1. School of Mathematics, Southeast University, Nanjing, China
2. School of Mathematics, Frontiers Science Center for Mobile Information Communication and Security, Southeast University, Nanjing, China
3. School of Electrical Engineering, Korea University, Seoul, South Korea
4. School of Media and Information Engineering, Yunnan Open University, Kunming, China
5. School of Mathematical Sciences, Key Laboratory of Intelligent Education Technology and Application of Zhejiang Province, Zhejiang Normal University, Jinhua, China
6. Department of Engineering, King's College London, London, U.K.