Constellation Design for Cooperative Communication

In this paper, a single-hop single-relay system with a direct link between the source and the destination is considered when the relay operates in the half-duplex mode. Motivated by the concept of signal space diversity, this paper introduces signal space cooperation, in which cooperation between the source and the relay is achieved using a novel constellation design. In this approach, the original constellation is expanded so that each member of the new constellation inherits its components from members of the original signal set. The expanded constellation enables the relay to extract the required information in order to cooperate in the relay phase, and it helps the destination to effectively combine received signals during the broadcast phase and the relay phase. The analytical study of the proposed scheme leads to the development of two design criteria for the constellation expansion. Numerical results depict superior performance in comparison with other cooperative schemes such as the distributed turbo code schemes.