GNSS signal acquisition method on the high earth orbits spacecraft
To resolve the contradiction between the sensitivity and the resource limitation of Global Navigation Satellite System (GNSS) signal acquisition on the high Earth orbit spacecraft, a novel method based on comb filtering with high-speed processing is proposed. A comb filter is used to increase correlation gain by integration of multiple code cycles. And the integral output is processed in fast clock to reduce computational cost of correlation. The FFT/IFFT transform is carried out to search code phases in parallel. The Doppler compensation is analyzed to reduce high-dynamic signal loss and its mathematical expression is also derived. A FPGA implementation routine is presented and hardware-in-loop tests are also taken. The tests show that the acquisition sensitivity is better than −173 dBW. Compared to the NASA Navigator receiver, with similar acquisition sensitivity, the correlational computation reduces by 42%, the acquisition time reduces 61% and the acquisition Doppler range per search enlarges 2.5 times approximately. The method can acquire Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) signals and it has been verified on the high Earth orbit spacecraft, i.e. the Shijian 17 satellite.