A cooperative protocol for spectral-efficient cognitive relay networks

In this paper we propose a cooperative protocol for cognitive wireless networks that can improve the overall system spectral efficiency when a secondary user (SU) incorrectly transmits over the same resource with the primary user (PU). The interfering transmissions are received at relay nodes, that form the cooperative network, and are decoded with successive interference cancellation (SIC). Depending on the decoding results, each relay applies independently a space-time code (STC) to the result and then the relays forward the coded signals simultaneously. The advantages of the protocol are first that it operates passively without the need for source cooperation, and second that it does not adopt a different mode of cooperation for different average channel conditions. Comparative simulations with a state-of-the-art multi-source transmission protocol reveal that our protocol can minimize the impact of incorrectly detecting a PU transmission from the perspective of the overall system spectral efficiency.