1. Department of Computer Engineering, Hoseo University, 165 Sechul-ri, Baebang-myun, Asan, Chungnam 336-795, Republic of Korea
2. Department of Electrical Engineering and Computer Science, Northwestern University, Technological Institute, 2145 Sheridan Road, Evanston, IL 60208, USA
3. Department of Computer Engineering, Hansung University, 389 Samseon-dong 2-ga, Seongbuk-gu, Seoul 136-792, Republic of Korea