Date Added: Nov 2009
Cooperative relaying helps improve the reliability of data transmission over wireless fading channels. In orthogonal relay protocols the source and the relay terminals transmit over orthogonal channels, allowing a simple receiver at the destination. These protocols achieve the maximum diversity gain but suffer from reduced multiplexing gain. In cooperative relay communications, users help each other by acting as a relay for other users' signals. Cooperative relaying creates virtual antenna arrays and realizes spatial diversity (even) with single antenna terminals. In recent times, there has been enormous interest in devising efficient cooperative relay protocols for half-duplex terminals. The cooperative protocols can broadly be classified as either orthogonal or non-orthogonal.