IEEE Communications Magazine • April 2015 20 0163-6804/15/$25.00 © 2015 IEEE Nan Yang is with the Aus- tralian National University. Lifeng Wang and M. Elkashlan are with Queen Mary University of London. Giovanni Geraci is with the Singapore University of Technology and Design. Jinhong Yuan is with the University of New South Wales. Marco Di Renzo is with Paris-Saclay University, Laboratory of Signals and Systems (UMR-8506), CNRS - CentraleSupelec - University Paris-Sud XI, 91192 Gif-sur-Yvette (Paris), France. INTRODUCTION Mobile wireless communication has experi- enced an unprecedented growth in data traffic in recent years, spurred by the popularity of various intelligent devices, the demand for exu- berant multimedia content, and the rapid increase in the number of base stations (BSs). In particular, global mobile data traffic in 2013 was nearly 18 times the size of the entire glob- al Internet in 2000, and monthly global mobile data traffic by 2018 will surpass 15 exabytes [1]. While the mature third generation network and the currently deploying fourth generation (4G) network may accommodate the data traf- fic surge for the next few years, they will not be able to support a very large number of devices with a huge network traffic demand in 2020 and beyond [2]. Against this backdrop, a number of disruptive trends and technologies shaping the fifth generation (5G) network are emerging worldwide through research and development. For example, academia is researching robust and efficient wireless trans- mission technologies for the 5G era, such as the heterogeneous network (HetNet), massive multiple-input multiple-output (MIMO), and millimeter wave (mmWave). At the same time, the industry is undertaking 5G standardization. Given the ubiquitousness and necessity of 5G connections in the near future, an enormous amount of sensitive and confidential informa- tion, e.g. financial data, electronic media, med- ical records, and customer files, will be transmitted via wireless channels. Thus, provid- ing an unrivalled security service is one of the top priorities in the design and implementation of the 5G network. Despite the current efforts from academia and industry, the security paradigms protecting the confidentiality of wireless communication in the 5G network remain elusive. Indeed, how to secure wireless data transmission is one of the core problems that any 5G network designer can face. Differing from the traditional approach which protects data security through cryptographic techniques, physical layer security is identified as a promising strategy that pro- vides secure wireless transmissions by smartly exploiting the imperfections of the communica- tions medium. Using this strategy, 5G network designers can effectively degrade the quality of signal reception at unauthorized receivers and devices, and therefore prevent them from acquiring confidential information from the received signal. With careful planning and exe- cution, physical layer security will protect the communication phase of the network while cryptography will protect the processed data after the communication phase. As such, they will form a well-integrated security solution that efficiently safeguards sensitive and confidential data for the 5G era. Notably, physical layer security offers two major advantages compared to cryptography, making it particularly suitable for the 5G net- work. First, physical layer security techniques do not depend on computational complexity, which implies that the achieved level of security will not be compromised even if the unautho- ABSTRACT The fifth generation (5G) network will serve as a key enabler in meeting the continuously increasing demands for future wireless applica- tions, including an ultra-high data rate, an ultra- wide radio coverage, an ultra-large number of devices, and an ultra-low latency. This article examines security, a pivotal issue in the 5G net- work where wireless transmissions are inherently vulnerable to security breaches. Specifically, we focus on physical layer security, which safeguards data confidentiality by exploiting the intrinsic randomness of the communications medium and reaping the benefits offered by the disruptive technologies to 5G. Among various technologies, the three most promising ones are discussed: heterogenous networks, massive multiple-input multiple-output, and millimeter wave. On the basis of the key principles of each technology, we identify the rich opportunities and the out- standing challenges that security designers must tackle. Such an identification is expected to deci- sively advance the understanding of future physi- cal layer security. SECURITY AND PRIVACY IN EMERGING NETWORKS Nan Yang, Lifeng Wang, Giovanni Geraci, Maged Elkashlan, Jinhong Yuan, and Marco Di Renzo Safeguarding 5G Wireless Communication Networks Using Physical Layer Security