A GPS signal acquisition algorithm for the high orbit space

In the high orbit space, the visibility of GPS main lobe signal is poor due to the earth's occlusion and the increase in signal transmission distance. Therefore, the side lobe signals are essential for navigation mission, which puts forward higher requirements for the sensitivity of the receiver. In addition, the cross-correlation interference (CCI) caused by the large power difference between the main and side lobe signals is serious and results in the false acquisition of the side lobe signals. To improve the acquisition sensitivity and stability of the receiver, we designed a GPS signal acquisition algorithm for the high orbit space. The characteristics of high orbit GPS signal are analyzed according to the propagation process of GPS signal link. The influence of CCI on the acquisition performance of the side lobe signals is explored. Based on the parallel code phase search method, the coherent accumulation and incoherent accumulation are combined to improve the acquisition sensitivity. At the same time, according to the different probability distribution characteristics of autocorrelation peak and cross-correlation peaks in the correlator output, CCI is detected by means of hypothesis testing. The strong signals are reconstructed by using the amplitudes, code phases and Doppler shifts provided by the tracking loop. The CCIs are estimated by correlating the reconstructed strong signals with the local duplicated signals and eliminated from the correlation results of the side lobe signals to obtain the correct acquisition results. Simulation results show that the proposed algorithm can eliminate the CCIs in the high orbit space and improve the acquisition sensitivity of the receiver. Moreover, the CCIs under different Doppler shift differences of the main and side lobe signals can be effectively eliminated.