Vector Tracking Technique For GNSS Receiver In Challenging Environment

With the development of the Global Navigation Satellite System(GNSS),the GNSS receivers are widely used in more and more field,especially in the challenging environments,and many researchers pay attention to improve the usability and other performance of the GNSS receiver in this condition.The tracking processing of the GNSS signal is a key part in the receiver design,and vector track loop(VTL)as an advance tracking technology for the GNSS signal has been received more attention recently.This paper studies VTL for the GNSS receiver to improve its performance in the challenging environments.Firstly,based on the model of VTL,some modify and paramenter optimization techniques are studied.Then the detail application of VTL for the modern and intermittal GNSS signal are studies.In the aspect of the VTL model consummation,the main work and innovations includes:(1)In the conventional VTL,the position,velocity and time(PVT)information of the receiver are feedback to each signal tracking loop to improve the performance,but this mapping is a rank defect processing,so the VLT has non-uniqueness convergent results,and will result in the tracking bias.This paper proposes a robust vector tracking loop based on a diagonal weighting matrix to eliminate the rank defect mapping while feeding the PVT information back to the signal tracking loop,so this technique makes sure the tracking result unbiased.(2)The VTL computational burden is mainly impacted in two factors,one is the computation during the tracking loop updating once time,another is the update interval of the neighborhood twice trakcing loop.Without changing the first factor,prolong the update interval can reduce the computation burden within the unit time,but the long update interval can also reduce the dynamic performance of the tracking loop.So the update interval need to been optimized.This paper proposed an optimization model of the update interval to obtain the lowest tracking threshold of thracking within the given signal dynamic.To the BDS B1 I signal,analysis and optimization results show,when the maximal dynamic is smaller than 0.1g,the update interval can be prolonged to 0.3s and its tracking threshold is lower as 20dB-Hz.Compared with the update interval equals to 20 ms,the computation burden within the unit time of the optimizal VTL is smaller.In the aspect of the application of the VTL in different types of signal,the main work and innovations includes:(3)The modern GNSS signal contains a data component and a pilot component.The pilot component does not modelate the navigation message sign,so it has higher tracking performance in the challenging environment.The VTL can track the signal carrier frequency and code phase,but usually need the assist of the scaler tracking loop while tracking the carrier phase.In consideration of the characteristic of the modern GNSS signal,a robust multiple update-rate Kalman filter(RMUKF)is proposed and used to combine the different update-rate discriminator results in one tracking loop.With the help of a three-segment adaptive factor,the RMUKF can adapte the contribution of different discriminator results to the tracking loop and improve the its robustness.The simulation and test results show,the RMUKF can tracking the GPS-L5 signal when the signal power is as lower as 13 dBHz in the indoor environment.Furthermore,based on the RMUKF,a vector and scalar hybrid tracking loop(HTL)is proposed.In the HTL,the vector tracking loop outputs and the discriminator outputs are used as the inputs of the RMUKF,and the RMUKF adjusts the contributions of the VTL outputs and the discriminator outputs to the final tracking results.When the singal is lower,the results of HTL is mainly depended on the VTL outputs,and when the signal is higher,the results of HTL is mainly depended on the scalar tracking results,so HTL can tracking the signal carrier phase steady.(4)The intermittent GNSS signal is usually existed in the low-power GNSS baseband chips.To process this type signal,the conventional scalar tracking need a long time to keep its result convergence,and it is sensitive to the initial trakcing errors.The conventional open loop has a worse tracking precision.In this paper,an open Kalman filter is proposesd to tracking the intermittent signal.Based on the open loop structure,this algorithm firstly get the coarse result of the signal carrier phase,carrier frequency and code phase,then use a Kalman filter to improve the preciser results.Furthermore,the open Kalman filter algorithm is extended into a vector structure,and an open vector tracking and position technique is proposed to process these intermittent signal.In the open vector tracking and position algorithm,the open loop outputs are as the input of a intermittent Kalman filter to get the PVT informance directly,and there is no need the conventional observation for the conventional PVT solution.The real data processed results show,this technique can process the signal whose duty cycle is lower as 2%,and the 95% position precesion is about 11.4m.Finally,the main works of this paper are summarized,the engineering applications are introduced,and the future works are presented.