Soft Hardware for Future Wireless Communications

Hitoshi Ishikuro (Associate Professor, Department of Electronics and Electrical Engineering)

Recently, we often hear the word "ubiquitous." It refers to an environment where we can connect to a network and exchange information anytime, anywhere, and it goes without saying that wireless communication technology is the foundation of this. Next-generation mobile phones will be able to transmit 1 billion bits of information per second (1 Gbps), allowing for the stress-free exchange of large-volume video data.

As you may have learned in the "waves" section of high school physics, waves have variables such as frequency, phase, and amplitude. It is no exaggeration to say that the history of wireless communication is the history of developing technologies to freely manipulate the frequency, phase, and amplitude of radio waves—a type of wave—to transmit information. How to handle these variables for optimal communication varies greatly depending on the situation (e.g., indoors, outdoors, during high-speed movement). To adapt to various situations, mobile terminals are required to automatically assess their surroundings and switch their hardware functions flexibly and smartly.

Various technologies of this kind are being researched, and one of the most interesting is called a smart antenna. When two or more waves are superimposed, a phenomenon called interference occurs, where they strengthen or weaken each other depending on the location. Using this principle, it is possible to send radio waves only to the intended recipient (Figs. 1 and 2). Since there is no need to send radio waves in unnecessary directions, precious radio wave resources can be used effectively. If the phase of the waves can be adjusted with an electronic circuit, the direction and intensity of the radio waves can be switched freely and at high speed without mechanically changing the shape or orientation of the antenna.

"Soft hardware," which can freely change its own functions, has become a hot research topic in this field, but until now, it has required extremely large and expensive equipment. For example, in the case of the smart antenna mentioned earlier, it is necessary to control the phase of the wave with an accuracy of a few degrees, or in terms of time, one hundred-billionth of a second, which is not an easy task. However, recent advances in large-scale integration (LSI) technology have made it possible to place hundreds of millions of ultra-high-speed transistors on a silicon chip a few millimeters square, enabling the complex signal manipulation described above.

Just as the rapid improvement in PC performance has allowed individual programmers to create amazing software, it is now possible to realize surprisingly complex and high-functionality circuits on a small silicon chip if you have the ideas (Fig. 3). We are conducting daily research toward the realization of an LSI equipped with soft hardware (circuits) that can handle all types of wireless communication on a single chip in the future.

Fig. 1: Directional control of radio waves by a smart antenna (beam steering)

Fig. 2: Simulation of directional control of radio waves

Fig. 3: Prototype LSI silicon wafer (left) and a magnified photo of the circuit section (right)