First and foremost, I would like to express my most sincere gratitude to my supervisor Prof. Yap Kim Hui, who not only accepted me as his Ph.D student, but also provides constant guidance during the time of my research in Nanyang Technological University. Prof. Yap is professional and knowledgeable, and he regularly challenges and stretches me to do better at each research work. This thesis is completed with his regular support and encouragement.My sincere appreciation also goes to Dr. Sharmili Roy for her advice, motivation, and encouragement. Her insightful views and precious suggestions not only broaden my horizons, but also helped me cross many hurdles during my research time. She is both a good mentor and a good friend that can share life experiences.Thank you to my thesis advisory committee (TAC) members Prof. Lin Wei Si and A/Prof. Chau Lap Pui for their great support and encouragement.