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due to cuto, the establishment of a low-damping alterna-tive path using multistep relay can resolve the radio blind spot. Consequently, the multi-hop technology can extend the service area.NICT works in research and development regarding the establishment of low-energy multi-hop communication technology with the goal of the eective implementation of SUN. As shown in Fig. 1, SUN is expected to be eective for wide uses for not only smart meter systems but also for sensor networks, etc. Here we describe the research and development regarding the low-energy multi-hop com-munication technology and an application demonstration to shery and agriculture.2Overview of the low-energy multi-hop communication technology2.1Overview of the low-energy MAC methodFigure 2 shows an operating example of the low-energy MAC method [3]–[7] applied in this research and develop-ment. is method was proposed by NICT, and uses the low-energy superframe structure dened in IEEE 802.15.4e [8][9]. e superframe is a time period forming the basis of the Time Division Multiple Access (TDMA) control, and is specied by a cyclic beacon signal. e beacon interval (BI), a basic time unit, is divided into the active period (AP) — sending and receiving, or standby — and the sleep period (SP) which turns o the power and does not execute the sending and receiving, and the active period is oper-ated as the real communication period. On the other hand, the sleep period allows each device to go into sleep. For the low-energy action, the beacon signal is not sent to every superframe, and essentially, is sent only if temporal synchronization is required. In addition, as shown in the gure, as the active period is sometimes shorter than the data frame, the end of the data frame shall not be limited within the active period and should be before the starting point of the next superframe. As a result, reduction of the active period becomes possible, regardless of the data frame length. In other words, because the reception status for the start of the standby and the sending and receiving of the data frame at each terminal is executed only in the active period and the terminals other than the terminals involved in the sending and receiving of the data frame continuing FiF1　Overview of smart utility network FiF2　Operating example of low-energy MAC methodFiF3　Operating example of multihop communications2 Terrestrial Communication Technology Research and Development26　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 2 (2017)