Dr. Tadao Ishibashi Senior Research Engineer, Supervisor NTT System Electronics Laboratories 3-1, Morinosato Wakamiya, Atsugi-Shi Kanagawa Pref., 243-01 Japan Tel.: +81 462 40 2888 Fax: +81 462 40 4306 e-mail: ishi@aecl.ntt.jp