1. School of Electrical Engineering, University of Jinan, Jinan, P. R. China
2. Department of Computer Science, Brunel University London, Uxbridge, Middlesex, U.K.
3. College of Electrical Engineering and Automation, Shandong University of Science and Technology, Qingdao, P. R. China
4. Department of Mathematics, Brunel University London, Uxbridge, Middlesex, U.K.