1. Southwest Jiaotong University,School of Information Science and Technology,Chengdu,China
2. Southwest Jiaotong University,School of Mathematics,Chengdu,China
3. University of Essex,School of Computer Science and Electronics Engineering,Colchester,U.K.,CO43SQ
4. University of Electronic Science and Technology of China,National Key Laboratory on Communications,Chengdu,China
5. Southwest Jiaotong University,Key Lab of Information Coding and Wireless Comms,Chengdu,China