GNSS数字下变频设计与分析

Design and Analysis of Digital Down Conversion for GNSS

针对数字下变频滤波会造成信号相位延迟的特性以及GNSS接收信号存在多普勒频移问题,设计了应用于GNSS信号的数字下变频补偿方法。通过分析输入数字中频信号与滤波器频域特性,得到输入中频信号与滤波后信号之间的相位差。滤波后的信号通过FFT乘以这个相位因子,再进行IFFT恢复原始相位,补偿了传统数字下变频带来的相位延迟和多普勒频移丢失,通过对比分析原始接收数据与数字下变频补偿后的数据的捕获结果证明,软件接收机能够正确捕获GNSS信号码相位和多普勒频移。

Considering that the Digital Down Conversion （DDC） filtering may cause phase delay of signal, and the received Global Navigation Satellite System （GNSS） signal has Doppler frequency shift, we present here a DDC compensation technique applied to GNSS signal. Through analyzing the fi＇equency-domain characteristic of input IF digital signal of the filter, the phase difference between the input signal and the filtered signal is obtained. The filtered signal multiplies the phase factor after FFT and then restores the original signal phase through IFFF, which can compensate the phase delay and Doppler frequency loss caused by DDC. Comparison is made to the originally received data and the one after DDC compensation, and the result shows that the code phase delay can be correctly compensated and Doppler frequency can be correctly acquired by the GNSS software receiver.