1. Department of Computer and Communication Engineering, Chungbuk National University, 52 Naesudong-ro, Chengju-si, Chungbuk 361-763, Republic of Korea
2. 2nd R&D Institute, Agency for Defense Development, P.O. Box 132, Seoul 138-600, Republic of Korea
3. Department of Electronic Commerce, Pai Chai University, 155-40 Baejae-ro, Seo-Gu, Daejeon 302-735, Republic of Korea