Demodulation of Weighted Fractional Fourier Transform Encrypted Chaotic Direct Spread Signals over Multipath Fading Channels
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摘要: 为了在多径信道下解调加权分数傅里叶变换加密的混沌直扩(WFRFT-CD3S)信号，该文提出一种广义信道差分解调算法。在WFRFT-CD3S系统的发射端先对信息码进行差分调制，接收端将差分码与信道的乘积视为广义信道，并通过本地扩频序列构建频域匹配滤波器以估计广义信道冲击响应。接收端通过解差分广义信道冲击响应的估计值来合并各径能量并恢复信息码。对所提算法的误码率进行了理论分析，数值仿真验证了理论分析结果。数值仿真结果表明提出的解调算法可以在低信噪比下解调多径WFRFT-CD3S信号，保证了WFRFT-CD3S系统抗能量检测的能力。Abstract: To demodulate the Weighted FRactional Fourier Transform encrypted Chaotic Direct Sequence Spread Spectrum (WFRFT-CD3S) signal over multipath fading channels, a generalized channel differential demodulation algorithm is proposed. The transmitter of the WFRFT-CD3S system modulates differentially the message bits. The receiver regards the product of the differential code and the channel as a generalized channel, and constructs a frequency-domain matched filter through the local spreading sequence to estimate the generalized channel impulse response. The receiver combines the path energies and recovers the message bits by de-differentiating the estimates of the generalized channel impulse response. The bit error rate of the proposed algorithm is analyzed theoretically, and the theoretical results are verified by numerical simulation. The numerical simulation results show that the proposed demodulation algorithm can demodulate the multipath WFRFT-CD3S signal under low signal-to-noise ratio, which ensures the anti-energy detection capability of the WFRFT-CD3S system.
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