Manuscript received March 28, 2019; revised July 1, 2019; accepted July 10, 2019. Date of publication August 12, 2019; date of current version January 4, 2020. This work was supported in part by the National Key Research and Development Program of China under Grant 2017YFB1401300 and Grant 2017YFB1401303, in part by the National Natural Science Foundation of China under Grant 61875068, Grant 61873220, Grant 61673329, and Grant 61505064, in part by the Research Grants Council of Hong Kong under Project CityU 11205015 and Project CityU 11255716, and in part by the Fundamental Research Funds for the Central Universities under Grant CCNU18ZDPY10 and Grant 2017YBZZ009. Paper no. TII-19-1099. (Tingting Liu and Hai Liu contributed equally to this article.) (Corresponding author: Hai Liu.) T. Liu is with the National Engineering Research Center for E-Learning, Central China Normal University, Wuhan 430079, China, and also with the School of Computer Science, Carnegie Mellon University, Pittsburgh, PA 15213 USA (e-mail:,tingtin3@andrew.cmu.edu).
