| Cutting-edge technologies such as gravitational wave detection,verification of relativistic effects,and spacecraft interacting and docking put forward application requirements for high-precision time-frequency reference that have frequency stability better than E-16/day.The frequency stability of the atomic clock is better than the time-frequency reference signal of E-18/day,and the time-frequency signal needs to be transmitted to users through optical fiber,satellite,and other transmission methods.Time-frequency transfer using satellites has become the main methodology due to its advantages such as wide coverage and continuous availability.However,the current frequency stability of satellite-based time-frequency transfer is up to E-15/day,which cannot meet the application requirements of cutting-edge technology fields and cannot fully utilize the highly stable frequency resources of atomic clocks.In response to this problem,the paper relies on the relaying satellite navigation test system built by the National Time Service Center to investigate the high-precision carrier time-frequency transfer based on GEO communication satellites and realizes the frequency stability of E-16/day,which meets the application requirements such as gravitational wave detection.The main research results and innovations of the thesis are as follows:(1)A carrier phase time-frequency transfer method using communication satellite is put forward,and a time-frequency transfer model based on this method in one-way and two-way working modes is introduced.After the signal propagation process,the frequency and delay errors that are used in the two working modes are deeply analyzed,it is shown the main reason that affects the carrier frequency performance of the time-frequency propagation mainly lies in the retransmission of the satellite transponder.The magnitudes of the various error sources and the corresponding correcting methods that have influences on time delay are also investigated.(2)A method for measuring the local oscillator frequency of the communication satellite transponder is proposed and its performance is analyzed to assess the influence of the signal forwarding of the communication satellite on the carrier frequency of the time-frequency transfer.The result shows that the accuracy of the local oscillator frequency of the communication satellite transponder is inferior.In the order of E-8,and the frequency has a sine-like trend,some satellites also have rapid frequency modulation.These factors degrade the performance of time-frequency transfer of the carrier signal,leading to the impossibility to directly apply carrier phase observations in the system.(3)Given the influence of GEO communication satellite forwarding on the carrier time-frequency transfer,a local oscillator frequency measuring method based on a single-site closed-loop GEO communication satellite transponder is proposed and is analyzed.The results show that the local oscillator frequency of the GEO communication satellite transponder has a sine-like variation trend,and its accuracy is on the order of E-8,and the long-term stability is on the order of E-8 per ten thousand seconds.Some GEO communication satellites also have the phenomenon of fast frequency modulation,leading to the deterioration of the received signal and the impossibility to directly use the carrier phase observation.(4)Based on the relaying satellite navigation test system,a zero-baseline time-frequency transfer test was carried out in two working modes of GEO communication satellites:one way and two way.The C-band operating frequency was used to verify the carrier time and frequency transfer performance.The actual measurement results show that the time transfer accuracy obtained by using the carrier phase is an order of magnitude higher than the pseudo-code;the frequency stability of one-way carrier phase time-frequency transfer is at the level of 2.07×10-14/10000s;the frequency stability of two-way carrier phase time-frequency transfer is at the level of 1.29×10-14/1000s,1.21×10-15/10000s and 8.07×10-16/20000s. |
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