[1] Lucent Technol Co Ltd, Bell Labs China, Shanghai 200030, Peoples R China
[2] Hong Kong Univ Sci & Technol, Dept Comp Sci, Hong Kong, Peoples R China
[3] Hong Kong Univ Sci & Technol, Dept Elect & Elect Engn, Hong Kong, Peoples R China
[4] Shanghai Jiao Tong Univ, Dept Comp Sci, Shanghai 200030, Peoples R China