Study On The Reference Station Network Based Error Analysis And Modeling For Virtual Reference Station Technique

The Virtual Reference Station (VRS) concept is one of the most latest promising concept, in a broad sense of using multiple reference stations, which is applicable for centimeter-level accurate differential GPS positioning in real time environment. To create a VRS i.e. a reference station near by the rover receiver, the task concentrates on simulating a series of reference data, including both the accurate position and the GPS carrier phase observables, based on the benefit of using all of the observed information. As opposed to the conventional single station applications, e.g. RTK, Multi-Base methods or VRS technique lead to substantial improvements for positioning and navigation on the accuracy, service area coverage and system robustness. The error sources wrapped in the carrier phase observables are better modeled and reduced, which results in performance improvement in ambiguity resolution in real time.The basic theories of Virtual Reference Station are presented and the analysis and modeling of system errors is introduced as one of the most important part of VRS technique. Then theories involved in the main error sources, primarily the ionosphere errors, troposphere errors, orbit errors and multipath errors, etc. are under discussion. The ionosphere errors are selected for the research purpose and the pivotal techniques for the error calculation and parameterization of carrier phase corrections for ionosphere errors are stressed in order to reduce and eliminate the double-differenced ionosphere residual errors. Further more, the precision and reliability of the VRS technique is discussed, from the aspect of its effect on modeling and reducing the systemic errors.Based on the information fusion of all reference data, this paper studies the characteristic of both the ionosphere delay errors and its double-differenced residual errors over the network coverage area. To access the spatial correlation of the ionosphere or double-differenced ionosphere errors, a parameterization model of carrier phase correction of the distance-dependent ionosphere errors is created, using the pre-calculated double-differencedionosphere errors on the baselines between the reference stations. Finally the above model is applied in VRS technique to generate the local simulated error correction for the user.Field experiments data are used for the study on the modeling of the ionosphere errors and related calculation, after which results validation and relevant conclusion are summarized.