认知无线电(Cognitive Radio, CR)由于机会式利用空闲频谱，因此当授权用户突然出现或者和其他认知用户发生碰撞时，产生的干扰将会极大的降低认知无线电系统的性能。本文提出了基于分数傅里叶变换(Fractional Fourier Transform, FrFT)的认知无线电抗干扰系统，通过将在分数傅立叶变换域具有能量集中性的Chirp信号作为认知无线电的基带信号，能够在接收端通过特定阶数的分数傅立叶变换域的滤波处理提取有用信号的能量，抑制其他用户的干扰。仿真表明：当干扰为正余弦波时，本文系统要比未采用分数傅里叶变换的系统具有更低的误码率，而且本文系统能够有效地抑制多径干扰和其他多认知用户的干扰。

As the confliction between two cognitive radio （CR） systems and the interference among authorized users may degrade the performance of CR systems, an anti-jamming system for CR based on fractional Fourier transform （FrFT） is proposed. In this system, Chirp signal whose energy concentrates in FrFF domain is used as the base-band signal of CR, and the original data are restored via the filtering in FrFT domain and some correlative calculations. Simulated results show that the proposed system can extract the energy of expected signals and effectively suppress muhipath interference and the interference of other cognitive users, and that, when the interference is a cosine signal, bit error rate of the proposed system is lower than that of the system without FrFT.