Yao Jian, Levine Judah
National Institute of Standards and Technology, Boulder, Colorado 80305, USA.
JILA, University of Colorado, Boulder, Colorado 80309, USA.
J Res Natl Inst Stand Technol. 2016 Aug 8;121:372-388. doi: 10.6028/jres.121.017. eCollection 2016.
To do a better time comparison between high-precision clocks (such as a Cesium-fountain clock and Hydrogen-maser clock), we want to study and eventually lower the GPS carrier-phase time transfer noise. The GPS carrier-phase time transfer noise comes from four sources: GPS satellite, GPS signal path, ground receiving equipment (receiver and antenna), and data-processing algorithm. This paper focuses on the noise introduced by the ground receiving equipment. At NIST, we have installed seven GPS receivers. All receivers have the same reference time, i.e., UTC(NIST). Three of them are connected to the same antenna. The other four are connected to four different antennas. This architecture enables us to study the time-transfer noise from the ground receiving equipment. We study both long-term (> 100 days) noise and short-term (< 1 day) noise. For the long-term noise, the time-transfer result using one receiver can vary from that using another receiver by up to 1.8 ns, during 1.3 years. To achieve sub-nanosecond GPS timing accuracy, a careful monitoring of the time delays or a more frequent calibration is needed. For the short-term noise, we find that the common-clock difference between receivers using the same antenna is less noisy than that using two different antennas, at an averaging time of less than 0.5 hour. This indicates that the antenna and antenna cable contribute to the super-short-term noise of GPS carrier-phase time transfer significantly. In addition, the response to the GPS receiver's reference-time change is tested in this paper. The variation in the response can be up to ± 350 ps. Last, this paper gives the best carrier-phase time transfer result we can currently achieve with the available equipment at NIST. The best frequency stability is 4.0×10 at 3 hours, 1.1×10 at 1 day, 4.0×10 at 10 days, and 1.3×10 at 48 days.
为了在高精度时钟（如铯喷泉钟和氢脉泽钟）之间进行更好的时间比较，我们希望研究并最终降低GPS载波相位时间传递噪声。GPS载波相位时间传递噪声来自四个来源：GPS卫星、GPS信号路径、地面接收设备（接收器和天线）以及数据处理算法。本文重点关注地面接收设备引入的噪声。在美国国家标准与技术研究院（NIST），我们安装了七个GPS接收器。所有接收器都具有相同的参考时间，即协调世界时（NIST）。其中三个连接到同一个天线。另外四个连接到四个不同的天线。这种架构使我们能够研究地面接收设备的时间传递噪声。我们研究了长期（>100天）噪声和短期（<1天）噪声。对于长期噪声，在1.3年期间，使用一个接收器的时间传递结果与使用另一个接收器的结果相比，最多可相差1.8纳秒。为了实现亚纳秒级的GPS定时精度，需要仔细监测时间延迟或更频繁地进行校准。对于短期噪声，我们发现，在平均时间小于0.5小时的情况下，使用同一天线的接收器之间的共时钟差比使用两个不同天线的情况噪声更小。这表明天线和天线电缆对GPS载波相位时间传递的超短期噪声有显著贡献。此外，本文还测试了对GPS接收器参考时间变化的响应。响应变化可达±350皮秒。最后，本文给出了我们目前使用NIST现有设备所能获得的最佳载波相位时间传递结果。最佳频率稳定性在3小时时为4.0×10，在1天时为1.1×10，在10天时为4.0×10，在48天时为1.3×10。
