Opportunistic Cooperation for Distributed Spectrum Sensing in Cognitive Radio

We consider a set of cognitive nodes cooperatively sensing the activities of a primary system. Two cooperative protocols are proposed, where cognitive nodes opportunistically transmit to each others, and finally each node makes a decision based its own observations. In the first protocol (Protocol~1), a node relays the signal received from the primary to the other nodes only if the signal energy is sufficiently large. In the second protocol (Protocol~2), given the knowledge of channel gains to the other nodes, a node transmits only if the channel gains are large. With two cognitive nodes, Protocol~1 improves the average detection probability by up to 50\% relative to the protocol studied in~\cite{Li2007a}. Compared to Protocol~1, while additional channel knowledge is needed, Protocol~2 saves up to 50\% transmit power and maintains almost the same detection probability.