Abstract
Cognitive radio (CR) and dynamic spectrum access (DSA) are the effective ways to solve the spectrum congestion problem. Three kinds of basic DSA approaches are respectively dynamic exclusive use, open sharing and hierarchical access. The hierarchical access model is perhaps the most compatible with solving the current spectrum congestion problem. So, in this paper, we will set up an overlay DSA system which is an effective approach of the hierarchical access model. Firstly, we make use of the spectrally modulated spectrally encoded (SMSE) framework to generate OFDM waveforms for the secondary user (SU) which can be considered as the overlay waveform. Then we use the signal which is generated by the walkie-talkie to access the overlay DSA system as a primary user (PU) or an interference signal. The universal software radio peripheral (USRP) and spectrum analyzer are used to generate and analyze the power spectrum density (PSD) of the coexistence of a SU and a PU or an interference signal. The experimental result demonstrates that the overlay DSA system can achieve the function of turning off the sub-carriers corresponding to the frequency of the PU. It also shows that the system can greatly improve the efficiency of the spectrum utilization due to dynamically allocate the spectrum.
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