Effect of outdated CSI on buffer-aided underlay cognitive relay networks

This work studies the impact of outdated channel state information (CSI) on decode-and-forward (DF) buffer-aided underlay cognitive relay networks (CRNs), with the following three key constraints considered: the maximum transmit power of the secondary network (P), the peak interference power at the primary user (I) and the interference power at the secondary network caused by the primary network (P_PS). This makes it much more involved to handle with than existing works. By modeling the transitions of the buffer states with Markov chain theory, a closed-form expression of the outage probability for the system with finite-size buffers is derived, which depicts the impact of outdated CSI on the outage performance of buffer-aided CRNs. In addition, it is also demonstrated that the performance of the secondary network is improved with the increase of the interference threshold that the primary users can tolerate, but decreases with the increase of the transmit power of the primary network, which is useful in the design of buffer-aided CRNs. Monte-Carlo simulations are given to verify the validity of the theoretical analysis.