1. School of Electronic and Information Engineering, Beijing Jiaotong University,Beijing,China,100044
2. Institut fur Nachrichtentechnik, Technische Universitat Braunschweig,Braunschweig,Germany,38106
3. ZTE Corporation,State Key Laboratory of Mobile Network and Mobile Multimedia Technology,Shenzhen,Guangdong,China,518055
4. China Research Institute of Radiowave Propagation,Qingdao,China,266107