1. College of Computer, Nanjing University of Posts and Telecommunications, Mail Box 157, No. 66, Xinmofan Road, Nanjing 210003, China
2. Jiangsu High Technology Research Key Laboratory for Wireless Sensor Networks, Nanjing 210003, China
3. Key Lab of Broadband Wireless Communication and Sensor Network Technology of Ministry of Education, Nanjing 210003, China
4. College of Computer Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China