A crucial issue of low earth orbit (LEO) navigation augmentation satellite constellation is to obtain a satellite clock of high medium–long stability (i.e., averaging time of 10–10,000 s) using a disciplined oscillator to reduce satellite size, weight, power consumption and cost, instead of using a large, heavy and expensive space atomic clock. To resolve this difficulty, we propose a new global navigation satellite system (GNSS) clock discipline technique via a stand-alone GNSS receiver. Consequently, high medium–long stability can be attained with the disciplined receiver oscillator. Based on the Doppler measurements calculated from carrier phases, precise clock drifts of the receiver oscillator are derived. According to the motion state of the LEO GNSS receiver, a precise clock drift estimation model is chosen to have good adaptability to the receiver's high dynamic movement. Then, the receiver oscillator is properly tuned to its nominal frequency at each epoch without loss of lock. An automatic closed-loop frequency control system using a third-order frequency-locked loop filter is proposed to periodically compensate the instantaneous frequency offsets of the user clock with respect to its nominal frequency. A nonlinear frequency steering method is proposed to overcome the receiver lost lock problem during the oscillator discipline process. The correctness and effectiveness of the proposed clock tuning technique were numerically verified with MATLAB first. Then, the oscillator discipline performances were tested with a VCH-1008 passive hydrogen maser, a LEO GNSS receiver and a PicoTime clock stability analyzer. With static real GPS data of a static receiver as well as with hardware simulated data of a LEO receiver, both the medium-term and long-term frequency stabilities of the disciplined oscillator were confirmed. Finally, the proposed oscillator discipline technique was implemented in a self-developed LEO GNSS receiver. A high-quality voltage-controlled crystal oscillator mounted on an onboard LEO receiver was used for our test both in a static situation and in a LEO dynamic environment. The experiment results show that the overlapping Allan deviation of the disciplined GNSS oscillator could be less than 7E-12 over periods of 1 to 4,000 s in both the static situation and the LEO moving situation for a 1070 km orbit with 1 Hz epoch sampling rate at the testing stage.

中文翻译：

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时钟调整技术，用于纪律严明的中长期稳定型GNSS振荡器，为LEO用户提供精确的时钟漂移

低地球轨道（LEO）导航增强卫星星座的一个关键问题是，使用受约束的振荡器来降低卫星尺寸，重量和功耗，从而获得具有中等至中长期稳定性（即平均时间为10–10,000 s）的卫星时钟。和成本，而不是使用大型，沉重和昂贵的太空原子钟。为解决此难题，我们提出了一种通过独立的GNSS接收器的新的全球导航卫星系统（GNSS）时钟纪律技术。因此，使用纪律严明的接收器振荡器可以实现较高的中长期稳定性。基于从载波相位计算出的多普勒测量，可以得出接收器振荡器的精确时钟漂移。根据LEO GNSS接收器的运动状态，选择一个精确的时钟漂移估计模型以对接收器的高动态运动具有良好的适应性。然后，在每个周期将接收器振荡器适当地调谐到其标称频率，而不会丢失锁定。提出了一种使用三阶锁频滤波器的自动闭环频率控制系统，以周期性地补偿用户时钟相对于其标称频率的瞬时频率偏移。提出了一种非线性频率转向的方法，以克服振荡器训练过程中的接收器失锁问题。首先用MATLAB数值验证了所提出的时钟调谐技术的正确性和有效性。然后，使用VCH-1008无源氢maser对振荡器的纪律性能进行了测试，LEO GNSS接收器和PicoTime时钟稳定性分析仪。利用静态接收器的静态真实GPS数据以及LEO接收器的硬件仿真数据，可以确定训练有素的振荡器的中期和长期频率稳定性。最后，在自行开发的LEO GNSS接收机中实施了提出的振荡器规则技术。安装在车载LEO接收器上的高质量压控晶体振荡器在静态和LEO动态环境下均用于我们的测试。实验结果表明，在10Hz km轨道和1Hz历元采样速率下，静态和LEO运动情况下，经过训练的GNSS振荡器在1至4,000 s的周期内重叠的Allan偏差都可以小于7E-12。测试阶段。利用静态接收器的静态真实GPS数据以及LEO接收器的硬件仿真数据，可以确定训练有素的振荡器的中期和长期频率稳定性。最后，在自行开发的LEO GNSS接收机中实施了提出的振荡器规则技术。安装在车载LEO接收器上的高质量压控晶体振荡器在静态和LEO动态环境下均用于我们的测试。实验结果表明，在10Hz km轨道和1Hz历元采样速率下，静态和LEO运动情况下，经过训练的GNSS振荡器在1至4,000 s的周期内重叠的Allan偏差都可以小于7E-12。测试阶段。利用静态接收器的静态真实GPS数据以及LEO接收器的硬件仿真数据，可以确定训练有素的振荡器的中期和长期频率稳定性。最后，在自行开发的LEO GNSS接收机中实施了提出的振荡器规则技术。安装在车载LEO接收器上的高质量压控晶体振荡器在静态和LEO动态环境下均用于我们的测试。实验结果表明，在10Hz km轨道和1Hz历元采样速率下，静态和LEO运动情况下，经过训练的GNSS振荡器在1至4,000 s的周期内重叠的Allan偏差都可以小于7E-12。测试阶段。