Research On Pseudolite Dynamic Positioning Method And Its Enhancement Of GPS

Under the bad observation condition,the number of satellites and their geometric distribution observed are not precise enough to meet users' demand of precise positioning.The GPS receiver even can't work in extreme conditions. Meanwhile,affected by the factors such as delay error caused by troposphere and ionosphere,GPS doesn't have good vertical positioning accuracy with the error of 2～3 times of that in horizonal direction.Therefore,the pseudolite becomes an effective way to solve these problems.A relatively precise error model is built to educe the relation between location error and the pseudolite elevation angle based on analysis of the key issues and error in pseudolite locating in this paper.Then the dynamical positioning technology of pseudolite is analyzed and simulated.But pseudolite can't direct use linearizing pseudo range measure equation to do locating because of the conclusion that the effect of the truncation error during the process of linearization while dynamic filtering can't be ignored in pseudolite positioning in contrary to GPS through the analysis of nonlinearized effect factors of pseudo range measure equation.The Extended Kalman Filter(EKF) and Unscented Kalman Filter(UKF) method is proposed in the paper,and the simulated experiment of pseudolite-only positioning,pseudolite -mainly combined positioning and GPS-mainly combined positioning is respectively implemented to prove the advantage of EKF and UKF for dynamical positioning of pseudolite.Then the pseudolite's effect on performance growth of GPS is researched through theoretical derivation and simulation.On one hand,based on the research on pseudolite's effect on positioning accuracy of GPS,that the pseudolite could reduce the DOP value of satellites system is proved.And it's demonstrated that the change of the number of pseudolite and its elevation angle both have effect on locating as well as azimuth angle.Then how to choose the best satellites combination is discussed and simulated.On the other hand,the pseudolite's effect on availability of GPS positioning meeting the demand of perfect property is researched.And the fact that the pseudolite can reduce Vertical Protection Level (VPL) of satellite navigation system and improve availability of system is proved by the simulated experiment.