卫星扩频应答机的伪码快捕方法

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.

Fast PN code acquisition for satellite spread spectrum transponder

Large Doppler offsets are inherent to direct spread spectrum signal due to high dynamic environment in low earth orbit satellite communication scenarios. Frequency offset can be dozens of kilohertz, which cause traditional acquisition approach failed to complete PN code acquisition. A part-coherent combined with FFT technique was proposed for this problem. It utilized fast Fourier transform(FFT) to compensate coherent loss resulted by frequency shifts. It simultaneously searched code phases and got Doppler offsets, thus acquisition time could be significantly reduced. Acquisition structure was given, and FFT compensate performance was analyzed. The selection of part-coherent parameters and FFT points were given. Auto adaptive threshold technical was used to realize code acquisition when input signal power varied widely. Theoretical analysis and simulation results verify that the approach can complete fast code acquisition in high Doppler shift and low signal to noise ratio environment, and take up fewer field programmable gate arrays resources.