1. Software Engineering Institute; East China Normal University; Shanghai 200062 China
2. Wuxi SensingNet Industrialization Research Institute; Wuxi 214213 China
3. Research Center of Ubiquitous Sensor Networks; University of Chinese Academy of Sciences; Beijing 100049 China
4. Electrical and Computer Engineering, Faculty of Engineering and Applied Science; Memorial University of Newfoundland; St. John's NL A1B3X5 Canada