In recent years, relay systems have become a subject of intensive research interest as it has become evident that they can improve performances and extend the coverage area of wireless communication systems. Special attention has been dedicated to relay systems since the proposal appeared for their implementation in mobile cellular systems. Numerous studies conducted after that proposal have enabled the incorporation of OFDM based relay systems in the accepted standards for IMT-Advanced systems. Nowadays, these ongoing studies aim to define new solutions for performance improvement of the...