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在低轨道卫星(LEO)通信链路中,由于星地之间相对运动速度较快而存在较大的多普勒频移,为了保证通信质量,必须对多普勒频移进行补偿。基于DDS+PLL技术实现对多普勒频移补偿的方法是一种开环控制方式,这种方法结合了DDS的频率分辨率高和频率捷变速率快等优点,以及PLL具有的窄带滤波跟踪特性。分析了DDS频率阶跃对于PLL输出响应的瞬态影响,并且给出了相应的改善方法。该技术已经在工程中得到应用和验证。
In LEO communication links, Doppler shift has to be compensated due to the large Doppler shift due to the relative velocity between the earth and the satellite. To ensure the communication quality, Doppler shift must be compensated. The method of Doppler shift compensation based on DDS + PLL technology is an open-loop control method. This method combines the advantages of high DDS frequency resolution and fast frequency agility, as well as narrowband filter tracking characteristic. The transient effects of the DDS frequency step on the PLL output response are analyzed, and the corresponding improvement methods are given. This technology has been applied and verified in engineering.