In this chapter, we discuss the application of edge caching to enhance the physical layer security of cellular networks with limited backhaul capacity. By proactively sharing the same content across a subset of base stations (BSs) through both caching and backhaul loading, secure cooperative multiple-input multiple-output (MIMO) transmission of several BSs can be dynamically enabled in accordance with the cache status, the channel conditions, and the backhaul capacity. We formulate a two-stage nonconvex optimization problem for minimizing the total transmit power while providing quality of service (QoS) and guaranteeing communication secrecy during content delivery, where the caching and the cooperative MIMO transmission policy are optimized in an offline caching stage and an online delivery stage, respectively. Caching is shown to be beneficial as it reduces the data sharing overhead imposed on the capacity-constrained backhaul links, introduces additional secure degrees of freedom, and enables a power-efficient communication system design.

This chapter studies the potential of physical layer security in future ultra-dense networks. The unique features of ultra-dense networks are summarized, which can be exploited to enhance the secure transmission at the physical layer. We illustrate that physical layer security can be implemented in many use cases such as vehicle-to-everything, edge computing and caching services, to safeguard the confidential messages. The opportunities and challenges in these research areas are presented.