1. State Key Laboratory of Precision Measurement Technology and Instruments; Tianjin University; Tianjin 300072 China
2. Tianjin Key Laboratory of Biomedical Detecting Techniques & Instruments; Tianjin University; Tianjin 300072 China
3. School of Electronics and Information Engineering; Tianjin Polytechnic University; Tianjin 300387 China
4. Viterbi School of Engineering; University of Southern California; Los Angeles 90007