Real-time Kinematic Positioning Service Mechanism Of Combined CORS

The CORS application field shows the development trend of―extensive construction‖and―real-time service‖in domestic and overseas. Based on the existing specialty-oriented, region-oriented Independent CORS (iCORS), by interconnecting adjacent iCORS, a higher level and larger scale of Combined CORS (cCORS) can be formed which has a considerable number of base stations. It offers not only basis static positioning services, but also a wide range, high dynamic, high precision and real-time kinematic positioning services. To break the current situation of region segmentation, independently-operating of the iCORS and achieve a smooth transition to the trans-regional, cross-trade, inter-agency cCORS, we need to use new ideas and technology to establish a new data processing and service supply models, and promote all kinds of interconnection, interchange, and interoperability of iCORS, in addition to integrate all aspects of needs, develop appropriate standards system, increase the density of stations. Through research on grid computing applications of earth science (especially geodesy), it is found that the grid computing technology can effectively solve the bottlenecks of CORS, such as heterogeneous, interoperability, resource management, service virtualization, etc. In this paper, based on the technology of Web Services (WS) and the Grid Services (GS), the mechanism of kinematic positioning services for cCORS is researched, mainly including:(1) Model of positioning user demand. The service type, service content and positioning technology of cCORS user community are analyzed in detail. The applications, accuracy requirements, time availability and validity of various types of positioning technology are summed. Finally, cCORS service pedigree and user detailed requirement are obtained. By Analysis of the impact of the user demand diversity on the system heterogeneous, the paper put forward the―demand inclusiveness, logic restructuring‖solution. It proposes and defines a tree structure user demand model, with content of domain, type, attributes, values, entries. It gives a reasonable semantic description. It establishes the mapping mechanism of user demand model. The mapping relationships among the domain, type, service scene and business processes are detailed defined. A user role model is proposed, and the correspondence between user groups and positioning service scenarios is further clarified.(2) The cCORS architecture. From four perspectives of the protocol specification, hierarchical structure, physical structure and logical structure, the cCORS system structure is established based on WS and GS, with the center of professional computing and comprehensive service. The protocol-oriented hierarchical structure is established, composed by the Internet protocol suite, XML protocol suite, Grid protocol suite, GNSS protocol suite and GNSS application interface standards. The service -oriented hierarchical structure is established, composed by the foundation layer, communication layer, service layer, business layer and application layer. A "physical scattered, logical focused" loosely coupled distributed architecture is given, which can integrate existing iCORS and ensure their autonomy, and handle computing tasks across multiple processing nodes. Two types of service-oriented logical structure are proposed, one is post-positioning online service system, the other is kinematic positioning online service system. Their specific logic and process workflow are also given respectively. Considering the cohesion and coupling of algorithms, the system structure of meta-services and advanced application services is built, and the building principles, hierarchical structure, functions list, and deployment method are given.(3) Theoretical model of Grid computing. A theoretical model, named Parallel Multi-type Computer with Active Memory (PM-CAM), is proposed, with extended instruction set and semantic set. PM-CAM is used to study some problems, such as Grid protocol and mechanism, Grid program's algorithm design and complexity evaluation, Grid service communications and resource scheduling, Grid service quality evaluation, etc. The mapping relationship between the model and the grid framework is elaborated. By analyzing the instruction stream instances of user kinematic positioning services, the feasibility of the model applied to the complex description and performance expression of cCORS is proved. Thus, the model provides effective theoretical guidance for following software design and deployment.(4) Data characteristics analysis. Aiming at the problems of data's diversity and heterogeneous, the solution of data structuring and virtualization is put forward. The impact on the cCORS data acquisition, data processing, positioning services and a series of processes is analyzed, caused by increasing of the general GNSS multi-mode multi-frequency data sources. The requirement properties of the distributed sensor networks formed by CORS stations, such as parallelization, distribution, coverage, connectivity, fault tolerance, and many other features, is explained. Several protocol standards closely related to the CORS positioning services, being used in data collection, storage, remote transmission and other occasions, is analyzed. In view of the problems between each iCORS, such as different standard of construction, disunity of geodesy datum, different data format and observation interval and other issues, the mechanism of data real-time aggregation and integration is built, and gives evaluate method to access the data transmission quality indicators, based on the buffer pool and thread pool technology.(5) The mechanism of data collection and distribution. The transmission quantity of original observation data and kinematic difference service data is calculated and analyzed. The real-time data collection and distribution mechanism, such as parallel transmission, fault-tolerant transmission, parallel fault-tolerant transmission, distribution transmission, congregate transmission and others, is studied. Aiming at the non-deterministic network connections environment and the complex multi-stream data flow and other conditions, the CORS Streaming Data Service (CSDS) protocol is designed, as well as the data transmission services'encapsulation and deployment for four application scenes, which proves that CSDS can better adapt to cCORS complicated data communication link. The acquisition, integration and distribution system for the generalized GNSS multi-mode multi-frequency observation data is established, enabling that any data collected by stations can be simultaneously accessed by multiple computing nodes, forming a cross-regional multi-node parallel interconnection mode. Facing the complex network topologies formed by a variety of interconnecting ways, such as the central interconnecting, central integrating, stations sharing and stations relaying, etc., data transfer optimization scheme is put forward in the application level. After establishing the layered covering mechanism for cross-domain transmission, the corresponding optimization service method is proved. In order to enhance the reliability of data transmission link, the Modified Proactive Approach Algorithm (MPA) is proposed, which can be used in tree reconstruction for the backup link and the establishment strategy of tree reconstruction is analyzed.(6) System heterogeneity and virtualization technologies. In view of systems heterogeneous, information heterogeneous and service model heterogeneous, a detailed analysis of cCORS heterogeneous problems is given. Then, the dynamic, autonomy and dichotomy properties are studied, and resource management challenge is pointed out. According to reusable features, replicable features, mobile features and management logic features, the resources in the cCORS are classified. The development of the technology is pointed out, with expanding service sector, the diversion of resource's types and functions make resource synergy more and more difficult. In response to these challenges, a―resources virtualization‖and―services standardization‖solution is proposed, that is, using integration of resources and services by virtualization technology, based on the existing WS and GS protocol specification, to realize services standardization and provide on a common interface for all service deployed in resources, thus achieving resource management and service cooperation, and supporting complex web-based GNSS applications. On analyzing technology development condition of WS and GS, WSRF is used to achieve cCORS integrated management of resources and services, and WS-BPEL is used as orchestration language of cCORS service composition and workflow. (7) Resource management and service mechanism. Two kinds of resource management method is proposed, and a cCORS resources management mode is established. A 4-part registration center is designed composing of the proxy, registrar, manager and database. A two-layer service composition method is given, that applied to the WS/WS-R organization and WS-BPEL orchestration respectively. According to resources layer, service layer, composition layer and demand layer, the cCORS services logical structure is designed. In term of the service resources matching, the concept of mapping service set is proposed for single service selection, and the concept of services combination adapter for multiple services selection, which can enhance the matching adaptability.(8) Kinematic positioning service technology based on virtual CORS (vCORS). The concept of vCORS is proposed. From the application layer, service layer and facility layer, its operation logic is described. From the establishment of meta-service system, management of life cycle, construction and optimization of network, automatic updates and switching mechanism of vCORS, QoS indicators and other aspects, the vCORS process of real-time kinematic positioning services is analyzed in detail. The automatic change mechanism of vCORS is established, the Service Event Policy Language (SEPL) is proposed and defined, and 8 kinds of typical change events is analyzed. Using SEPL, a standardized description of the change events'occurrence, capture and handling mechanisms is given, making change events directly relate to services. The evaluation method of real-time service quality of vCORS is discussed; user-oriented measurable business QoS indicators system is established. On the basis of analyzing the online high-precision post-positioning service system, the concept and realization method of the online high-precise kinematic positioning service system are put forward.(9) Software prototype. Facing cCORS real-time positioning service, a software prototype is developed independently. Under the simulation environment, for real-time kinematic positioning services, the software key prototype and algorithm are verified from six aspects, including user demand response, data transmission, service deployment, vCORS formation and destruction, service products distribution, product quality and other aspects. The correctness and rationality of some computing services are tested. The test results and conclusions are given with charts and figures, and the reliability and practicability of software prototype are verified.