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 demodulating maximum correlation output. It should be note that, the local referenceFMWonthereceiverishighlydependentonspectrum 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