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1IntroductionWith the rapid increase of wireless applications, typi-cally in mobile phones and wireless LAN, frequency re-source depletion is a serious issue. As allocation of wide signal bandwidth is required for future high-speed com-munications, utilization of millimeter-wave and terahertz-waves is under considering. Conventionally, these frequency bands have been considered unsuitable for mobile communication use because the optical nature of the waves (strong tendency of straightness) becomes more apparent as the frequency goes up. However, owing to many innovations in recent wireless technology, it is ex-pected that millimeter and terahertz waves will open new possibilities in mobile communications. In accordance with this trend, Agenda Items (AI) related to these frequency bands will be discussed in World Radiocommunication Conference 2019 (WRC-19)[1], for example: identication of candidate frequency bands in the range 24.25–86 GHz to be added to the International Mobile Telecommunications (IMT) band; and frequency band identication in the range 275–450 GHz to be used for land-mobile and xed ser-vices applications. For further investigation into the practi-cal use of these frequency ranges, the propagation properties need to be characterized for link budget design of wireless systems and interference evaluation of fre-quency sharing. In this report, we describe the current status of millimeter and terahertz wave propagation re-search now underway in NICT.2Research on millimeter wave propagationAs a part of the research on millimeter-wave wireless applications in the wireless systems laboratory of NICT, the characterization of propagation properties is currently fo-cusing on two areas: railway radiocommunication systems between train and trackside, and mobile communications in urban environment. ese two areas relate to AI 1.11 and AI 1.13 will be discussed in WRC-19: the former in-tends to consider a possible global or regional harmonized frequency band to support railway radiocommunication systems between train and trackside, and the latter intends to identify frequency bands for future development of IMT. is section describes key points of propagation character-istics and the development of propagation models for these areas.2.1Propagation characteristics for railway radiocommunication systems between train and trackside [2]In preparation for the discussions held in WRC-19, plans toward establishing a worldwide or regional harmo-nized frequency identication, in frequency bands which are already allocated in mobile services, are under review in ITU-R (ITU Radiocommunication sector). In Japan, studies of the millimeter wave range for railway radiocom-munication started in around 1980, and in recent years, attention has focused on the use of millimeter wave in the 40 and 90 GHz bands between train and trackside radio-communication. e use of the 90 GHz band for this purpose is attracting attention relatively recently in con-nection with AI 1.11. In the research and development toward harmonized use, characterization of propagation properties and interference evaluation are actively under-way in view of the fact that a wide portion of frequencies in the 90 GHz range has already been allocated for mobile services. NICT has conducted, in collaboration with ali-2-3 Study on Propagation Model for Advanced Utilization of Millimeter- and Terahertz-WavesHirokazu SAWADA, Kentaro ISHIZU, and Fumihide KOJIMA To realize high speed wireless communication systems using millimeter-wave and terahertz-wave are expecting, and a study of radio-wave propagation is on-going for introduction of these future radio systems. In this report, the recent results of radio propagation research on millimeter-wave and terahertz-wave bands are described.192 Terrestrial Communication Technology Research and Development