Guest Editors: Changle Li, Jun Fang, Kaizhi Huang, Zhi Quan, Chengwen Xing,Jianhua Zhang, Zhongshan Zhang, Liqiang Zhao, Yulong Zou

The ever increasing wireless data services, such as imaging, video, audio, multimedia, etc., have demands for the very high speed wireless communications and network, which are unfortunately a bottleneck when combining with the wireline core network. Users’ are now expecting high quality of experience with low-cost devices, ubiquitous connectivity, energy efficiency, high reliability, or even ultra-low latency if a vehicle terminal is applied.

As the thumb of rule, the generation of mobile communications network evolves every 10 years since 1980s.Both academy and industry are currently working towards the next-generation 5G wireless network, which is expected to be standardized and deployed in the next five years. Compared to the 4G wireless network, the 5th generation embraces the new coding theory, advanced signal processing technology, the expanded spectrum utilization, more sophisticated transceiver design, enhanced network infrastructure and optimized resource allocations. There have been plenty of the published literatures and demonstrations showing the improved spectral efficiency and system performance with the newly developed technologies.

This special issue targets at the most recent results from various aspects of 5G and formulating a mid-term report for the state of the art technologies. We have received a lot of contributions concerning massive MIMO,NOMA transmission, physical layer security, cognitive radio, 5G networking and so on. Based on the submissions and careful peer reviews, fourteen papers were selected for publication in this issue of China Communications.

The issue is divided into four categories: communications theories, signal processing for communications,networks, and emerging technologies & applications.In particular, the communications theories category has three articles. The article “Physical Layer Security with Its Applications in 5G Networks: A Review” presents a comprehensive review of the physical layer security techniques and discusses their applications in 5G networks.The article “Artificial Noise Aided Polar Codes for Physical Layer Security” proposes an artificial noise aided polar coding algorithm to improve the secrecy rate of polar codes for physical layer security. The article “Secure Transmission Scheme Based on Dual-Thresholds for Simultaneous Wireless Information and Power Transfer”studies a simultaneous wireless information and power transfer system with multiple external eavesdroppers and internal curious users.

The signal processing for communications category contains five articles. In particular, the article “Secure Spectral-Energy Efficiency Tradeoff in Random Cognitive Relay Networks” studies the spectrum efficiency and energy efficiency tradeoff for secure transmission in cognitive relay networks where all nodes are randomly distributed. The article “Flexible Uplink MU-MIMO Scheduling in Unlicensed Spectrum” investigates the uplink multi-user multiple-input multiple-output technique to achieve multiplexing gain in unlicensed spectrum. The article “Energy Efficient Constrained Shortest Path First-Based Joint Resource Allocation and Route Selection for Multi-hop CRNs” proposes an energy efficient constrained shortest path first based joint resource allocation and route selection algorithm to stress the importance of transmission hops and the tradeoff between data rate and power consumption. The article “Resource Allocation in D2D Aided High Speed Railway Wireless Communications Systems: A Matching Theory Approach” discusses the latest progress in high speed railway network to enable the implementation of the social network system.The article “Multi-User Detection for Spatial Modulation toward 5G Wireless Communications” designs a threshold-aided approximate message passing detector and a probability sorting aided approximate message passing detectors for multi-user spatial modulation.

The networks category contains three articles. The article “Clustering of Virtual Network Function Instances Oriented to Compatibility” brings a new way to dividing the instances of network functions virtualization with high compatibility into clusters used for 5G networks.The article “Contract-Based Content Delivery in 5G Converged Networks” proposes a contract-based content delivery scheme to maximize content provider profit in 5G converged networks. The article “Radio Access Net-work Slicing based on C/U Plane Separation” presents a novel RAN slicing scheme based on C/U plane separation, taking into account their correlation.

The last category focuses on emerging technologies &applications and contains three articles. The article “On Uplink Non-orthogonal Multiple Access for 5G: Opportunities and Challenges” analyzes the use cases and design targets of non-orthogonal multiple access technique for uplink data transmission. The article “Symbol Error Rate Performance Analysis of Non-Orthogonal Multiple Access for Visible Light Communications” presents the symbol error rate analysis of the visible light communications framework, where the non-orthogonal multiple access is employed to optimize the modulation mode.Last but not least, the article “Design and Implementation of a TDD-Based 128-Antenna Massive MIMO Prototype System” presents various aspects of a real implementation for a TDD-based massive MIMO prototype system with both the analytical signal model and link level simulation, including uplink video transmission,downlink beamforming, reciprocity calibration, as well as the comparisons with the state-of-the-art prototyping systems.

We would like to take this opportunity to thank the authors for their contributions, and also thank the reviewers for their diligent work. Their professional opinions are critical to ensure high quality of this special issue.