Cognitive OFDMA: Exploring a new FFT based detection technique for opportunistic usage

In this paper, a new opportunity search technique is introduced for OFDMA based Cognitive Radio systems. In [1],which forms a basis for this study, the conventional opportunity search method was utilized for various subcarrier allocations where power spectral density calculations were used. Since all possible spectral gaps could not be found using the conventional technique, in order to increase the detection rate, a new technique is presented in this paper, which involves more than just determining the power in a frequency band. In the proposed technique, the opportunity search is done at the receiver part with synchronization stage and utilizing FFT calculations after removing cyclic prefix. Also it has been shown that by using the proposed technique all opportunities can be found when AWGN channel is considered without any impairments such as frequency offset and delay. Performance of the proposed technique is presented in comparison with the the conventional PSD method, and effects of OFDM impairments are studied individually. Simulation results show the superiority of the new technique in terms of true detection rates.