Cognitive underlay communications with imperfect CSI: Network design and performance analysis

This paper is concerned with performance analysis of cognitive underlay partial relay networks with imperfect channel state information (CSI). To assure the required quality of service (QoS) at primary receivers, transmit power at secondary nodes is adjusted by using a back-off power scheme under imperfect CSI condition. The back-off power strategy reduces transmit power at secondary nodes and in turn degrades the secondary network performance. Under the performance tradeoff between primary and secondary networks, this paper considers the use of multiple antennas at destination node and partial relay selection to enhance the secondary network performance without sacrificing the performance of the primary network. To justify the benefit of using the network design, several analytical and simulated results of the network performance are provided under various system settings.