Active interference cancellation based optimal power loading for OFDM cognitive radio

Active interference cancellation (AIC) is an effective spectral shaping technique for orthogonal frequency division multiplexing (OFDM)-based systems. In this paper, we propose an AIC-based optimal power loading scheme that aims to maximize the downlink transmission capacity of an OFDM-based cognitive radio (CR) system operating opportunistically within the licensed primary users (PUs) radio spectrum in an overlay approach. Since the CR transmitter may not have the perfect knowledge about the instantaneous channel quality between itself and the active PUs, the interference constraints imposed by each of the PUs are met in a statistical sense. For a given power budget at the CR transmitter and the prescribed statistical interference constraints by the PUs, the presented simulation results show that a relatively much higher transmission capacity can be achieved by the OFDM CR user when power allocation is augmented with AIC-based spectral shaping.