1. College of Computer Science, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
2. School of Computer and Information, Anqing Normal University, Anqing 246011, China
3. High Technology Research Key Laboratory of Wireless Sensor Network of Jiangsu Province, Nanjing 210023, China
4. Department of Computer Science and Media Technology, Malmö University, Malmö 20506, Sweden