Different from conventional mobile network designs primarily optimizing the transmission efficiency of single service (e.g., voice/video streams), industry and academia have agreed with the manifold wireless features to be supported by the fifth-generation networks (5G). In September 2015, International Telecommunication Union-Radiocommunication Sector (ITU-R) has identified three categories for these upcoming wireless features: enhanced mobile broadband (eMBB), ultrareliable and low latency communications (URLLC), and massive machine-type communications (mMTC). In the meantime, ITU-R has also identified the radio transmission requirements of 5G (also known as International Mobile Telecommunications 2020, IMT-2020), including 20 Gbps peak data rate, 100 Mbps user experienced data rate, 10 Mbps/m² area traffic capacity, 10⁶ devices/km² connection density, 1 ms latency, and mobility up to 500 km/hr. To this end, 3GPP consequently launched the standardization activity of 5G New Radio (NR) in 2016 to frame Release 15 as the Phase-I 5G specifications. To satisfy these unprecedented radio transmission requirements, a number of technologies not involved in LTE-Advanced will be adopted by NR, including utilizing spectrum above 6 GHz (up to 100 GHz), beamforming in both control and user planes, gNBs with multiple remote transmission/reception points (TRPs), frame structure with agile resource arrangement, nonorthogonal multiple access (NOMA), and new waveforms. In Phase-II specifications (Release 16), NR sidelink transmissions, mobile backhaul, unlicensed access, ultradense network/access, and so forth are also projected to be supported. On the top of these new radio access technologies, network function virtualization (NFV), software-defined network (SDN), network slicing, open stack/architecture, and cloud/fog networks are also considerably studied for the next-generation core network. The purpose of this special issue is to bring together state-of-the-art innovations, research activities (both in academia and industry), and the corresponding standardization impacts of 5G so as to understand the inspirations, requirements, and the promising technical options to boost and enrich activities in the area of 5G.

Potential topics include but are not limited to the following:

• New waveforms, NOMA, multiuser superposition transmission (MUST), and beamforming based radio access
• Radio resource and interference management for eMBB, URLLC, and mMTC
• Ultradense network, multiple TRPs, cloud radio access network, and massive MIMO
• Sidelink, mobile backhaul, and unlicensed radio access
• SDN, NFV, network slicing, and open source/architecture for next-generation core
• Cloud/fog radio access networks
• Standardizations of 5G
• Simulation platform, prototypes, and field trial for 5G