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1Introductione National Institute of Information and Communications Technology (NICT) carries out research and development regarding the ecient use and social development of a wireless grid structure composed of a spidery (grid) connection topology by multiple wireless terminals that are expected to have an eect on the IoT eld in which demand has recently increased. One of the typical examples of the application of the wireless grid structure is the Smart Utility Network (SUN) which is formed by a smart meter equipped with a radio device, and which implements automatic meter reading, control, etc. [1][2]. Figure 1 shows an overview of SUN. e main technical problems for SUN are considered to be the two below.(1) Low-energy technology which assumes battery op-eration(2) Multi-hop technology which extends the service areaFor item (1), the technology becomes of particular importance when, for gas and water meters, the power supply from outside the meter by wire, etc. is not easy, and assuming the operation of the meter and SUN radio by a built-in battery. It goes without saying that the battery changing cost due to the increase of the battery changing frequency due to battery drain is a problem that may re-verse the premise of the SUN system. From the standpoint of meter operation, in general, continual operation for 10 years or more without changing the battery is regarded as a goal.Next, for item (2), as shown in Fig. 1, when the meter is placed far from a collection station or the meter is placed in a cuto environment, such as in a housing complex, damping of the signal due to the distance and cuto and occurs, and direct communications alone cannot be imple-mented in the required service area, so the technology collects all meter reading data by executing a multistep relay. For the damping due to distance, multistep relay by introducing multi-hop technology can increase the reach-able radio distance in a linear manner, and for the damping 2-4 Research and Development on the Low-Energy Wireless Grid Technologies for Agricultural and Aquacultural SensingsFumihide KOJIMAThis article reports on the R&D on the low-energy operation that is defined as one of capabilities for the wireless-grid systems where several radio devices are connected in the grid-like topology. This R&D activity includes a study on low-energy multi-hop transmission technology that realizes relay transmissions among devices by holding a low-energy MAC scheme with effective sleep-periods. In the assumed wireless Personal Area Network (PAN) employs the low-energy superframe structure that is defined in the IEEE 802.15.4e global standard and deploys intermittent active periods on every radio devices with time synchronization, thereby achieves power consumption reduction entire the PAN and establishes a suitable tree-shaped multi-hop communication topology. It is confirmed that the assumed low-energy operation theoretically enables more than 20 years operation with only three AA batteries. We have successfully developed low-energy radio devices with the proposed low-energy multi-hop communication capability and confirmed its suitable performances via several proof tests. As an example of effective utilities of such radio devices, we have successfully applied the radio device equipped sensor-buoys to the periodical sensing of water-temperature and salinity conditions in the Mozuku seaweed farm. Besides such an aquacultural application, we have further studied on the radio device application to the agricultural water management application and confirmed that the developed radio devices have effectively worked for both low-energy sensing operations such as rice farm water level monitoring and low-latency control operations such as water pump control.252 Terrestrial Communication Technology Research and Development