| With the increasingly harsh electromagnetic interference environment GNSS is faced, anti-jamming navigation receiver plays an increasingly important role. It takes advantage of spatial interference suppression technology to effectively avoid interference and improve the signal to interference and noise ratio, thus contributing to the baseband signal processing of the receiver signal, like acquisition, tracking, position calculating. However, in practical applications, the anti-jamming performance of DBF is affected by channel mismatch. In order to ensure navigation receiver immune from interference, the requirement of array calibration becomes more urgent. In this paper, focusing on the theme of channel mismatch of GNSS adaptive array, plenty of in-depth studies have been launched, attempting to find the appropriate methods for array calibration which make fit with navigation receiver characteristics. The main work and the details are as follows:1. Study the characteristics of the channel of satellite navigation receiver, finding that inconsistency of antenna is important part of the channel mismatch and can not be ignored. Also study the conventional methods for array calibration or channel equalization, and find that they only consider the mismatch of RF front-end part in channel. Therefore, we must study the methods of calibration for GNSS adaptive array.2. First, three different norms concerning interference suppression are set to evaluate the performance of anti-jamming, finding that the channel mismatch results in performance deterioration: reduce the of zero depth in array pattern, reduce the degree of interference suppression(AJ), and the second peak to peak ratio in acquisition. Then study the effect of channel mismatch has in the satellite signal, finding that to Non-ideal frequency characteristics of the channel will cause step size of pseudorandom code chip change, code phase delay, thereby causing distortion of correlation peak. Finally, the theory is derived through channel mismatch results in distortion in correlation peak changing with the weight vector in DBF, which means the code delay measurement error can’t be measured easily.3. Channel mismatch in narrowband form is modeled, and a new array calibration method for GNSS adaptive array is proposed. This method takes advantage of the ability of receiver to providing position information, the characteristic of satellite signal self-correlation and orthogonal projection principle, achieving channel consistency without the additional calibration source. First, theory of this new method is analyzed, and then the feasibility of it is verified by simulation, in the same time analysis of the impact of SNR and the correlation time T on the performance of the method is discussed. Finally tolerance issue is discussed. Where the error of prior information, direction of satellite signal, can be stem from is analyzed, and the impact of the maximum possible error in direction of arrival on the feasibility of the method is verified to be small.4. Channel mismatch in wideband form is modeled, and a new channel equalization method for GNSS adaptive array is proposed. The important part of this method is the online estimation of channel frequency response. It takes advantage of correlation of received satellite signal with the local reference signal and frequency response in Taylor series expansion mode, solves equations of Taylor series coefficients through least square and achieve online estimate. LFM signal is not needed in the new method as auxiliary calibration signal. After obtaining the frequency response of each channel, an inverse Fourier transform algorithm is used to equalize the channel mismatch. Firstly, online estimation algorithm is verified to be useful, and two factors are analyzed concerning their impact on performance of estimation. The inverse Fourier transform equalization algorithm is also verified. Finally, analysis of code delay estimation error after channel equalization is executed. |
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