I would like to express my sincere thanks to my thesis advisor, Dr. Wipawee Hattagam for her invaluable help and constant encouragement throughout the course of this research. I am most grateful for her teaching and advice, not only the research methodologies but also many other methodologies in life. I would not have achieved this far and this thesis would not have been completed without all the support that I have always received from her. In addition, I am grateful for the teachers of telecommunication engineering: Asst. Prof. Dr. Rangsan Wongsan, Dr. Rangsan Tongta, and others person for suggestions and all their help. Finally, I most gratefully acknowledge my parents and my friends for all their support throughout the period of this research.