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在低地球轨道通信系统中,由于系统的高动态,使扩频应答机接收的信号附加了几十千赫兹的多普勒频移,传统的伪码捕获方法很难完成捕获.对此提出了一种部分相关和FFT(Fast Fourier Transform)相结合的捕获方法,利用FFT补偿多普勒造成的相关峰损失,在搜索码相位的同时得到多普勒频移的估计,减少了捕获时间.给出了捕获系统的结构,分析了FFT对相关峰的补偿性能,给出了部分相关和FFT的参数设计方法,使用了自适应门限技术,以满足输入信号载噪比大幅变化的情况下实现伪码的捕获判决.理论分析和仿真结果表明:该方法可以在高多普勒频移和低载噪比环境下实现伪码的快速捕获,比其他快捕方法占用更少的FPGA(Field Programmable Gate Arrays)资源.
In low-Earth orbit communications systems, traditional pseudo-code acquisition methods make it difficult to achieve acquisition due to the high dynamics of the system, which adds a Doppler shift of tens of kilohertz to the signal received by the spread spectrum transponder A combination of partial correlation and FFT (Fast Fourier Transform) capture method, the use of FFT to compensate for Doppler correlation caused by the peak loss, the search code phase at the same time Doppler frequency shift estimation, reducing the capture time. The structure of the acquisition system is analyzed, the compensation performance of the FFT for the correlation peak is analyzed, the partial correlation and the parameter design method of the FFT are given, and the adaptive threshold technique is used to meet the requirement that the input signal to noise ratio is greatly changed Code capture decision.The theoretical analysis and simulation results show that this method can capture pseudo-code quickly under high Doppler shift and low carrier-to-noise ratio, occupy less FPGA (Field Programmable Gate) Arrays) resources.