Cognitive Coded Cooperation in Underlay Spectrum-Sharing Networks Under Interference Power Constraints

Since the radio-frequency spectrum is fast becoming scarce, increasing the spectral utilization is of utmost importance for the sustainable development of wireless communications systems. In an effort to improve the spectral efficiency, cooperative relaying techniques have recently been integrated into spectrum-sharing environments. In this paper, we examine the outage and bit error probabilities of dual-hop cognitive turbo-coded cooperative networks with outdated channel state information (CSI) subject to Rayleigh fading. We assume a spectrum-sharing environment where the transmit power conditions of the underlay network are governed by the combined power constraint of the interference in the primary network and the maximum allowable transmission power at the secondary network. In this network, cochannel interference from the primary transmitter on the secondary network is considered, and a single relay that maximizes the received signal-to-noise ratio (SNR) is selected among the secondary relays. To efficiently evaluate the key parameters on the system performance, we derive the analytical expressions of the end-to-end outage probability and bit error rate (BER) for the proposed scheme. Assuming binary phase-shift keying (BPSK), we obtain explicit upper bounds on the probability of bit error based on the pairwise error probability. Furthermore, we present simplified expressions of the outage probability in the high-SNR regime used to quantify the system performance in terms of diversity gain. Finally, simulation results are provided to verify the accuracy of our analytical framework.