A Time-Frequency Synchronization for Ka-band Inter Satellite Link of the Navigation Satellite System

Satellite navigation systems provide global coverage, offering continuous worldwide navigation, positioning, and timing functions. These satellites are equipped with Ka-band inter-satellite links, which enable distance measurement and information transmission, thereby providing emergency tracking and control functions for overseas spacecraft. Due to these links being the only means of measurement and emergency communication when ground measurement and control stations are unable to reach, an increasing number of overseas spacecrafts are attempting to connect to these Ka-band inter-satellite link<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sup>. The extended users such as space stations, satellites, and other spacecraft, constrained by weight and power limitations, are unable to carry atomic clocks for high-precision time-frequency references, therefore they can't connect to Ka-band inter-satellite links using traditional time-frequency synchronization methods. This paper proposes a novel time-frequency synchronization method for non-atomic clock spacecraft with low time-frequency accuracy connecting to the Ka-band inter-satellite links of navigation satellites, which is proposed for the first time in China. After completing pointing calculations and one-way capture tracking with limited time slot, the extended users collect one-way ranging data between navigation satellites, construct a clock estimation model, calculate clock offset parameters, and compensate for time and frequency, which can increase the accuracy of time and frequency by 20 times. In the case of limited time slot resources for Ka-band inter-satellite links, this technology solves the problem of high-precision time-frequency synchronization between non atomic clock extended users and navigation satel-lites, and realizes the low-time-frequency accuracy extended users connecting to the navigation inter-satellite link for the first time in our country, greatly improving the availability of Ka-band inter-satellite links. The technology has been applied in orbit and the ranging accuracy has reached 0.5 meters, which is at the leading level in China. It also enables overseas satellites and spacecraft to connect to Ka-band inter-satellite links, providing emergency tracking and control functions for overseas spacecraft, improving survivability of spacecraft and achieving significant social and political benefits.