Research On Key Techniques Of GNSS Receiver With Antenna Arrays

Using antenna array GNSS receivers can obtain the abilities of spatial signal processing,efficient interference and multipath mitigation,flexible beam steering control,high signal gain and many other advantages,compared with the traditional single-antenna receivers.It can be seen that antenna array will be more widely used in the national economy and military applications.However,in some typical antenna array based GNSS receiver applications there are still many engineering problems urgently to solve,such as optimal environment parameters selection for surveying receiver installation,initial DOA estimation at cold start,GNSS signal DOA tracking when mounted on a mobile platform,detection and localization of the interference source in the complex electromagnetic environment and so on.Therefore,study on the key technology of GNSS receivers with antenna array has important theoretical significance and engineering application value.In this context,the thesis carries out the related research work from four aspects,and some contributions are as follows:?1?For the planar antenna array-based GNSS receivers for surveying application,as the beam pattern of a plane array is symmetrical about the horizon,the antenna array will also steer to the symmetrical multipath with a negative elevation angle when using conventional beamforming methods.Such multipath can seriously degrade the pseudorange measurement accuracy of the GNSS receiver.In order to meet the multipath mitigation performance of the system requirement,many existed researches focus on optimizing the antenna pattern to reduce the received multipath amplitude.However,the measurement error induced by multipath is not only related to the multipath amplitude,but also the relative time delay between the multipath signal and direct signal,so we can control the environmental parameters of antenna array installation to reduce the multipath measurement error.In the second chapter,based on the accurate modeling of the array antenna installation environment,the constraints of the multipath mitigation performance on the parameters of the installation environment are obtained in analytical form when using the narrow correlation technique and the Double-delta technique respectively.Results show that when there are multiple intersection points between the multipath error and the peak envelope curve,the installation parameters should be chosen so that the multipath error lies within the first intersection and the slope angle should be set within[ 40°,45°],,which will provide quantitative guidance for the antenna array-based GNSS receiver installation.?2?DOA estimation in the GNSS receiver with antenna array is usually implemented after the PN code and carrier synchronization.The main drawback of this method is that the GNSS signal acquisition performance cannot be improved by the beamforming ability of the antenna array.Aiming at overcome the shortcomings of existing methods,the third chapter proposes a joint estimation method of PN code and DOA based on MMSE criterion in initial phase of signal synchronization.The proposed method can achieve PN code synchronization and DOA estimation simultaneously,which significantly improves the signal parameter estimation performance of the GNSS receiver with array antenna at cold start.Simulation results show that the DOA estimation error will decrease as the input SNR is increased and the number of local PN code phase decrease,and when the SNR and the local PN code phase are-14 d B and 9 respectively,DOA estimation error will be better than 4.Meanwhile,in order to improve the convergence performance of the proposed algorithm at low SNR,a multi-correlator architecture according to MMSE criteria is implemented and verified.?3?Generally,the steering vector of signal DOA in body frame will change along with the attitude of the antenna array platform.In order to make the main beam of the antenna array based GNSS receiver mounted on a moving platform keep steering to the DOA of the GNSS signal,the DOA tracking method using direction lock loop is studied.Next,the performance is analyzed in detail as follows: the implement of angle discriminator,the output curve,the discriminator gain and convergence range.Then,DOA tracking with direction lock loop is verified under several simulation scenarios.However,the main drawback of the conventional direction locking loop is that the discriminator output will be a biased one when the DOA is not 0.In order to provide an unbiased tracking result,a real-time error correction method is proposed,which does not need any pre-correction and initialization.Simulation results show that under the simulated conditions the RMSE of the direction lock loop with the proposed real-time correction is usually not more than 0.1°.?4?Interference detection and localization are very important for GNSS users with high reliability and integrity requirements.To overcome the disadvantages of the existed interference detection method such as energy method which is sensitive to the noise power,the eigenvalue-based interference detection method for GNSS receiver with antenna array is introduced.The detection statistic is based on the ratio of the largest eigenvalue to the smallest eigenvalue of the sampled covariance matrix which has the advantage of independent of the noise power.Next,the analytical expressions of the probability distribution function under different test conditions and the threshold settings of the interference detection statistic under the condition of constant false alarm probability and constant detection probability are derived,respectively.Subsequently,the performance of eigenvalue-based interference detection method is analyzed and verified by simulations,results show that when the antenna elements number is 4 and data snapshot is 50,the probability of missed detection can achieve about 10^-4 while the probability of false alarm is 10^-4.For the localization of the fast moving interference source,a DOA estimation method based on the low complexity subspace tracking algorithm is presented.Simulation results show that under several typical trajectories stable DOA tracking can be achieved with this method,and under the simulated conditions with a 10 d B the interference-to-noise ratio the DOA tracking error is about 0.2°.Finally,the research results of the full thesis are summarized,and the future work to be carried out is discussed.