Future fifth generation (5G) mobile networks denote the next generation mobile networks beyond the current 4G mobile networks. The 5G networks are provisioned by the Next Generation Mobile Networks Alliance to provide much higher capacity and support various types of emerging applications with stringent quality of service (QoS) requirements. For example, on‐demand video streaming for entertainment needs to be delivered by 5G mobile networks. Another example is the machine‐oriented application. Billions of devices form the so‐called Internet of Things (IoT), which are used in e‐health system, smart city, and so on to make our daily life more efficient and comfortable. These applications have extremely diverse requirements in terms of capacity, latency, data rate, and energy cost.

How to design the 5G network to support these applications is an interesting and challenging issue. Looking back to previous generations (1G‐4G), each of them was dominated by single type of technologies (e.g., 3G technologies include CDMA2000, WIMAX, and UMTS‐HSPA; 4G mainly relies on LTE/LTE‐A and 802.16m). For 5G, single types of technologies cannot provide diverse QoS requirements across different applications. The 5G network can only be achieved by integrating various types of technologies, including new and existing technologies. For example, we could use millimeter‐wave communication which has very large bandwidth (multiple gigahertzes) to support much higher data rates and overwhelming capacity. The exploration of this new frequency band can be achieved by cognitive radio technology, which allows wireless devices to dynamically switch the radios to underutilized bands. At the same time, we should also leverage existing security and privacy technologies and provide heightened security and privacy in 5G.

The objective of this special issue is to solicit the state‐of‐art research contributions that present key and emerging results on 5G enabling technologies to optimize spectrum efficiency and provide heightened security and privacy.

Potential topics include but are not limited to the following:

• Network architectures design for 5G
• System environment study for device‐to‐device (D2D), machine‐to‐machine (M2M), and Internet of things (IoT)
• Wireless communication technologies for 5G (millimeter‐wave communications, massive MIMO, and full‐duplex)
• Cognitive radio technology
• Spectrum sharing and aggregation
• Security and privacy in 5G networks