A new structure for NC-MC-CDMA in cognitive radio networks

Multicarrier-based waveforms offer significant advantages for opportunistic cognitive radio systems through the ability to shape the spectrum of transmitted signal by deactiving subcarriers. In MC-CDMA based cognitive radio, deactiving some subcarriers to avoid interference with primary users, causes the loss of orthogonality among the spreading codes and therefore the performance of the system reduces. On the other hand, different structures which are proposed for equalizer in traditional MC-CDMA receiver cause many problems. For example MRC and EGC cause the loss of orthogonality among the users´ signals; ZF introduces noise amplification and MMSE increases receiver´s complexity. In this paper a new structure for NC-MC-CDMA system is introduced which solves the spreading codes´ problem. Furthermore, it will be shown that this structure reduces receiver complexity by removing equalizer. The performance of the new structure is investigated theoretically and simulation results evaluate the performance of the system. As it will be shown, by removing the ISI with this new structure, system´s performance in fading channel is similar to AWGN channel that is prominent progress in respect of traditional MC-CDMA system.