1. a Comtec Systems Co., Ltd. , 779–10 Daelim3‐Dong, Youngdungpo‐Ku, Seoul , 150–816 , Korea
2. b Samsung Electronics Co., Ltd. , San #24 Nongseo‐Ri, Kiheung‐Eup, Yongin‐City , Kyunggi‐Do , 449–711 , Korea
3. c Department of Electrical Engineering & Computer Science , KAIST , 373–1 Kusong‐Dong, Yusong‐Ku , Daijon , 305–701 , Korea Phone: Fax: E-mail: