Research On Key Issues Of Multi-GNSS Hybrid CORS Network For Real-time Location Service

With further research and applications, many industrial and regional CORSs, for instance, Crustal Movement Observation Network of China (CMONOC) and provincial CORS network, have been established and covered in most parts of China. Obviously, CORS has formed a vital part of Spatial Data Infrastructure (SDI), and also sparked a new wave of wide-area real time location service research. Due to differences between the application purposes, different CORS networks have various establishment standards for GNSS hardware, internet communication network, etc. Therefore, hybrid of different CORS networks is rarely adopted in practical application for real-time service represented by network RTK (NRTK) service.In recent years, BeiDou Navigation Satellite System (BDS) has been continuously developed, and more than 25 satellites, consisting of GPS/BDS/GLONASS system, can be observed currently in the Asia-Pacific region. Due to the consideration of observation quality and positioning coverage, some of CORS have been updated to BDS compatible receivers, while others have not been updated due to cost and application purpose. The various qualities of CORSs impose more difficulties to real-time location service.With approaching of the Internet of Things (IoT), the need for decimeter-level and centimeter-level precision location service for wide range and massive users increases intensively. The State Council announced, in the medium-term and long-term national satellite navigation industry development plan, that the scale of national satellite navigation industry will exceed 400 billion yuan by 2020. It becomes imperative to integrate existing CORS resources to meet industry demands.However, there is no effective management program for all CORS stations; meanwhile, the performance of existing NRTK service products is not satisfactory in the diversity receiver and antenna, communication and the application of integrational observation network in complex environment, and there are still some inadequacies in compatibility of BDS NRTK service. Relative issues still need further research.In order to adapt the current development of GNSS location service industry and to improve the applications of BDS/CORS NRTK service, some key issues of multi-GNSS hybrid CORS network for real-time location service will be deeply discussed in this dissertation, relating to GNSS observation models and errors analysis, integrational network construction and resolution, VRS technology and the performance monitoring of GNSS/CORS network location service. And some useful and helpful results are achieved.In conjunction with the current development of constellation system, GNSS real-time location service and domestic GNSS observation network, this dissertation elaborates the existing conditions of the implementation of multi-constellation observation network location service; On the basis of the current requirement of Chinese GNSS technological innovation and industrial upgrading, this paper explains the practical significance of multi-constellation CORS observation network; Apart from these, the current status and weakness of the related researches is summarized in the beginning.The multi-GNSS observation model and its linear combination are elaborated; Based on the geometry model, a new model is proposed for relative positioning resolution, with the feature that its coefficient matrix remains unchanged in the resolution process, and thus, the computing of multi-constellation GNSS relative positioning are more effective compared with the traditional model; And also, the properties of spatial and non-spatial distance related errors are described and the algorithms for removing or mitigating these errors for centimeter-level RTK positioning are explained in detail. It's worth mentioning that even in low-latitude areas, the double differential ionospheric delay is only about 1IDU between 12 pm to 8 am, which could be ignored in wide-lane combination; this feature helps processing frequency related errors such as hardware delay, multipath delay and so on.In process of network construction, considering with the difference of available constellations among CORS stations, this paper proposes the idea that integration network construction and VRS observation calculation should base on satellite system, which could effectively avoid the generation of blind area for each constellation. And an algorithm for calculating precise coordinate of new station is proposed based on spatial dependent corrections of GNSS/CORS network resolution, it can be used to improve the coordinate resolution efficiency combined with the central differential positioning technology, thus accelerating to encrypt CORS networks and improving the service quality of regional RTK. Meanwhile, an evaluation factor for network structure is proposed, against the spatial error correction, it can be used for evaluating the structure, and to be a theoretical and practical indicator for optimizing CORS network and evaluating NRTK service's performance.For network solution, a method for rapid determination of wide-lane ambiguity is proposed based on the synthetic error correction model of wide-lane combination. For CRTN, JDCORS and HKCORS, representing the mid-latitude coastal areas, mid-latitude inland areas and low-latitude areas respectively, several experiments have been conducted. The result shows that the interpolation precision of the synthetic error of wide-lane combination is better than 0.3 cycles. As a result, only a few stations are necessary to interpolate the synthetic error in the regional CORS network. In addition, disturbances of pseudorange multipath and GLONASS pseudorange inter-frequency bias in partial stations could be mitigated effectively for network resolution. Thus, the proposed method can improve the efficiency and reliability of GNSS/CORS network resolution, reduce the quality requirement of pseudorange of other stations, and reduce the cost of GNSS/CORS network construction significantly.This paper also puts forward a service pattern of virtual single station network (VSSN), which can be compatible with the ordinary single base station applications and can be used to the high-precision location service for massive users. JDCORS and HKCORS are analyzed respectively. The result shows that the distance between two VSSNs can up to 3km (north-southern direction),4km (east-western direction), and 0.2 km (north-southern direction),2km (east-western direction) respectively. Therefore, a small number of VSSNs are required to meet the demand for services.Furthermore, combination with the time lags analysis and the morphology filtering, this paper proposes a method to predict triple difference residual error, which can be used to monitor the effects of surface deformation imposed on CORS network location services coordinate frame. Partial stations'data of GNSS observation network has been employed during the 2013 earthquake in Lushan, and the result represents that the proposed method can quickly detect the CORS station's deformation with high precision, better than 10mm in horizontal and 20mm in vertical.In the final part, two systems, including a station management and service system and a NRTK service system (VENUS) are introduced respectively. And, experimental results show that VENUS has equivalent performance with GPSNet and GNSMART in GPS+ GLONASS service, while the fix rate of rover increases significantly in complex observation environments when combining BDS. At the same time, the result proves that the positioning quality of BDS NRTK service is similar with GPS.