1. BNRist, Department of Automation, Tsinghua University, Beijing 100084, China, also with the Division of Systems Engineering, Boston University, Brookline, MA 02446 USA, and also with the Center for Information and Systems Engineering, Boston University, Brookline, MA 02446 USA.
2. Division of Systems Engineering, Boston University, Brookline, MA 02446 USA, and also with the Center for Information and Systems Engineering, Boston University, Brookline, MA 02446 USA.
3. BNRist, Department of Automation, Tsinghua University, Beijing 100084, China.
4. BNRist, Department of Automation, Tsinghua University, Beijing 100084, China, and also with the Tsinghua-Berkeley Shenzhen Institute (TBSI), Tsinghua University, Shenzhen 518055, China (e-mail: zhyi@tsinghua.edu.cn)