1. Xihua University, Chengdu, China
2. School of Computer Science and Electronics Engineering, University of Essex, Colchester, U.K
3. School of Information Engineering, Nanchang University, Nanchang, China
4. Department of Informatics, Selmer Center, University of Bergen, Bergen, Norway
5. Key Laboratory of Information Coding and Transmission, Southwest Jiaotong University, Chengdu, China