1. Research Institute of Electrical Communication, Tohoku University, Aoba-ku, Sendai, Japankmat@riec.tohoku.ac.jphttp://www.riec.tohoku.ac.jp/~kmat
2. Research Institute of Electrical Communication, Tohoku University, Aoba-ku, Sendai, Japanshioiri@riec.tohoku.ac.jphttp://www.riec.tohoku.ac.jp/~shioiri