1. Department of Electronic Engineering, Sogang University, 1 Sinsu-dong, Mapo-gu, Seoul 121-742, Republic of Korea
2. Department of Computer Science, Inha Technical College, 100 Inha-ro, Nam-gu, Incheon 402-752, Republic of Korea
3. Radio Technology Group, Electronics and Telecommunications Research Institute, 218 Gajeong-ro, Yuseong-gu, Daejeon 305-700, Republic of Korea