Department of Electrical Engineering Tsinghua University Beijing 100084 China;
Shanghai Institute of Microsyst & Information Technology CAS Shanghai 200050 China;
School of Information Science & Technology ShanghaiTech University Shanghai 200210 China;
University of Chinese Academy of Sciences Beijing 100039 China;
Guangzhou Power Supply Bureau Guangdong Power Grid Co. Ltd Guangzhou 510620 China;
Department of Computer Science University of Pittsburgh PA 15260 USA;
China Tower Company Limited Guangzhou518000 China;