Capacity of cognitive AF relay networks with multiple primary receivers

This paper evaluates the ergodic capacity of secondary dual-hop cognitive amplify-and-forward (AF) relay networks (CRNs) subject to arbitrary Nakagami-m fading. Considering a spectrum-sharing environment, we assume that the transmit power of secondary users is solely governed by the interference power constraint at N primary users. A closed-form expression for the ergodic capacity of the secondary AF CRN is derived for the first time and shown to be affected by the distance ratio of the interference link (from the secondary transmitter to the closest primary receiver) to the relaying link (between the secondary transmitter and the secondary receiver). This new ergodic capacity expression is validated and assessed by insightful simulations against different key CRN parameters.