Subjects: Astronomy >> Astrophysical processes submitted time 2023-06-07 Cooperative journals: 《天文学进展》
Abstract： The Beidou-3 global satellite navigation system was officially opened on the morning of July 31, 2020. With the gradual improvement of the Beidou system and the continuous improvement of its accuracy, users have higher and higher requirements for the integrity of the Beidou system. The BDS-3 system uses the four parameters (SISAIoe, SISAIocb, SISAIoc1 and SISAIoc2) in the broadcast ephemeris to indicate the accuracy of the ephemeris and clock error parameters, but the four SISAI parameters have not yet been given user algorithms in the interface control document (ICD). The integrity service of the BDS-3 system cannot be applied in practice. This paper studies the level conversion algorithm and user algorithm of the basic integrity parameter SISA of the Beidou-3 system, and uses the International GNSS Monitoring and Assessment System global network data and SISAI parameters in the Beidou-3 satellite broadcast ephemeris in accordance with the integrity requirements of the International Civil Aviation Organization (ICAO) non-precision approach (NPA) and has conducted preliminary verification and analysis of the integrity and service performance of the BDS-3. The test results show that with the completion of the BDS-3 system and the SISA parameter algorithm adopted in this paper, the BDS-3 system’s NPA stage integrity service capability is 100%.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-06-07 Cooperative journals: 《天文学进展》
Abstract： Differential code bias (DCB) plays a key role in the generation and transmission of GNSS space-time information, and the characteristic analysis of DCB parameters is of great significance for promoting GNSS high-precision navigation positioning and timing application. Based on DCB products provided by Chinese Academy of Sciences (CAS) and German Aerospace Center (DLR), the average monthly stabilities of the GPS satellite intrafrequency bias, the GPS satellite inter-frequency bias and BDS satellite inter-frequency bias is analyzed, and the influence of different ionospheric processing strategies on the periodic characteristics of the inter-frequency bias is studied. The results show that the average monthly stabilities of GPS satellite intra-frequency bias products provided by the two analysis centers are less than 0.07 ns, the average monthly stabilities of GPS satellite and BDS satellite inter-frequency bias are less than 0.08 ns and 1.12 ns. The stability of GPS satellite inter-frequency bias is better than that of BDS satellite. Some satellites’ DCB(C1C-C2W) have annual and half annual periods, and the periods of the DCB(C1C-C2W) provided by CAS and DLR do not differ.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-06-07 Cooperative journals: 《天文学进展》
Abstract： The atomic clocks measure time by the stable frequency standard, and the output signal of the oscillators is easily affected by noise from different sources which makes the phase deviation between two atomic clocks obeying a continuous power-law random process. Such stochastic process is not stationary and a typical approach by utilizing a high-order backward differencing operator can make the process become stationary, and the commonly used method for assessing the frequency stability in the time domain is based on this idea. This paper focuses on the mathematical fundamentals behind the method for assessing the frequency stability of atomic clocks. The power-law noise is actually derived from the calculus of white noise processes and the different power-law noises correspond to the different stochastic differential equations. In fact, the simulation of the power-law noise is also achieved by some differentiations and integrations operating on the white noise process. This paper first introduces the identification method of different power-law noises and gives the differential equations corresponding to the power-law noises in conjunction with some available literatures. Then, the relationships between the different frequency stability assessment methods and their corresponding transfer functions are presented, and the calculation method of the confidence intervals is briefly summarized. This paper provides some insight into the construction of the stochastic model for atomic clocks and methods for assessing frequency stability in a relatively systematic basis.
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