A New Structure for NC-MC-CDMA in Cognitive Radio Networks

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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.