1. School of Computer Science and Technology, Harbin Institute of Technology, No. 92 West Dazhi Street, Harbin 150001, China
2. Department of Electrical Engineering, National Cheng Kung University, Road 1, Tainan 70101, Taiwan
3. Institute of Computing Technology, Chinese Academy of Sciences, No. 6 Kexueyuan South Road, Zhongguancun, Beijing 100190, China
4. Electronics and Telecommunications Research Institute, 138 Gajeongno, Yuseong-gu, Daejeon 305-700, Republic of Korea