Study On GNSS Signal Receiving Technique Under Challenge Condition

Satellite navigation is getting more and more popular.In many scenarios,the multipath signal and non-linear characteristics of the signal channel have become the main error sources of navigation systems.To improve the multipath mitigation performance and non-linear characteristics resistence performance under challenge condition,this paper studies the joint tracking technique of two signals with adjacent carrier frequencies and multiple sub-band signal processing technique.The main work and innovation are summarized as follows:1)To improve the multipath mitigation performance,the joint tracking technique for asymmetric dual-band signals is proposed,based on the signal characteristics of B1 C and B1 I.Firstly,the performance of asymmetric dual-band signals is analyzed comprehensively.The results show that the ranging accuracy and multipath mitigation performance are significantly improved.For instance,the ranging accuracy of B1dual-side band signal is improved by about 12 d B,and the area of its multipath error envelope is reduced by about 72%.Secondly,a tracking method based on the combination of upper and lower sideband discriminators is proposed.Based on the coherence of the upper and lower sidebands,a subcarrier tracking loop is constructed.By tracking this subcarrier,the tracking accuracy and multipath mitigation performance are improved.Finally,a method based on local code construction is proposed to improve the long-term multipath mitigation performance of B1 dual-band signals.2)For the case that one sideband of asymmetric dual-band signal is a pilot signal,a joint tracking method based on carrier phase difference is proposed.Firstly,the pilot signal is used to track its carrier,and the tracking sensitivity is improved by increasing integration period.Then,a subcarrier is constructed based on the phase coherence of two signals.Compared with the technique presented above,this technique can achieve better subcarrier tracking performance when the integration period of the pilot signal is longer than that of the data signal,and the multipath error envelope area is reduced by about 25.53%.3)The wide bandwidth and high sampling rate of high-order dual-band signals lead to high processing complexity and power consumption,the bandpass sampling technique is introduced,to reduce the sampling rate.The Doppler information of the sampled signal is retained completely so the tracking accuracy and multipath mitigation performance can be maintained.The method to select sampling parameters is analyzed,and the receiving performance under different sampling rates is simulated.The results show that the SNR loss caused by bandpass sampling is less than 0.5 d B,while the complexity can be reduced by 87% at most.4)The zero points of the autocorrelation function of high-order BOC signals leads to high computational complexity of the acquisition.The bandpass sampling technique can eliminate the zero points,as well as reduce the data rate.Thus,the computational complexity of acquisition is greatly reduced.an acquisition method based on subcarrier Doppler compensation is proposed,to reduce the acquisition performance degradation caused by subcarrier Doppler.Compared with the dual-band method,the proposed method can reduce 1/2 of the resources,and improve the detection performance by about 0.5 d B.5)The wideband signals are distorted seriously by the non-ideal characteristics of the channel,which leads to significant tracking error.To solve this problem,a multi-subband signal processing technique is proposed.The signal band is divided into several narrow subbands,and the channel of a single subband can be approximately ideal.Two joint receiving techniques based on subband measurements and subband loop information fusion are proposed.By tracking each subband,the influence of non-ideal characteristics is effectively reduced;by adjusting the tracking parameters,the accuracy can be better than that of broadband BPSK signals.