Research On Interoperability Algrithm Of Global Navigation Satellite System

The context of global satellite navigation is altering. The GPS monopoly time has passed, multiple GNSSs are coexisting now. Compatibility and interoperability has become the main means to safeguard the core interests of all GNSS providers. The worldwide major GNSS providers are using a variety of international occasions, maintaining their core rights and interests through compatibility and interoperability. Interoperability is one of the core contents of the current research of satellite navigation technology, and has become a hot spot and development direction in GNSS field, which make all major GNSS providers attach great importance to. The core content of GNSS Interoperability technology is to eliminate or mitigate the impact of the differences among systems. With the steady progress of Bei Dou’s construction process, a higher requirement of GNSS interoperability research is putting forward to us.The technology research foundation is formed by a series of projects, related to GNSS interoperability, led by China Satellite Navigation Office. The research direction foundation is made up from the technical discussion among Interoperability Sub-group in the Working Group A of International Committee on Global Navigation Satellite Systems. Under these two conditions, this paper mainly analyzes the difference between the system and its influence on the positioning results and users. These differentiation factors are separated into distinguish and structural differences, carrier differences and information differences. The discussions are for the purpose of designing reasonable and feasible methods not simply reducing negative effects from those differentiation factors to service performances, but also expanding their positive effects. This paper analyzed the following five aspects: generalizing the differences and their influence between GNSSs, GNSS time interoperability, GNSS coordinate interoperability, constellation of GNSS interoperability and algorithm of GNSS interoperability.Firstly, we combed the differences between GNSSs and classified these factors. Discussed and clarified the impact of these factors on the process of PVT solution. Combined with the GNSS Interoperability requirement investigation results of BeiDou, clarified the main research content of GNSS interoperability.Secondly, discussion in view of the GNSS time interoperability is putting forward. System time bias monitoring and forecasting is one of the main tasks of GNSS time interoperability. After introduce the reason of GNSS time bias, we analyzed the requirement of time unification and the feasibility of GNSS time interoperability. Next, the system time bias processing method in both user level and system level is discussed respectively. To deal with time bias forecast, we analyzed the quality and characteristics of GNSS time bias data, and discovered that time bias obeying power law distribution. After that, principle of using polynomial model, grey model and fractal fitting model to forecast time bias is discussed respectively. Then, through numerical experiments, the common used time bias prediction method is compared and analyzed.Thirdly, we discussed the GNSS coordinate interoperability. Because there is less difference on the earth surface in different GNSS coordinate system, many scholars hold the opinion that the system coordinate may not need to be converted to each other. We make the coordinate difference at the height of the satellite orbit as the starting point, analyzed the necessity of GNSS coordinate interoperability. It is difficult for normal users to obtain the official coordinate conversion parameters. We designed a method to solve the coordinate transformation parameters using the products of International GNSS Monitoring and Assessment service. Then, the effectiveness of the proposed method is verified by simulation results.Fourthly, GNSS interoperability takes the constellation complementarity to users, a quantitative analysis of this complementarity and its effect is processed. Taking GDOP as the research point, and combining with ranging accuracy change caused by the GNSS signal interference, we discussed the improvement of GDOP quantitatively. We found a special functional relationship between the average GDOP and the number of visible satellites. Then based on this special functional relationship and geometric model, the relationship between GDOP and the number of constellation satellites is discussed. Meanwhile, the non-existence of "GDOP saturated value" is proved.Fifthly, the positioning and integration algorithm of GNSS interoperability are discussed and simulated. Two kinds of positioning algorithms are analyzed, which are the results combination and the pseudo range fusing. We consider that the results combination is in fact a kind of multi-GNSS positioning mode, while the pseudo range fusing is the interoperability positioning mode. After that, we discussed the mathematical models of these two positioning algorithms, and analyzed the improvement of the performance in PVT services. Based on the traditional RAIM algorithm, a new algorithm for satellite fault detection and recognition for GNSS interoperability is discussed, which is employing the least square residual error method. The algorithm process of GNSS interoperability is combed and then the simulation calculation is carried out.The main conclusions of this paper are as follows:(1) The calculation results of the gray correlation degree show that the user is concerned with the high degree of mutual operation parameters;(2) The time difference data analysis shows that the system time difference satisfies the power law distribution and has self-similarity;(3) By calculating the coordinates of satellites in different coordinate system, it is known that the GNSS coordinate interoperability is necessary;(4) The simulation results show that there is a linear relationship between the square of mean GDOP value and the number of visible satellites;(5) The non existence of “GDOP saturation value” can be verified by the combination of the constellation of the interoperabled GNSS system and the compatibility analysis.