of freedom and enables a power-efficient design. We
investigate the optimal caching and transmission policies for minimizing the
total transmit power while providing quality of service (QoS) and guaranteeing
secrecy during video delivery. A two-stage non-convex mixed-integer
optimization problem is formulated, which optimizes the caching policy in an
offline video caching stage and the cooperative transmission policy in an
online video delivery stage. As the problem is NP-hard, suboptimal
polynomial-time algorithms are proposed for low-complexity cache training and
delivery control, respectively. Sufficient optimality conditions, under which
the proposed schemes attain global optimal solutions, are also provided.
Simulation results show that the proposed schemes achieve low secrecy outage
probability and high power efficiency simultaneously.
