1. School of Computer and Communication Engineering, Tianjin University of Technology, Tianjin 300384, China
2. School of Computer Science & Software Engineering, Tianjin Polytechnic University, Tianjin 300387, China
3. Department of Computer and Information Communication, Hongik University, Sejong Campus, Sejong 337-701, Republic of Korea
4. Department of Computer Science and Engineering, Konkuk University, Seoul 143-701, Republic of Korea