Research On Multipath Interference Suppression Of GNSS Receiver

Since GNSS advent,its has been widely applied in military and civilian areas. However,with the aim of precise strike of the modern war and the increasing need for the development of location based service industry, the standard on accurate positioning has been constantly pursued. In the past decades,most measurement errors in GNSS have been properly controlled, except for a special one-the multipath error, which has been a bottlenecked for a further advance of its accuracy. Because of the highly "environment-related" nature-the propagation path, signal amplitude and time delay, multipath error can neither be predicted nor eliminated through differential technology or any other routine methods. Therefore, the study of multipath has long been the hot issue of GNSS area.Firstly, the GPS system is taken for example in this article to study the composition of GNSS, the structure of navigation signals, as well as the principle and autocorrelation properties of the M-Sequence and the C/A code. The composition and the workflow of the GNSS receiver has been detailed analysized, so does the carrier tracking loop and the code tracking loop. Followed by the analyzing and summarizing of all types of errors in GNSS, and a conclusion was drew that it is of vital significance to decrease multipath error in order to achieve greater accuracy in navigation positioning.Since the nature of the GNSS signal is electromagnetic wave, the following analysis begins with the study of the propagation mode of the electromagnetic wave and disclose the fact that, multipath signal is dominated by the reflected signal which is directly related to the properties of the reflective surface. Then, the characteristics of the multipath signal is analyzed and its descriptive model is established. By referencing to the receiver's working principle and relative theories of multipath, some analyses and simulations are conducted to find out what effect of all multipath-signal parameters have on the carrier and the code tracking loop. At lase two commonly used time domain anti-multipath methods are introduced and contrasted.Thirdly, multipath estimation technology is an very effective method for multipath suppression, for traditional BPSK modulation signal, this paper created a multi-correlator estimate structure,and its noise characteristics was analyzed. Then the selection scheme of the sampling point and the estimation point on the maximum likehood estimation was optimized.For the "noise bottleneck" in this estimation,the analyzation indicate that this phenomenon is caused by the ill-conditioning in the normal matrix, and next an biased estimation based on ML_TSVD is proposed in this paper. Through theoretical analysis and computer simulation, it is proved that the algorithm can effectively improve the accuracy of the multipath estimation in high noise environment, so as to improve the anti-multipath performance of the code tracking loop.Recently, many satellite navigation systems including modern GPS will adopt a new modulation signal-BOC modulation signal. Unlike traditional BPSK modulated signal, the correlation function of BOC modulated signal has the characteristics of "multi-peak" and"tracking ambiguity" and this will brought new challenges for multipath suppression. On the basis of analyzing the principle and characteristics of the BOC modulated signal. We find traditional anti - multipath algorithm's performance is reduced and ambiguous problem is introducetd. This paper proposed a new non-coherent unambiguous anti-multipath algorithm based on S-curve shaping technique. And detailed analysis of the algorithm's performance proved that the proposed algorithm can not only eliminate the ambiguity problem but also improve the tracking loop's anti-multipath ability.