Asymptotic capacity analysis in point-to-multipoint cognitive radio networks

In this paper, we analyze the asymptotic capacity in a spectrum sharing system where a secondary access point (SAP) restrictively utilizes the licensed spectrum of an active primary user (PU) to broadcast information to multiple secondary users (SUs) simultaneously, as long as the interference power inflicted on the PU is less than a predefined threshold. At the SAP, interference channel state information (CSI) between the SAP and the PU is used to calculate the maximum allowable SAP transmit power to limit the interference. We first derive the average capacity when perfect CSIs are known at the SAP based on extreme value theory. When the CSIs are imperfect, specifically, the interference CSI is imperfect, or the CSI of the SU transmission channel is imperfect, which is an important scenario for the secondary system. Then we characterize the capacity loss where perfect CSIs are not always available at the SAP.