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OKI Develops Japan’s First 920MHz Frequency Band Wireless Multi-hop Communication System for Smart Communities


TOKYO - OKI today announced that it has succeeded in the development of Japan’s first wireless multi-hop communication system for the new 920 MHz frequency band(*1) which is scheduled to open by the Ministry of Internal Affairs and Communications in July 2012. The 920 MHz band offers high signal propagation and considerable promise for wireless multi-hop communication(*2) technologies ideally suited for use in smart communities, smart houses and smart meters. (*3)
Smart grids that use information communication technologies for energy management such as electricity have attracted significant interest, and studies continue on smart communities capable of deploying such management control and smart houses that make effective use of green energy.
“Making smart communities and smart houses a reality requires a communications infrastructure to transmit data, such as electricity control data. The communications infrastructure will require home networks (Figure 2) that connect home appliances and electrical power equipment within the home or office, and field area networks (Figure 1) that connect devices such as smart meters between outside buildings,” says Takeshi Kamijoh, General Manager of Research and Development Center at OKI. “Wireless multi-hop communications are expected to make such infrastructures possible. Electrical power equipment such as smart taps and smart meters are often installed in locations with poor signal access, underscoring the significance of the 920 MHz band with its high signal propagation compared with 2.4 GHz which broke communications.”
920MHz Wireless Multi-hop Communication Technology Application Domain
OKI has developed an IEEE 802.15.4(*4)-compliant wireless multi-hop communications system to accommodate conditions of use for the new 920 MHz frequency band currently being deliberated on by the Ministry of Internal Affairs and Communications, and OKI evaluated performance using an acquired experimental transmitter. The testing confirmed that communication is possible over 10km when transmission output of 250mW, the specified maximum. The testing also confirmed direct communications in urban locations among many obstacles such as buildings at a transmission output of 70mW within an area of approximately 150m in radius.
Moving forward, OKI will play a major role in promoting widespread use of smart communities, smart houses and smart meters based on 920 MHz wireless multi-hop technology. By applying this technology to a wide range of new services, OKI will also try to realize a society in which people feel more comfortable, safer, and secure. In addition to incorporating this technology into commercial products, OKI will draft plans for the ZigBee(*4) standards that support 920 MHz for smart houses to familiarize ZigBee standards which is recognized internationally, and will also continue working to strengthen interconnectivity for home appliances, electrical power equipment, and home gateways.
The achievements to date will be presented at the Institute of Electronics, Information and Communication Engineers Society Conference to be held at Hokkaido University on September 14.
Features of the 920 MHz band wireless multi-hop communication system developed by OKI
This wireless multi-hop communication technology uses the 920 MHz frequency band with its high signal propagation, enabling networks with wider and more systematic coverage and stable communication infrastructures that do not depend on installation location.

  • Large scale

The technology achieves scalability to accommodate more wireless devices by reducing controlled traffic for route searching and by establishing retransmission procedures. By use of this technology, it will be possible to establish large-scale multi-hop networks consisting of thousands of wireless devices per base station with smart meters. Fewer base stations are required, reducing overall system setup costs. OKI has already evaluated experimental systems with up to 100 devices using the 950 MHz band, both indoors and outdoors. The results indicate these systems are expected to accommodate networks of several thousand devices.

  • High reliability

The system provides improved connectivity between wireless devices by using specially-developed retransmission and dynamic route controls to handle fluctuations in adjacent wireless links caused by obstructions such as vehicles. The system is also resistant to base station faults and line disturbances between base stations and the hub, thanks to functions that allow individual wireless devices to switch independently to different base stations. It also allows easy base station maintenance without shutting down.

  • Energy savings 

To this point, energy savings for end-point wireless devices have been achieved via ZigBee by continuously operating routers with relay functions. It is now possible to switch routers to sleep mode using energy-saving functions complying with IEEE 802.15.4e. This eliminates the need to install power supplies for routers and increases the overall energy savings achieved. Adding functions to automatically adjust sleep mode timing in conjunction with data flows will minimize transmission delays while maintaining energy savings. The Ministry of Internal Affairs and Communications Network Integrated Control System Standardization Promotion project has been seeking to standardize IEEE 802.15.4e. In this project, tests were performed in March 2011 of various energy-saving functions using an IEEE 802.15.4e-compliant test bed.

  • Simple installation 

Automated route searching functions allow easy network construction based on automated and independent connections to temporary base stations and wireless devices. This configuration also makes it possible to provide low-cost temporary networks after disasters. Wireless multi-hop communications are subject to network instability due to the lack of relay routes in configurations with a low density of installed wireless devices—for example, on the initial rollout of smart meters or smart house applications. However, stable network operations can be achieved from the start by adding a function that automatically adjusts transmission output to suit the distance separating devices. The relaxation of transmission output limits following the shift to the 920 MHz band allowed higher output, enabling wireless multi-hop communications even in locations with considerable distance separating devices.

  • *1 :920 MHz frequency band

Encompassing frequencies between 915.9 MHz and 929.7 MHz in Japan, this frequency band is widely used outside Japan for applications such as smart meters, due to high signal propagation compared to the 2.4 GHz band generally used for sensor networks. Not only do signals go farther; they also circumvent obstructions, making the band ideal for use in locations with numerous obstructions, such as hospitals or factories, or outdoors.
While the 950 MHz band has been in use in Japan since the band was institutionalized in 2008, the shift to the 920 MHz band is expected to stimulate the market through international partnerships, since the same frequency band is used in the United States and Asia. The 920 MHz band also permits higher transmission output (20 mW or 250 mW) than the previous 10 mW limit.

  • *2 :Wireless multi-hop communication

Wireless multi-hop communication refers to data transmission involving other wireless devices by a “bucket brigade” process. It is widely used in sensor networks due to its capacity to function without communications infrastructure elements such as base stations.

  • *3 :Smart communities, smart houses, smart meters

Smart communities and smart houses are parts of an initiative being promoted by the Ministry of Economy, Trade and Industry to efficiently manage regional and domestic energy consumption and make our society more comfortable by expanding the use of reusable energy while minimizing the impact on Japan’s stable power transmission network.
Smart houses monitor electricity consumption using distribution boards and smart taps (power outlets with communication functioning) to make domestic energy consumption more visible and thereby encourage power savings. Additionally, they are expected to include systems that reduce power consumption by regulating electrical appliances during peak power demand periods and to store surplus power from solar panels in batteries or electric vehicles for use at night.
Smart meter is a general term for next-generation meters incorporating communication functions intended for use in electricity, gas, and water meters. They range widely—from devices that have a single function (to take meter readings automatically) to devices used to control energy consumption. Power and gas utility companies are currently proceeding with demonstration tests ahead of the introduction of smart meters. The Ministry of Economy, Trade and Industry has implemented a number of related initiatives, including the Study Group on the Smart Meter Scheme, to promote the early adoption of smart meters.

  • *4 :ZigBee, IEEE 802.15.4

Wireless multi-hop communications such as sensor networks generally comply with IEEE 802.15.4 international standards for wireless communications and ZigBee for network. Implemented as a standard in 2009 following deliberations headed mainly by OKI, IEEE 802.15.4 includes a physical layer extension known as IEEE 802.15.4d that supports the Japanese 950 MHz band. IEEE 802.15.4g, the physical layer extension standard for smart meters, is currently in the final phase of deliberations ahead of standardization scheduled for December 2011. A MAC layer extension standard for industry use, under deliberation as IEEE 802.15.4e, is also scheduled to be implemented in December 2011. It will add features such as router energy saving functions.
The ZigBee Smart Energy Profile is widely used in the smart house market. ZigBee SIG-J for the 920 MHz band is also being deliberated as an alternative.
About OKI Electric Industry (OKI)
Founded in 1881, OKI Electric Industry is Japan’s leading telecommunications manufacturer. Headquartered in Tokyo, Japan, OKI provides top-quality products, technologies, and solutions to customers through its info-telecom systems and printer operations. Its various business divisions function synergistically to bring to market exciting new products and technologies that meet a wide range of customer needs in various sectors. Visit OKI’s global website at
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