A novel differential quasi-Yagi antenna is first presented and compared with a normal single-ended counterpart. The simulated and measured results show that the differential quasi-Yagi antenna outperforms the conventional single-ended one. The differential quasi-Yagi antenna is then used as an element for linear arrays. A study of the coupling mechanism between the two differential and the two single-ended quasi-Yagi antennas is conducted, which reveals that the TE₀ mode is the dominant mode, and the driver is the decisive part to account for the mutual coupling. Next, the effects of four decoupling structures are respectively evaluated between the two differential quasi-Yagi antennas. Finally, the arrays with simple but effective decoupling structures are fabricated and measured. The measured results demonstrate that the simple slit or air-hole decoupling structure can reduce the coupling level from -18 dB to -25 dB and meanwhile maintain the impedance matching and radiation patterns of the array over the broad bandwidth. The differential quasi-Yagi antenna should be a promising antenna candidate for many applications.

An improved parasitic parameter extraction method for InP high electron mobility transistor (HEMT) is presented. Parasitic parameter extraction is the first step of model parameter extraction and its accuracy has a great impact on the subsequent internal parameter extraction. It is necessary to accurately determine and effectively eliminate the parasitic effect, so as to avoid the error propagation to the internal circuit parameters. In this paper, in order to obtain higher accuracy of parasitic parameters, parasitic parameters are extracted based on traditional analytical method and optimization algorithm to obtain the best parasitic parameters. The validity of the proposed parasitic parameter extraction method is verified with excellent agreement between the measured and modeled S-parameters up to 40 GHz for InP HEMT. In 0.1–40 GHz InP HEMT, the average relative error of the optimization algorithm is about 9% higher than that of the analysis method, which verifies the validity of the parasitic parameter extraction method. The extraction of parasitic parameters not only provides a foundation for the high-precision extraction of small signal intrinsic parameters of HEMT devices, but also lays a foundation for the high-precision extraction of equivalent circuit model parameters of large signal and noise signals of HEMT devices.

Modern backup systems exploit data deduplication technology to save storage space whereas suffering from the fragmentation problem caused by deduplication. Fragmentation degrades the restore performance because of restoring the chunks that are scattered all over different containers. To improve the restore performance, the state-of-the-art History Aware Rewriting Algorithm (HAR) is proposed to collect fragmented chunks in the last backup and rewrite them in the next backup. However, due to rewriting fragmented chunks in the next backup, HAR fails to eliminate internal fragmentation caused by self-referenced chunks (that exist more than two times in a backup) in the current backup, thus degrading the restore performance. In this paper, we propose Selectively Rewriting Self-Referenced Chunks (SRSC), a scheme that designs a buffer to simulate a restore cache, identify internal fragmentation in the cache and selectively rewrite them. Our experimental results based on two real-world datasets show that SRSC improves the restore performance by 45% with an acceptable sacrifice of the deduplication ratio.

With the development and revolution of network in recent years, the scale and complexity of network have become big issues. Traditional hardware based network security solution has shown some significant disadvantages in cloud computing based Internet data centers (IDC), such as high cost and lack of flexibility. With the implementation of software defined networking (SDN), network security solution could be more flexible and efficient, such as SDN based firewall service and SDN based DDoS-attack mitigation service. Moreover, combined with cloud computing and SDN technology, network security services could be lighter-weighted, more flexible, and on-demanded. This paper analyzes some typical SDN based network security services, and provide a research on SDN based cloud security service (network security service pool) and its implementation in IDCs.

The demand for 5G services and applications is driving the change of network architecture. The mobile edge computing (MEC) technology combines the mobile network technology with cloud computing and virtualization, and is one of the key technologies for 5G networks. Compared to network function virtualization (NFV), another critical enabler of 5G networks, MEC reduces latency and enhances the offered capacity. In this paper, we discuss the combination of the two technologies and propose a new architecture. Moreover, we list the application scenarios using the proposed architecture.

In ultra-dense heterogeneous networks, the co-channel interference between small cells turns to be the major challenge to cell throughput improvement, especially for cell edge users. In this paper, we propose a distributed frequency resource allocation approach for interference cancellation, which allocates appropriate frequency resources when a small cell is switched on to reduce the co-channel interference to its neighboring small cells. This frequency resource pre - allocation aims at avoiding co-channel interference between small cells and improving users’throughput. The simulation results show that our proposed scheme can effectively reduce the co-channel interference and achieve considerable gains in users’ throughput.

The exponential growth of using wireless devices in recent years has motivated the exploration of the millimeter-wave (mmWave) frequency spectrum for multi-gigabit wireless communications. Recent advances in antenna technology, radio-frequency complementary metal-oxide semi-conductor (RF CMOS) process and high-speed baseband signal processing algorithms have promised the feasibility of millimeter-wave wireless communications. The multi-gigabit-per-second data rate of millimeter-wave wireless communication systems is leading to applications in many important scenarios, such as wireless personal area networks (WPAN), wireless personal area networks (WLAN), back-haul for cellular systems. The frequency bands include 28 GHz, 38 GHz, 45 GHz, 60 GHz, E-BAND, and even beyond 100 GHz.

The special issue aims to present some major achievements of the research and development in multi-gigabit millimeter-wave wireless communications. It includes four technical contributions from leading researchers in mmWave communications. The first paper entitled “Substrate-Integrated Waveguide-Based Monopulse Slot Antenna Arrays for 60 GHz Applications”, co-authored by ZHU, XUE and LIAO, presents the substrate-integrated waveguide (SIW)-based monopulse slot antenna arrays for the application of 60 GHz monopulse tracking systems. The second paper entitled “Millimeter Wave and THz Propagation Channel Modeling for High-Data Rate Railway Connectivity — Status and Open Challenges” is co-authored by Kürner, GUAN, Molisch, AI, HE, LI, TIAN, DOU and ZHONG. In this paper, the authors provide elementary discussions on bandwidth requirements of high-data rate railway connectivity, and highlight the open challenges in terms of wave propagation, static channel, and dynamic channel.

Co-authored by XU, MENG, MA and YEO, the third paper entitled “State of the Art in Passive Bandpass Filter Solutions for 60-GHz Communications”, reviews the state-of-the-art filter designs for 60-GHz applications. Design methodology, design technology, key performance parameters, similarities and differences, advantages and drawbacks, and future trends are explored and studied. The last (but not least) paper “Low-Power High-Efficiency Multi-Gigabit 60 GHz Transceiver Systems Routing in Vehicular Environments” is co-authored by Byeon and Park. It proposes low-power high-efficiency multi-gigabit 60 GHz transceiver systems for short-range communications. The antenna-in-package module with the transceiver demonstrates mobile-to-display 1080p Full-HD video transmission over a distance of 60 cm.

We would like to thank all the authors for choosing this special issue to publish their new research results and insights, all the reviewers for their valuable review comments which help to improve the technical quality and presentation of this special issue, and the editorial official of ZTE Communications for all the support and help during the editorial process of this special issue. We are sure this special issue will again be quite informative and a pleasure for you to browse through and read in depth.

The increasing requirements for bandwidth drive the 100G Ethernet into use as quickly as possible. The major technologies supporting 100G Ethernet interface include the physical layer channel convergence technology, multi-fiber channel and Wavelength Division Multiplexing (WDM ) technology. The key technology for high-speed optical devices at the interface requires a breakthrough. The demands driven by the increase of interface rate require better packet processing and storage, system switching, and backplane technology. In addition, in the network, the transport problem of the new interface should be solved, including defining transport standards and pushing the development of key transport technologies. As far as the cost and requirements are concerned, the commercial application of 100G Ethernet is viable in Metropolitan Area Networks (MANs ).