An Adaptive Multipath Mitigation Technique Research Based On BP

In recent years, the GNSS has been extensively applied to affording intact and exact orientation information for users. However, the multipath errors, troposphere error, ionosphere error and orbit error are the main error sources which restrict the elevation of GNSS navigation and measure precision. The last three errors are system errors, which can be eliminated by modeling and diffiential system, but the multipath errors can not be eliminated by diffiential method. Hence, how to improve the orientation precision in multipath environment has been an important research problem for GNSS.Based on the spread spectrum communication theory, this paper analyses the spread spectrum code tracking error. Moreover, the existing multipath interference suppression methods are simulated and analyzed in this paper. The shortcomings of these methods are indicated as well. According to the multipath estimator based on BP method, this paper proposes a multipath interference suppression method based on BP method, and this method is realized based on FPGA. The major works of this paper are as follows:Firstly, the working principle of GNSS receiver tracking loop is analyzed, and the PN code tracking error and carrier tracking error are deduced and simulated based on it. These researches establish the foundation for performance analysis of multipath interference suppression methods.Secondly, the narrow correlation technology, MEDLL, CADLL and Cross Correlation Function-Analysis(CCF) are analyzed. The advantages and disadvantages of these multipath interference suppression methods are gotten by comparing the simulation results and the problem of short delay multipath error elimination, which need further improve, is indicated.In order to improve the performance of short delay multipath error elimination method, an adaptive multipath error elimination method based on BP learning algorithm is proposed in this paper. The new method estimates the three parameters which are amplitude, time delay and carrier phase through adaptive linear cell, reconstructs the multipath signals, and eliminates them from overall receive signals, thereby gets the correct correlator cost of nonstop signal. The simulation results show that the new method proposed in this paper can primely eliminate the multipath interference, and has higher tracking precision in short delay multipath interference condition.At last, the signal correlation circuit and Nios II soft core processor are designed in FPGA based on the above mathematic model. The design of tracking demodulation circuit is also realized in FPGA. Moreover, the design of adaptive multipath interference suppression method based on BP algorithm is realized in Nios II, and the simulation results is given in this paper.