Research On Pseudolite Positioning Technique

Global navigation satellite system (GNSS) is a space based wireless positioning system. Anywhere on the earth, whenever the user received signals of GNSS satellites perfectly, the user always can located himself. However, the navigation signals from satellites are easy to be obstructed by the buildings, tree, wall and so on. In some situations, such as urban canyons, positioning in valleys and in deep open-cut mines, because the navigation signals usually are not able to be received, it will bound the application of satellite navigation technique more or less. Now, this problem can be solved by a new navigation technology that is pseudolite positioning technique.Pseudolites have many advantages, such as strongly anti-jamming, flexible configurations and low cost. It is established that the Pseudolites can increase the number of satellites and improve the geometric strength of positioning solutions. And the usage of pseudolites can enhance the accuracy, integrity and availability of GNSS. It also can extend the application field in which is not possible with satellite-only GNSS, such as city valleys and indoors.Preliminary research in this thesis was funded by the Shanghai Academy of Spaceflight Technology in 2009. On the basis of the preliminary research of the project, the objective of this research is to study the pseudolite positioning technique, and to analyze the key to the problems about pseudolites applications. Furthermore, to meet the requirements of navigation, a carrier phase differential pseudolite measurement model was given in the research. The emphasis in this work has been placed on:(1) In this research, the principle and structure of pseudolite signal were analyzed. The navigation message for pseudolite has been improved, because we want to get the measurements from an ordinary business receiver that received signal of pseudolites. Based on these researches, a design of practical pseudolite generator has been presented. The schematic and individual modules are also be proposed, this will succeed to a series of work from baseband to the upper frequency conversion.(2) It is as same as GPS that the measurement model of pseudolite positioning system is nonlinear. Linearization is a necessary step of most positioning algorithms for the nonlinear model. Because distances between pseudolites and rovers are shorter than those in conventional GPS positioning scenario, effects of linearization on positioning algorithm may not be ignored under some conditions. Through geometrical analysis, bounds of linearization bias in these systems are given exactly. Then, the effects of linearization bias on accuracy of positioning algorithms are discussed in different noise environments. Furthermore, based on differential geometry theory, a simplified criterion is proposed to evaluate the convergence of Gauss-Newton method for nonlinear least squares (NLLS) in pseudolite positioning systems. Finally, we propose a new algorithm to improve the traditional EKF. Simulation results validates that the algorithm is robust.(3) The characteristics of pseudolite positioning system are different from GPS, such as structure of system, signal and configuration. So, there are many problems that we met in pseudolite positioning system are not same as in GPS. Some key issues in the application of pseudolite, such as pseudolite synchronization, near-far effect, DOP and multipath problem were discussed in detail. And, depended on the different conditions, the method for these problems were presented.(4) A carrier phase positioning algorithm for pseudolite-only positioning system was studied in the research. The ambiguity resolution on the fly for the pseudolite-only positioning system is discussed in depth firstly. To get the floating-point, a floating-point filter architecture in terms of the CDGPS algorithm was designed. Simulation results validates that the method is robust.(5) According to the requirements of the project, an indoor pseudolite-only positioning system was designed. Control program of it is also presented. Finally the method for precise calibration of pseudolite antenna phase center is studied.