To achieve the goal of high data rate and QoS, the future 5G will adopt the Cognitive Radio System, which can support unlicensed users to utilize licensed users' spectrums when they are unoccupied. Since the spectrums used by unlicensed users are not continuous, it is necessary to use NC-OFDM which can invalidate subcarriers to avoid interference with the licensed users. In this case, lots of random zero in-puts/outputs, which are unnecessary to calculate, will appear in the IFFT/FFT modules of NC-OFDM. Therefore, it is necessary to reduce computation complexity and improve data rates in 5G by ignoring those zero inputs/outputs. In this paper, we have advanced an innovative pruning algorithm based on Radix-2/4 and SRFFT, which can ignore random zero inputs/outputs with the help of pruning matrix intelligently. Through simulating and comparing the computation complexity with other FFT algorithms, we found that the proposed algorithm is more achievable in hardware and has less twiddle factors to calculate than others when a few random inputs/outputs are available.
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