1. Graduate School of Science and Engineering, Ibaraki University, Ibaraki, Japan
2. Faculty of Science and Technology, Nanzan University, Nagoya, Japan
3. Radio Equipment Development Department, Radio Network Division, DOCOMO Technology, Inc, Kanagawa, Japan
4. School of Computer, National University of Defense Technology, Changsha, China
5. School of Computer Science, Univ. of Science and Technology of China, Hefei, China