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1IntroductionFor the h generation mobile communication system (5G), system requirements include enhanced mobile broad-band (eMBB), ultra-reliable and low latency communica-tions (URLLC), and massive machine-type communications (mMTC), and R&D for realizing 5G has been promoted in countries all around the world. Especially, as a point of dierence with conventional mobile communication sys-tems, there are expectations that 5G will cover IoT ser-vices, and in addition to massive numbers of IoT devices as user equipment (UE) being connected to base stations (BS), it is projected that a wide range of diverse services will be on oer [1].Along with massive connections, there are also expecta-tions over the provision of services that require low la-tency, such as autonomous driving, and there will be a need for technology that can realize low latency while concur-rently realizing an increase in the number of UE that can be connected to a BS on the same time and frequency resource. In the IoT environment, which has vast numbers of devices such as sensors connected to it, radio access technologies without iterative procedures such as radio resource scheduling requests (SR) and the corresponding grants will make multiple connections and low latency possible; but, because signal collision probability increases as the number of connected UE increases, the ecient detection of signal collision during times of multiple con-nections becomes an issue.In order to solve this issue, we are involved in R&D related to radio access technologies that are equipped with (1) technology that identies transmitting terminals and establishes both multiple connections and low latency and (2) technology that suppresses or eliminates interference. With existing radio access technologies, only one terminal can be connected at the same time on the same frequency to each individual antenna of a BS or access point. In contrast to this, simultaneous connection with multiple terminals can be realized with this radio access technology.2Development of the Radio Access TechnologyFigure 1 shows an outline of radio access technology that realizes simultaneous connectivity and low latency. With this radio access technology, frequency usage e-ciency is improved by having multiple UEs share the same frequency at the same time, and latency is reduced by employing data transmission without grant, which mini-mizes the scheduling requests before data transmission when UE has data to be sent to BS.In order to realize this radio access technology, because multiple UEs will be sharing the same frequency at the same time, there will be a need for (1) technology that can identify the UEs that are connected at the same time and (2) technology that suppresses or eliminates interference 2-2 Radio Access Technologies for Massive Machine-Type CommunicationsKenichi TAKIZAWA, Masafumi MORIYAMA, Masayuki OODO, Changwoo PYO, Hayato TEZUKA, Homare MURAKAMI, Kentaro ISHIZU, and Fumihide KOJIMAIn the IoT era, a radio access technology collects small-size messages sending from user equipment (UE) to base station (BS) is crucial in frequency efficiency viewpoint, especially in massive machine-type communications (mMTC). Some part of mMTC application fields like connected cars or drones needs a radio access technology that provides low latency. We have been engaging to develop a radio access technology that covers the requirements on both efficiency in frequency usage and low latency, by introducing a radio frame structure with resource blocks (RBs) shared by multiple UEs without grant from BS. We have conducted performance evaluation through link level simulations towards realizing a radio access technology that RBs are shared by 5 UEs per one BS antenna with latency of less than 5 ms.132 Terrestrial Communication Technology Research and Development