Capacity evaluation in OFDMA cognitive radio networks

In this paper, we evaluate the total ergodic capacity of channels in an OFDMA cognitive radio network using the interference concept. It is assumed that all links associated with primary and secondary networks experience Rayleigh fading. The optimum power allocation scheme and the channel capacity are derived under different secondary to primary interference constraints. These constraints at the primary receiver belong to the following two types: the first one is the long-term constraint that regulates the average interference across all the fading states, and the other is the short-term constraint that limits the instantaneous interference over each fading state. Simulation results show the impact of the interference from other primary transmitters on the ergodic capacity of cognitive radio networks over the same subchannel.