1. School of Software Technology Dalian University of Technology and Key Laboratory for Ubiquitous Network and Service Software of Liaoning Province, Dalian 116023, and Shaanxi Key Laboratory of Network and System Security, Xidian University, Xian 710071, China
2. School of Software Technology Dalian University of Technology and Key Laboratory for Ubiquitous Network and Service Software of Liaoning Province, Dalian 116023, China
3. Department of Computer Science University of North Carolina Greensboro NC, USA
4. School of Software Technology Dalian University of Technology and Key Laboratory for Ubiquitous Network and Service Software of Liaoning Province, Dalian 116023, and Acoustics Science and Technology Laboratory, Harbin Engineering University, China