A Bandwidth-Efficient Cognitive Radio With Two-Path Amplify-and-Forward Relaying

This letter introduces a new cognitive radio system employing the two-path amplify-and-forward relaying scheme. In the proposed system, the primary user (PU) transmitter cooperates with the secondary user (SU) transmitter and receiver to relay PU data to the PU destination. The proposed algorithm makes use of the interrelay interference (IRI) between the two relay nodes to transmit SU data and minimize their IRI effect on the PU destination. Two optimization problems are formulated to find optimal power allocation between SU transmission and relaying amplifying factors: one to minimize the probability of error and the other one to maximize the average achievable rate. Simulation results show that the proposed algorithm outperforms the single data transmission and the existing two-path relaying scheme. In addition, the PU network achieves a diversity order of 3, when a maximum-likelihood decoder is used, whereas the SU network achieves a diversity order of 2.