Throughout my postgraduate study, I feel that PhD life can be condensed to be a process of simply iterating from finding a question and then discovering a systematical solution after having a bee in one's head. However, during the process, various professional skills have been developed, including quickly reading/writing a technical paper, systematically thinking a problem, presentation skills and social communication and so on. In the last four years, I could haven't finished my PhD studies without many people's help. I have been very fortunate to work with all the great people. I would like to express my gratitude to the following organizations and people for their support and contribution: Ministry of Education, Singapore and Nanyang Technological University, Singapore, for offering me MOE undergraduate scholarship and the NTU research scholarship respectively to pursue a higher degree. Associate Professor Ng Wee Keong, my Ph.D. supervisor, for his invaluable guidance, advice, encouragement, and sharing of his knowledge. Only from him, I started to know the world of research and to do the research seriously as a part of my life. Also from him, I have learned how to tackle a problem systematically, deeply, and carefully. Through individual discussions, he inspired me of many good and invaluable questions to my research and of my passion to discover more solutions. I have also learned how to write a paper and present my work properly and clearly from him after his patient face-to-face tutoring. Without his supervision and encouragement, I would never have achieved the outputs in the thesis. I am very thankful to Dr. Vincent C. S. Lee and Dr. Philip S. Yu for their kindness and invaluable discussion during the period they visited NTU. With those i ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library discussions, new interesting and problems have been inspired. Their comments and suggestions on my draft papers are very helpful to make them professional. Additional thanks go to Dr. Sun Aixin, Dr. Vivekanand Gopalkrishnan, and Dr. James Cheng for their helps and encouragement whenever I have problems. I would also thank Dr. Li Xiang for her kind supervision and guide on my Final Year Project during my undergraduate study.