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from the active period can go into sleep during the sleep period, reduction of power consumption can be realized.2.2Multi-hop communications on PAN topologyFigure 3 shows an operating example which implements the multi-hop communications by using the low-energy MAC method described in the previous section on the topology of the personal area network (PAN) which is the premise for SUN. PAN is the radio device network specied in the IEEE 802.15.4 standard [10], and is composed of a radio device called a PAN coordinator, which is rst acti-vated to declare PAN establishment, and a radio device which executes association, a subscribing procedure to PAN. Paying attention to the relationship between the radio device which executes association and the radio device which receives association, we can nd the tree-structured PAN topology whose root is the PAN coordinator. We propose a multi-hop communication conguration which collects data from other devices using this tree structure to the PAN coordinator as a collection station (CS). In Figure 3, it can be conrmed that when the D3 or D4 sends the data frames to D1, the sending conforms to the super-frame specied in D1, and when D1 sends them to CS, the sending conforms to the superframe specied in CS.Figure 4 shows the estimated result of battery life when assuming the low-energy multihop communications as referred to above. e assumed battery capacity is three AA batteries. e calculated result shows that if the beacon interval is 80 seconds, data length is 100 octets, and the data generation interval is one minute or so, the battery life can be expected to be 10 years or more.2.3Study of low-latency communications for control, etc.As mentioned in the previous subsection, the basic principle of low-energy action is the intermittent standby by the introduction of a sleep period. On the other hand, it is believed that the operation modes for the wireless grid can include the control action which executes the data transmission from the collection station to each device by assuming an actuator, etc. as the device, in addition to the sensing action which mainly executes data transmission from each device to a collection station by assuming a sensor, etc. as the device. It is expected that in such control action, delay inevitably occasioned by the introduction of the sleep period sometimes becomes serious. For this reason, this research and development has studied the pattern to implement low-latency control action in parallel with low-energy sensing action.Figure 5 shows the concept of low-latency communica-tions. For PAN, this study denes the device connecting to the actuator, etc. above as a control target device, and the FiF4　Estimated battery lifeFiF5　Concept of low-latency communications(a) Conventional action(b) Low-latency action272-4 Research and Development on the Low-Energy Wireless Grid Technologies for Agricultural and Aquacultural Sensings