Pursuing a PhD degree is definitely the most important decision I have made in my past life. The four-year study teaches me how to be a professional researcher to tackle the problems, a grown-up to work with other people and a mature guy to get along with myself. I have learnt from many brilliant people, who taught, helped and inspired me.It is time to express my sincere gratitude to them.First of all, I want to thank my supervisor Bo An. Without your supervision, this point can not be reached. Thank you for giving me the opportunity to pursue my PhD degree under your supervision. Four years ago, I joined your group without much knowledge about research. Thanks for your endless patience, insightful guidance and constant encouragement during every step of doing research. I am also deep impressed and motivated by your enthusiasm and profession to the research and those will be the fundamental things I will strive for in my future career. You reshapes my understanding about the research with your commitment to work on problems with impacts to the real-world and benefits to the society. Your critical comments always deepen my understanding on the research problems and the discussions with you always benefit me a lot.Not only on about research, I also learn a lot about the principles for the life: the way to dealing with failures because "rejection is a part of your academic life", the willingness to chase perfection and excellence because we always fight until the last minute of the conference deadlines and the love to Sichuan cuisine. Let me quote that "you set the pace and I will try to adjust to you". I will be forever grateful to your supervision and I hope I can let you be proud of me someday in the future.I would like to thank my Thesis Advisory Committee (TAC) members: Gao Cong, Rongxing Lu, Yilin Mo and Xiaohui Bei. Those discussions help me to improve the vii viii works and build a better vision of my research. Your guidance are valuable for me and I will always be thankful for your efforts in advising me.