, for their continuous assistance. They have help made my Ph.D. journal enjoyable, interesting and fruitful. Special thanks to my colleague, Mr. Yu Hang for providing help and suggestions throughout the four years. It won't be easy to complete my research without all of you. I also thank the School of Electrical and Electronic Engineering of Nanyang Technological University for awarding me the postgraduate scholarship as the financial support in my PhD candidature period. Lastly, I owe a big debt of gratitude to my parents for their selfless love, inspiring support and continuous encouragement.