Yao Jian, Levine Judah, Weiss Marc
National Institute of Standards and Technology, Boulder, Colorado 80305 USA; University of Colorado, Boulder, Colorado 80305 USA.
National Institute of Standards and Technology, Boulder, Colorado 80305 USA.
J Res Natl Inst Stand Technol. 2015 Nov 17;120:280-92. doi: 10.6028/jres.120.017. eCollection 2015.
The wide application of Global Positioning System (GPS) carrier-phase (CP) time transfer is limited by the problem of boundary discontinuity (BD). The discontinuity has two categories. One is "day boundary discontinuity," which has been studied extensively and can be solved by multiple methods [1-8]. The other category of discontinuity, called "anomaly boundary discontinuity (anomaly-BD)," comes from a GPS data anomaly. The anomaly can be a data gap (i.e., missing data), a GPS measurement error (i.e., bad data), or a cycle slip. Initial study of the anomaly-BD shows that we can fix the discontinuity if the anomaly lasts no more than 20 min, using the polynomial curve-fitting strategy to repair the anomaly [9]. However, sometimes, the data anomaly lasts longer than 20 min. Thus, a better curve-fitting strategy is in need. Besides, a cycle slip, as another type of data anomaly, can occur and lead to an anomaly-BD. To solve these problems, this paper proposes a new strategy, i.e., the satellite-clock-aided curve fitting strategy with the function of cycle slip detection. Basically, this new strategy applies the satellite clock correction to the GPS data. After that, we do the polynomial curve fitting for the code and phase data, as before. Our study shows that the phase-data residual is only ~3 mm for all GPS satellites. The new strategy also detects and finds the number of cycle slips by searching the minimum curve-fitting residual. Extensive examples show that this new strategy enables us to repair up to a 40-min GPS data anomaly, regardless of whether the anomaly is due to a data gap, a cycle slip, or a combination of the two. We also find that interference of the GPS signal, known as "jamming", can possibly lead to a time-transfer error, and that this new strategy can compensate for jamming outages. Thus, the new strategy can eliminate the impact of jamming on time transfer. As a whole, we greatly improve the robustness of the GPS CP time transfer.
全球定位系统（GPS）载波相位（CP）时间传递的广泛应用受到边界不连续性（BD）问题的限制。这种不连续性有两类。一类是“日边界不连续性”，对此已进行了广泛研究，并且可以通过多种方法解决[1 - 8]。另一类不连续性称为“异常边界不连续性（异常 - BD）”，它源于GPS数据异常。该异常可以是数据间隙（即数据缺失）、GPS测量误差（即坏数据）或周跳。对异常 - BD的初步研究表明，如果异常持续时间不超过20分钟，我们可以使用多项式曲线拟合策略修复异常来解决不连续性问题[9]。然而，有时数据异常持续时间会超过20分钟。因此，需要一种更好的曲线拟合策略。此外，周跳作为另一种数据异常类型，可能会出现并导致异常 - BD。为了解决这些问题，本文提出了一种新策略，即具有周跳检测功能的卫星时钟辅助曲线拟合策略。基本上，这种新策略将卫星时钟校正应用于GPS数据。之后，我们像之前一样对码和相位数据进行多项式曲线拟合。我们的研究表明，对于所有GPS卫星，相位数据残差仅约为3毫米。新策略还通过搜索最小曲线拟合残差来检测并找出周跳的数量。大量实例表明，无论异常是由于数据间隙、周跳还是两者的组合，这种新策略都能修复长达40分钟的GPS数据异常。我们还发现，GPS信号干扰（即“干扰”）可能会导致时间传递误差，并且这种新策略可以补偿干扰中断。因此，新策略可以消除干扰对时间传递的影响。总体而言，我们大大提高了GPS CP时间传递的鲁棒性。
