[1] Beijing Inst Technol, Sch Opt Engn, Beijing 100081, Peoples R China
[2] Beijing Jiaotong Univ, Beijing 100044, Peoples R China
[3] Sun Yat Sen Univ, Guangzhou 510006, Guangdong, Peoples R China
[4] Natl Univ Singapore, Dept Elect & Comp Engn, Singapore 119077, Singapore