1. Institute of Basic Science, Korea University, 5-1, Anam-Dong, Sungbuk-Gu, Seoul 136-701, Korea
2. R&D First Team, ECO Corporation, Sunyang Bldg. 49, Nonhyun-Dong, Gangnam-Gu, Seoul 135-010, Korea
3. Dept. of Computer Science and Engineering, Korea University, 5-1, Anam-Dong, Sungbuk-Gu, Seoul 136-701, Korea
4. School of Computer & Communication Engineering, Wonkwang University, 344-2, Shinyong-Dong, Iksan, Cheonbuk 570-749, Korea