Research On Multipath Mitigation Of GNSS Receiver

Global Navigation Satellite System(GNSS) are widely utilized by many fields due to GNSS has advantages of global coverage, all-weather, high efficiency, automation and high precision services of positioning, navigation and timing. However, the major source error of GNSS signal includes orbit error, satellite clock bias, ionospheric delay, tropospheric delay, multipath interference and so on. Above errors severely degrade the positioning accuracy of GNSS receiver. With the development and modernization of GNSS, most of error types can be abated by revised model and differential system except multipath error. So the multipath error is dominant in source error.The multipath effect refers to the receiver not only receive the direct signal, but also the reflected signal. Multipath effect usually exhibits different characteristics in different conditions and different times. Due to closely related to the current condition that the receiver is located, the multipath error cannot be eliminated effectively by utilizing the differential technique, thus it becomes one of the major factors which restrict the positioning accuracy of satellite navigation system.Researches on the mitigation technique of GNSS receiver, the main content of this paper are as follows:1. Introduces the features of multipath signal of satellite navigation system and the formation mechanism of multipath effect. Then separately establishes the multipath model under static condition and dynamic condition. At last, focuses on the mathematical model of the receiver code tracking delay lock loop(DLL) and deduces the influences of multipath interference on the GNSS receiver code tracking loop and carrier tracking loop detailedly.2. Analyzes the current multipath interference mitigation techniques which mainly include Narrow Correlator, Strobe Correlator, and Multipath Estimation Delay Lock Loop, and discusses the advantages and disadvantages of these techniques. The paper presents a multi-correlator multipath estimation technique which based on the maximum likelihood estimation technology, and simulates the estimation performance of the algorithm under noise free condition and AWGN channel condition respectively. The simulation results show that the algorithm can estimate the feature of direct signal and the multipath signal, such as the code delay, the amplitude, under a higher SNR condition.3. Aims at the defects of the existing multipath mitigation techniques, especially they are hard to eliminate the short delay multipath interference, the paper presents a short delay multipath interference mitigation algorithm which has Multipath Insensitive Delay Lock Loop(MIDLL). The algorithm analyzes the correlation model under multipath interference, introduces the discrimination function of MIDLL detailedly, and studies on the discrimination function of MIDLL under different RF front-end filter bandwidth. Simulation results and analysis show that MIDLL can improve the performance of tracking error when multipath interference is fluctuated dramatically, and tracking error can be limited to 1 m on pseudorange in typical multipath environments.