During my studied I have received financial support from Jenny ja Antti Wihurin Rahasto, Elektroniikkainsinöörien Seura, Emil Aaltosen Säätiö, Nokia Foundation, Fulbright, and Tekniikan Edistämissäätiö. This support is gratefully acknowledged. I am thankful to my parents Pirjo and Risto Luukkonen, and to my sisters Hanna, Eeva, and Liisa for the encouragement during the whole course of my studies.Finally, my dearest thanks are to Satu for your support throughout my studies and research.