School of Electronic and Information Engineering;
Lanzhou Jiaotong University;
Lanzhou 730070;
China;
School of Information Science and Engineering;
Lanzhou University;
Lanzhou 730000;
China;
Institute of Computing Technology;
Chinese Academy of Sciences;
Beijing 100190;
China;
Department of Computing;
School of Informatics;
University of Bradford;
Bradford BD71DP;
UK;