1. School of Electronics and Information Engineering; Southwest University; Chongqing 400715 China
2. College of Computer Science; Chongqing University; Chongqing 400044 China
3. Department of Electronic Engineering; City University of Hong Kong; Kowloon Hong Kong
4. Department of Computer and Information Science, Faculty of Science and Technology; University of Macau; Taipa Macau
5. Department of Information Engineering; Chongqing Communication Institute; Chongqing 400035 China
6. School of Economics and Business Administration; Chongqing University; Chongqing 400044 China