Research On Evaluation Methods For Multi-GNSS Data Quality And Integrity

With the development and improvement of GPS,GLONASS,Galileo and BDS,the global satellite navigation system has entered into a multiple system co-existence era.As raw GNSS(Global Navigation Satellite System)observation data was one of the most important information for positioning,real-time decoding and quality analysis of raw GNSS data stream is the premise and foundation not only for the establishment of multi GNSS fusion function and stochastic model,but also for the improvement of accuracy,reliability,effectiveness and continuity of positioning in the multiple system era.Taking into account the actual needs for high-precision positioning,a study of data quality analysis and integrity evaluation for multi GNSS which is compatible with GPS/GLONASS/Galileo/BDS is conducted in this paper.The main research contents of this paper are as follows:(1)The error sources and influence in GNSS observation equations are analyzed.Basic knowledge of GNSS positioning is introduced in detail which included signal types consistsing of carrier phase,ranging code and data code;GNSS pseudorange and carrier phase basic and double difference observation equatios are introduced and the error terms in the equations are analyzed;According to the different categories of sources,the errors appearing in the processing of GNSS positioning are illustrated and analyzed,especially the bigger errors.(2)Design and realize the decoding method of mainstream GNSS data formats.The development,structures and applications of each main GNSS raw data formats are introduced in the paper.By analyzing the formats and checking algorithms,the characteristics and applications of different GNSS raw data formats are presented.Decoding methods for different formats are put forward in this paper,and the function of realizing decoding in real-time as well as after the event.The accuracy of results are compared with that of commercial software,and the results showing that the difference of pseudorange varies in ±0.001 m and the difference of carrier phase varies in ±0.005 cycle.(3)The factors affecting the GNSS observation data and their analyze methods are expounded.Data quality indicators,such as DOP,multipath effect,ratio of signal to noise,data integrity are studied from the aspects of constellation availability,environmental impact,receiver performance and the loss rate of data.Many indicators have a relationship with satellite altitude angle during the research.More satellites could be observed by appropriately reducing the threshold value of satellite altitude angle and constellation space geometric distribution structure can be better;Satellite observation data quality of high altitude angle will be better in the condition of enough satellites observed;According to these indicators,three groups of data are chosen to analyze and a reference results are given.(4)GNSS signal evaluation and receiver noise detection method are proposed.Receiver internal noise is an important factor affecting the quality of GNSS observation data.One of the zero-base tests is chosen to analyze the relationship between observation residuals and satellite altitude angle,and a conclusion came from it which the higher the altitude angle,the smaller the observation residuals.By comparing the observation residuals of different systems and different types of satellite,a conclusion that signal precision of Galileo system affected by the receiver noise is minimal,while signal precision of BLOCK IIR satellite in GPS system affected by the receiver noise is maximal.Finally,by analyzing the 3-D coordinate increment of four sets of zero-baseline data,the noise level of four different types of receivers under different baselines is compared,and the influence degree of the distance measurement signal is also given.