Cognitive radio-based OFDM sidelobe suppression employing modulated filter banks and cancellation carriers

In this paper, we propose a novel sidelobe suppression approach for cognitive radio systems employing orthogonal frequency division multiplexing (OFDM) transmission. OFDM is a promising solution for future overlay wireless access due to its high data rate and flexibility. However, OFDM and its variants employ sinc-type pulses in representing the symbols transmitted over all subcarriers during one time instant. Consequently, large sidelobes can occur that could potentially interfere with the signal transmissions of the neighboring legacy systems or with the transmissions of other rental users. To mitigate this source of interference, both cancellation carriers (CCs) and modulated filter banks (MFB) can be employed. In this paper, raised-cosine filter is chosen without loss of generality as the prototype filter for the modulated filter banks. The power spectrum density of the OFDM signal after employing different CC algorithms, different number of CCs and different parameters of raised-cosine filters, such as the roll off factor, are analyzed and compared. Simulation results show that this combination approach can achieve significant reduction for OFDM out-of-band radiation and the sidelobe can be suppressed down to -70 dBm.