1. Department of Electronic Systems Engineering The University of Shiga Prefecture 2500 Hassaka‐cho, Hikone 522‐8533 Japan
2. Graduate School of Systems and Information Engineering, Department of Engineering Mechanics and Energy University of Tsukuba 1‐1‐1 Tennoudai, Tsukuba 305‐8573 Japan
3. Toshiba Corporation, 2‐1 Ukishima‐cho Kawasaki‐ku, Kawasaki 210‐0862 Japan