Demonstration of hybrid overlay/underlay waveform generator with spectrally compliant cognitive capability via SD-SMSE framework

In this paper, a software defined radio (SDR) based waveform generator platform with spectrally compliant cognitive capability for cognitive radio (CR) and dynamic spectrum access (DSA) network is demonstrated. In our previous work, an overlay CR has been demonstrated via a spectrally modulated spectrally encoded (SMSE) framework to autonomously stitch unused spectrum fragments and transmit over non-contiguous frequency bands in a dynamically changing environment. Such an overlay CR can coexist with primary users (PUs) and other secondary users (SUs) without harmful interference by turning off the subcarriers which are shared with active PUs and other SUs on the band. To further enhance spectrum usage, we extend it and implement a hybrid overlay/underlay waveform generator via a soft-decision SMSE (SD-SMSE) framework, where both unused and under-used spectra are explored. Specifically, the hybrid overlay/underlay waveform can transmit over not only unused spectrum bands, but also under-used spectrum and share the spectrum with active PUs and other SUs by underlaying them, since PU/SU has certain capability to tolerant interference as long as the underlay transmission power is lower than such a interference tolerance level (ITL). On the other hand, if any active SU on the band is not a friendly transmission, the hybrid waveform can easily increase the transmission power underlaying with the SU much higher than the ITL to fully disrupt the unfriendly transmission. Moreover, the proposed platform is capable of generating conventional single-carrier waveform with different modulation schemes and radio frequency (RF) parameters. Therefore, the platform implements many desirable functions, realizes coexistence with PUs and other SUs or unfriendly transmission disruption, and maximizes the spectrum efficiency, as well as provides a testbed for cognitive radio and cognitive RF research and development.