1. School of Cyber Engineering, State Key Laboratory of Integrated Service Networks, Xidian University, Xi’an, China
2. Guangzhou institute of technology, State Key Laboratory of Integrated Service Networks, Xidian University, Guangzhou, China
3. Department of Electronical and Computer Engineering, University of Nebraska-Lincoln, NE, USA
4. Key Lab. of the Minist. of Educ. for Wide Band Gap Semiconductor Materials and Devices, Xidian University, Xi’an, China