1. School of Electrical and Electronic Engineering, Shandong University of Technology, Zibo 255000, P. R. China
2. College of Electronics and Information Engineering, Shenzhen University, Shenzhen 518060, P. R. China
3. School of Electronic Engineering and Computer Science, Queen Mary University of London, London E1 4NS, UK
4. Department of Embedded Systems Engineering, Incheon National University, Incheon 22012, South Korea