OPAL-RING
Koji ISHIBASHI Laboratory

Improving the Robustness of Wireless Communication to Ensure Uninterruptible Connections, Addressing the Problem of Finite Battery Power

Mobile phones and wireless communication equipment continue to advance year after year and have already achieved anytime/anywhere connectivity to an extent that might lead one to believe nothing more is needed. In reality, many issues remain to be solved, as revealed by the disaster caused by the Great East Japan Earthquake of 2011. The powerful earthquake destroyed wireless telecommunication base stations, rendering wireless communication devices useless in the affected areas. Furthermore, the lack of electrical power slowed restoration work. In this instance, functioning mobile phones would have saved countless additional lives. However, even if wireless connections had remained intact, the lack of electrical power would have made it impossible to charge the batteries required by telecommunication terminals. Dead batteries would have prevented communication, even if other factors had not.
Our laboratory engages in various research activities whose goal is to improve the robustness (that is, the systems or functions intended to shore up resistance to the effects of external factors) of wireless communication through revolutionary methods, safeguarding against communication interruptions and failures, maintaining connections at all times, initiating self-repairs in the event of communication problems, and eliminating the problem of finite battery power.

Data Communication Through Wireless Distributed Networks Using a Bucket Relay System

Extensive Knowledge of Information Theory and Wireless Communication Technologies, Capacity to Achieve Practical Specifications

Assistant Professor Ishibashi’s previous research activities ranged widely, from information theory to programming, device circuit designs, microprocessors, sensor networks, and electric power optimization. His extensive research experience provides familiarity with both theory and technology, a key advantage offered by our laboratory.
Many researchers active in the areas of information theory and communication systems concentrate on constructing original theories based on many idealized assumptions, in accordance with the mathematical model formulated by Claude Shannon. In contrast, researchers active in the area of devices and systems focus on optimizing electrical circuits. The field of communications is comprised of multiple layers; few researchers are capable of interconnecting these layers based on an understanding of the overall system. The achievements of Assistant Professor Ishibashi stem from research from the perspectives of both theory and technology.

Conserving Electric Power Based on a Wireless Distributed Network and Dynamic Cooperative System

In ordinary relay communications, direct data transfers can result in communication failures. To improve reliability, data is sent to terminals other than those used for the bucket relay, allowing retransmission from another terminal in case of transmission failures. However, since this method involves sending the same data several times, it has the drawback of relatively lengthy communication times.
In response, Assistant Professor Ishibashi is currently exploring a method called dynamic cooperation, based on an ingeniously designed error correction code. In this system, a relay terminal reconstructs the transmitted data during data transmission. As soon as the relay terminal successfully receives the data, it dynamically superimposes auxiliary information onto the signal from the transmitting terminal, then sends the data. The receiving terminal receives the correct data by combining the auxiliary information from two signals.
Dynamic superimposition of auxiliary information dramatically improves communication efficiency and ensures stable transmission of data by the bucket relay method. In general, reliable transmission of data over long distances requires powerful radio waves. In contrast, this system allows reliable communication even with weak radio waves. An additional benefit of this approach is lower power consumption. The results of Assistant Professor Ishibashi’s research are expected to lead to new possibilities in relay transmission.

Energy Salvage Mechanism and Energy Harvesting Technologies

No matter how much we reduce the electric power required for communications, the batteries that power our communication devices have finite capacity and eventually run out. Our laboratory pursues research on energy salvage mechanisms that will allow terminal devices to collect unnecessary electromagnetic waves and reuse them as electric power. Alongside this effort, we are working on energy harvesting technologies capable of converting solar light, ambient light, radiant heat, vibrations, and radio waves into electric power. Ultimately, our goal is to create a communication environment that eliminates the problem of limited battery power.

A Network of Contacts Around the World

After graduating from the University of Electro-Communications, Koji Ishibashi held positions at various universities, building an extensive personal network of contacts in Japan and overseas. The individuals with whom he maintains contact include colleagues at Harvard University. This global network of contacts is one of our laboratory’s strengths.

Making Anytime/Anywhere Connectivity for Mobile Phones and Wireless Communication Equipment a Cornerstone of the Social Infrastructure

Eliminating the Roadblock of Limited Battery Power and Achieving Wireless Power Supply to Mobile Phones

Eliminating the problem of limited battery power for communication terminals is another research topic addressed by our laboratory. Although mobile phones are wireless devices, they still require power supply cables to charge their batteries. Understood literally, wireless means cordless. Our research focuses on ways to circumvent the limitations imposed by finite battery power by supplying electric power wirelessly so that mobile phones will truly be cable-free.