There were many people who helped me during my Ph.D, and I would like to take this opportunity to thank them. First and foremost, I would like to express my appreciation and gratitude to my supervisors, Professor XIE Lihua and Professor ZHANG Cishen (currently at Swinburne University of Technology, Australia), for years of invaluable guidance, encouragement, and financial support. Professor Zhang was the first person who introduced me to the scientific world. Thanks to Professor Xie for his endless patience, thoughtful discussions, and the many opportunities and the freedom he has offered that allowed me to find the research topics I was most interested in. This thesis would not have been possible without their enthusiastic help. Thanks also to Dr. LU Wenmiao, Dr. Arian Maleki and Professor Richard G. Baraniuk for their collaborations and fruitful discussions. I would also like to thank several fellow graduate students, postdocs and visiting scholars for their help and support in both research and life. In particular, thanks to