1. Department of Automation, University of Science and Technology of China, Hefei 230060, China.
2. Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milan, Italy, and also with the Institute of Advanced Technology, University of Science and Technology of China, Hefei 230060, China.
3. Department of Automation, University of Science and Technology of China, Hefei 230060, China (e-mail: zjli@ieee.org)