Outage performance improvement with cooperative relaying in cognitive radio networks

In this paper, we investigate the outage probability in three different relay modes, namely Amplify-and-Forward (AF), Decode-and-Forward (DF), and Hybrid Decode-Amplify-Forward (HDAF). We derive the closed-form outage probability expressions for cooperative communication. Our aim is to ensure the quality of service (QoS) of the primary link while minimizing the outage probability of the cognitive radio user. The cooperation based spectrum access is investigated at the secondary network. The cognitive transmitter will allocate low power if the quality of service is very rigid. Firstly, it is beneficial that the cooperation is obtained at the cognitive user from the surrounding cognitive users to decrease outage probability. Secondly, we select the best relay that can provide the minimal outage probability for cooperation. Finally, we investigate the outage probability under the peak and average interference constraints. The results indicate that the average interference constraints has lower outage probability than the peak interference constraints, due to the power adaptation between the transmitter and relay. The comparison among three cooperation relay modes shows that the HDAF outperforms the AF and DF. At the same time, we can see that the performance gain of the HDAF cooperation is better than the other modes, and a lower outage probability can be acquired as the number of potential relays increases.