where S is the modulated M-ary QAM symbol.
On the receiver side, the received signal, r =[ r0,r1,...,rN−1], is correlated with the local reference FMW to recover input data symbols by demodulate maximum correlation output. It should be note that, the local reference FMW on the receiveris highly dependent on spectrum available vector.
Since the information on S is hidden in the background noise by spreading over all available spectrum bins, cognitive-CDMA signals have a low probability of being intercepted by unauthorized listeners