A precision-control method based on step-constraint for low earth orbit (LEO) satellite clock

A high-precision time-frequency system is essential for real-time centimeter-level positioning services provided by low Earth orbit (LEO) navigation satellites. Oven-controlled crystal oscillators (OCXOs) are widely adopted as clock references for LEO satellites owing to their size, power, and cost advantages. However, limited OCXO long-term stability leads to rapid clock bias accumulation, significantly degrading position accuracy. In this study, a precise OCXO frequency control method based on the step constraint is proposed to improve long-term stability. A quantization noise error model is established, and a frequency adjustment constraint is constructed specifically for real-time high-precision positioning services. The precise OCXO frequency compensation via a 48-bit direct digital synthesizer (DDS) is systematically achieved as required by rapid and precise position applications. Experimental validation is conducted on a high-resolution OCXO-based time-frequency system. The results indicate that the root mean square (RMS) clock bias is reduced to approximately 0.26 ns. Moreover, long-term frequency stability at an averaging interval of 10,000 s is significantly improved to 2 × 10 −14 , which represents an enhancement of four orders compared to the OCXO free-running state, while the slight degradation of short-term stability at intervals of 1s to 20s is limited to 27%. Thus, the proposed approach provides an efficient, low-cost and high-precision time-frequency reference solution suitable for LEO navigation constellations.