OKI reported that OKI successfully developed the wireless multi-hop communication (2) system in the 920MHz band (1) for the first time in Japan. The Ministry of Internal Affairs and Communications plans to open the 920MHz frequency band in July 2012. This band has high radio wave reachability and is expected to become the most suitable frequency band for wireless multi-hop communication in smart communities, smart houses, and smart meters (3).
The wireless multi-hop communication system developed by OKI conforms to the IEEE802.15.4 (4) standard in the 920MHz band under consideration by the Ministry of Internal Affairs and Communications of Japan, and a verification experiment was carried out after obtaining permission from the Experiment Bureau. The results show that with the maximum specified 250mW transmission, the communication distance can reach 10km. Even in urban streets with many obstacles such as buildings, 70mW transmission can achieve direct communication with a radius of about 150m.
In the future, OKI will continue to contribute to the popularization of smart communities, smart houses, and smart meters based on the wireless multi-hop technology in the 920MHz band. And through the flexible application of this technology to disaster prevention, patrol, medical, nursing and other new services, we strive to achieve a more comfortable, safe and secure society. In the future, efforts will be made to realize productization based on this technology. At the same time, in order to spread the internationally popular ZigBee (4) standard in Japan, the ZigBee standard supporting the 920MHz frequency band for smart homes will be developed and continue to promote home appliances and electricity Connected activities such as devices and home gateways.
Features of 920MHz band wireless multi-hop communication system developed by OKI
The wireless multi-hop communication technology can construct a large-scale network covering all corners by using the 920MHz frequency band with high radio wave reachability, and can achieve stable communication infrastructure without selecting a location.
1) Large scale
The flow control caused by path exploration is reduced, and by studying the design of the retransmission structure, the scalability of the number of wireless devices is realized. In this way, a large-scale wireless multi-hop network composed of thousands of wireless devices such as smart meters can be constructed. As the number of base stations decreases, the overall cost of the system can be reduced. OKI already has the performance of carrying out evaluation and verification of indoor and outdoor use of 100 sets of equipment in the 950MHz frequency band, and it is expected that this system can be built to expand to thousands of networks.
2) High reliability
In response to changes in wireless network connections in a small area caused by obstacles such as vehicles, OKI has implemented unique retransmission control and dynamic path control to improve connectivity between wireless devices. Moreover, the function of automatically switching the base station by each wireless device can resist the failure of the base station or the line failure between the base station and the center, and the network can continue to operate without interruption even during the maintenance of the base station, so a network that is easy to maintain can be constructed.
3) Power saving
So far, ZigBee has been used, and the uninterrupted operation of the router with the relay function has realized the energy saving of the terminal wireless device. The IEEE802.15.4e power-saving feature allows the router to sleep. Therefore, without the power engineering of the router, the overall power saving effect of the system will also be improved. And by adding the function of automatically adjusting the sleep time according to the data flow, not only can maintain the power saving effect but also ensure low-latency transmission. In addition, the standardization activities of IEEE802.15.4e achieved results from the "Network Integrated Control System Standardization Promotion Business" implemented by the Ministry of Internal Affairs and Communications of Japan. In March 2011, a test bench based on the IEEE802.15.4e standard was constructed and the power-saving function was implemented Verification experiment.
4) Simple setup
Using the automatic path construction function, you can automatically connect to a temporarily installed base station or wireless device to easily build a network. Therefore, it is possible to provide the network temporarily set up in the event of a disaster at low cost. In addition, in wireless multi-hop communication, if the installation density of wireless devices in the initial stage of smart meters and smart houses is too low, there will be problems of insufficient relay paths and unstable networks. However, after the function of automatically adjusting the transmission output according to the set interval has been developed, stable network operation can be achieved from the initial stage of adoption. Especially when switching to the 920MHz frequency band this time, because the upper limit of the transmission output is loose, higher output can be used, so wireless multi-hop communication can be used even in places with wide intervals.
Terminology
(1) 920MHz band
The frequency band 915.9 ～ 929.7MHz is used in Japan. Compared with the 2.4GHz frequency band mainly used for sensor networks, the radio wave has high reachability. Therefore, the same frequency band overseas can also be widely used in smart instruments. Not only can it reach a long distance, but it can also be reached roundabout even if there are obstacles. It is suitable for factories and hospitals and other places with many obstacles and outdoor use. Japan has been using the 950MHz frequency band established in 2008. After converting to the 920MHz frequency band, it can use the same frequency band as the United States and Asia. It is expected to activate the market through international cooperation. And the transmission output can also be expanded from the previous 10mW to 20mW or even 250mW.
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