1. a Information Technology Laboratory , LG Electronics Research Center , 16 Woomyeon-Dong, Seocho-Gu, Seoul 137-140, Korea Phone: Fax: E-mail:
2. b Department of Electrical Engineering , Korea Advanced Institute of Science and Technology , 373-1 Kusong-dong, Yusong-ku, Taejeon, 305–701, Korea Phone: Fax: E-mail: