A Novel Ground Verification System Based on Co-Frequency Link for Microwave Two-Way Time-Difference Measurements

High precision satellite-ground time-difference measurement is of great significance for improving the performance of Global Navigation Satellite Systems and promoting (GNSS) wide area network time synchronization. The current satellite-ground microwave link usually uses dual-frequency or triple-frequency links for two-way measurement, which helps to eliminate atmospheric errors to a certain extent. However, due to the limit of error elimination capabilities, the accuracy of time comparison can only reach the level of tens of ps. This study designs a time-frequency transfer system for uplink and downlink signals with the same frequency, ensuring the symmetry of the propagation paths of uplink and downlink signals. It is expected to be used to eliminate the influence of the satellite-ground space environment and the impact of complex and variable atmospheric environments. Interference cancellation has been achieved from three aspects: antenna isolation, radio frequency cancellation, and baseband cancellation in this study. This paper presents the verification by jointly evaluating equipment-level error measurements and spatial error simulation results. A ground verification system is built to evaluate the measurement jitter of equipment after Co-Channel Interference Cancellation (CCIC). The experimental results demonstrate that the degradation of the C/N0 of the received signal after CCIC is within the range of 3~4 dB compared to no-CCIC link, which can be compensated through link budget. The measurement jitter of the equipment after CCIC is better than 0.5 ps. The equipment delays stability after CCIC is better than 5e-17 at 10,000 s. Based on our previous spatial error simulation, the residual error of satellite-ground space correction can be better than 1.5 ps under the co-frequency link. The full link measurement jitter of the time-frequency transfer system based on co-frequency link between satellite and ground is expected to be less than 2 ps.