1. Department of Information Science and Engineering, Yanshan University, Hebei Street, Qinhuangdao, Hebei Province, P. R. China
2. School of Electrical Engineering and Computing, The University of Newcastle, University Drive, Callaghan, NSW 2308, Australia
3. Department of Information Science and Engineering, Taishan University, Dongyue Street, Tai’an, Shandong Province, P. R. China