1. Department of Electrical Electronics and Information Engineering Nagaoka University of Technology, 1603–1, Kamitomioka‐machi Nagaoka Niigata 940–2188 Japan
2. Department of Electrical and Electronic Engineering of Faculty of Engineering Shizuoka University, 3‐5‐1, Johoku, Naka‐ku Hamamatsu Shizuoka 432‐8561 Japan
3. Electrical and Electronics Engineering Program Tokyo Metropolitan College of Industrial Technology, 1‐10‐40 Higashi‐Ohi, Shinagawa‐ku Tokyo 140–0011 Japan