Joint spectral shaping and power loading for OFDM-based cognitive radio

In this paper, we propose joint spectral shaping and power allocation for an orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR). The objective is to maximize its downlink transmission rate subject to the constraint on the interference introduced to the primary user (PU) spectrum band that coexists side-by-side in overlay approach. Considering that the CR transmitter (base station) is operating in an interference limited rather than the power limited scenario, we develop an optimal power allocation scheme that is augmented with active interference cancellation (AIC)-based spectral shaping and investigate its performance. We also propose an AIC-based suboptimal scheme which is computationally less complex and offers performance very close to the AIC-based optimal scheme. For a given interference threshold prescribed by the PU system, experimental results show that the proposed AIC-based optimal as well as the suboptimal schemes can offer much higher transmission rates for the CR user compared to the conventional schemes available in the literature for the same problem under similar scenario.