A novel hybrid overlay/underlay Cognitive Radio waveform in frequency selective fading channels

Cognitive radio (CR) has attracted strong interest recently to solve the spectrum congestion problem. In conventional cognitive radio, either overlay waveform is used to exploit unused (white) spectrum holes to avoid interference to primary users, or underlay waveform is employed to spread over a ultrawide bandwidth with extremely low power spectrum density to minimize interference to primary users. In our previous work, we proposed a novel hybrid overlay/underlay waveform to combine the benefits of both overlay and underlay waveform, creating a soft decision cognitive radio to exploit both the unused (white) spectral regions and the underused (gray) spectral areas. Extending the spectrally modulated spectrally encoded (SMSE) framework, we provide the framework for the proposed soft decision cognitive radio. We also evaluate the performance of the hybrid overlay/underlay waveform in frequency selective fading channels. A simulated performance analysis of overlay, underlay and hybrid overlay/underlay waveforms in frequency selective fading channels is presented and benefits discussed.