[1] Beijing Inst Technol, Sch Informat & Elect, Beijing 100081, Peoples R China
[2] Nanjing Univ Informat Sci & Technol, Sch Comp & Software, Nanjing 210044, Jiangsu, Peoples R China
[3] Univ Oslo, Dept Informat, N-0316 Oslo, Norway
[4] Simula Metropolitan Ctr Digital Engn, Fornebu, Norway