Safeguarding the Ultra-dense Networks with the aid of Physical Layer Security: A review and a case study

In the wake of the extensive application of the fourth generation system, investigations of new technologies have been moving ahead vigorously to embrace the next generation communications in 2020. Thereinto, the technique of ultra-dense networks (UDNs) serves as a key enabler in meeting the roaring mobile traffic demands. With the prevalence of mobile Internet services especially those involve the mobile payment, security has gained an unprecedented amount of attention and become a highlighted feature for the fifth generation. Resource allocation, one of the most significant tools on getting over the obstacle of ubiquitous interference as well as elevating the spectrum/energy efficiency, has attracted substantial efforts, whereas not much of them consider the information security. In a word, security-oriented resource allocation is a non-ignorable field in UDNs resource management, which still needs further study. This paper takes the safety performance as the pivotal issue and refers to the core idea of physical layer security, trying to pave a way for the security design under the framework of the densified networks. In particular, a review of the classical techniques in physical layer security is given from the perspective of resource allocation, which may enlighten the security-based resource management in UDNs. Besides, the challenges as well as potential problems are identified on the basis of the characteristics of UDNs, which can be favorable for targeting the future efforts. In a case study, it is shown that effective blockage of the eavesdropper in UDNs is achievable with the aid of physical layer security, and that the spectrum efficiency is also improved through the careful resource allocation.