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e use of information infrastructure has become an essential part of our daily lives today. Most of this infra-structure is accessed using wireless technology. Recent years have seen remarkable advances in wireless network technology and the world of mobile communications is in the process of evolving from fourth-generation (4G) tech-nologies such as LTE to h-generation (5G) systems. Unlike 3G with CDMA and 4G with LTE/WiMAX, the term 5G does not indicate any particular technology, de-scribing instead a new communications environment cre-ated by a diverse array of technologies that meet a wide range of user needs, so the scope of research and develop-ment is extremely broad.On the other hand, in the realm of information use, IoT is undergoing rapid advances, with wireless technology essential to both the collection of sensing data and the control of device actions (actuation). In IoT, sensing and actuation in locations without a human presence is of great signicance, so not only terrestrial wireless, but also satel-lite communications covering marine areas and airspace, and communication systems that use unmanned aerial vehicles (UAVs) and drones are vital.Since the previous medium to long-term plan period, NICT’s Wireless Networks Research Center has been conducting research and development focused on the wire-less network technology and ultra-high-speed satellite communications technology that will need to be applied in 5G and IoT systems. is special issue presents the out-comes of that work.Section 2 focuses mainly on terrestrial wireless network technology. e articles summarize the outcomes of re-search and development in the realm of the exible archi-tecture and spectrum sharing technologies required for 5G systems, massive device connectivity technology, and mil-limeter- and terahertz-wave transmission models. is section also describes the results of research and develop-ment focused on technologies for building large-scale mesh networks, which are eective for building sensing systems and power-saving grid communications systems for use in sensing in the agriculture and sheries industries, where IoT oers promising possibilities, and also wireless com-munication stabilization technologies that can be eective in manufacturing sites. Moreover, it includes the ndings from research into terminal-to-terminal communication systems for expanding wireless network usage environ-ments; wireless technologies for use in extreme environ-ments, such as underwater and in deep space; and wireless technologies that use small UAVs.Section 3 summarizes the outcomes of an empirical study involving various demonstration experiments using the Wideband InterNetworking engineering test and Demonstration Satellite (WINDS). WINDS is a demonstra-tion satellite developed in partnership with the Japan Aerospace Exploration Agency (JAXA) to facilitate ultra-high-speed satellite communications. It was launched in February 2008 and continues to be used for various ex-periments today. WINDS has succeeded in achieving a transmission speed of 3.2 Gbps, the world’s fastest in xed satellite communications. It is equipped with world-class ultra-high-speed satellite communications capabilities, with a 50-cm-diameter antenna that enables it to receive signals at speeds of up to 155 Mbps and on-board switch-ing capabilities of up to 455 Mbps. For details of the satel-lite and network design and development, please see Journal of NICT vol.53 no.4.As well as providing an overview of the WINDS fun-damental experiments, this special issue reports on the results of a diverse array of other experiments conducted using WINDS in the areas of communication systems, trialing of applications, and on-board equipment integrity checks. ese include rain attenuation compensation ex-periments; disaster countermeasures experiments; terres-trial network connection experiments; orthogonal frequency-division multiplexing modulation transmission experiments; ultra-high-denition television transmission experiments; APAA integrity check experiments; aircra communications experiments; Ka-band multi-level modu-lated signal transmission experiments; marine communica-1 Introduction: Special Issue on Terrestrial Communica-tion Technology and Ultra-High-Speed Satellite Com-munications TechnologyNaoto KADOWAKI11 Introduction: Special Issue on Terrestrial Communication Technology and Ultra-High-Speed Satellite Communications Technology