A mathematical model for computing the out-of-band(OOB) leakage radiation in NC-OFDM systems and the interference to the adjacent primary users(PUs) is presented in this paper.Based on this mathematical model,the optimal parameters could be obtained by solving the nonlinear programming(NLP) problem subject to secondary users(SUs)' spectrum overhead and PUs' occupancy rate r.The results showed the close relationship between the number of guard subcarriers and the parameters of input back off(IBO) as well as ...