Spectrally encoded code-division multiple access for cognitive radio networks

Recent studies have revealed that spectrum congestion is due to the inefficient usage of spectrum against the availability. Cognitive radio is viewed as an approach for improving the utilisation of radio spectrum. The spectrally encoded (spread-time) code-division multiple access (SE-CDMA) technique (which is regarded as the dual of spread spectrum CDMA) is considered and its performance in cognitive radio networks is studied. In cognitive network spectrum, overlay and underlay techniques are employed to enable the primary and secondary users to coexist while improving the overall spectrum efficiency. It is shown that SE-CDMA provides considerable flexibility to design overlay and underlay waveforms that are scenario-dependent. The performance of SE-CDMA method is evaluated in additive white Gaussian noise and fading channels in terms of both primary and secondary users. Moreover, its performance is compared with cognitive radio using soft-decision spectrally modulated spectrally encoded waveforms. The results indicate the efficiency of SE-CDMA.