Abstract The main challenge in real-time precise point positioning (PPP) is that the data outages or large time lags in receiving precise orbit and clock corrections greatly degrade the continuity and real-time performance of PPP positioning. To solve this problem, instead of directly predicting orbit and clock corrections in previous researches, this paper presents an alternative approach of generating combined corrections including orbit error, satellite clock and receiver-related error with broadcast ephemeris. Using ambiguities and satellite fractional-cycle biases (FCBs) of previous epoch and the short-term predicted tropospheric delay through linear extrapolation model (LEM), combined corrections at current epoch are retrieved and weighted with multiple reference stations, and further broadcast to user for continuous enhanced positioning during outages of orbit and clock corrections. To validate the proposed method, two reference station network with different inter-station distance from National Geodetic Survey (NGS) network are used for experiments with six different time lags (i.e., 5s, 10s, 15s, 30s, 45s and 60s), and one set of data collected by unmanned aerial vehicle (UAV) is also used. The performance of LEM is investigated, and the troposphere prediction accuracy of low elevation (e.g., 10-20degrees) satellites has been improved by 44.1% to 79.0%. The average accuracy of combined corrections before and after LEM is used is improved by 12.5% to 77.3%. Without LEM, an accuracy of 2 to 3 centimeters can be maintained only in case of small time lags, while the accuracies with LEM are all better than 2cm in case of different time lags. The performance of simulated kinematic PPP at user end is assessed in terms of positioning accuracy and epoch fix rate. In case of different time lags, after LEM is used, the average accuracy in horizontal direction is better than 3cm, and the accuracy in up direction is better than 5cm. At the same time, the epoch fix rate has also increased to varying degrees. The results of the UAV data show that in real kinematic environment, the proposed method can still maintain a positioning accuracy of several centimeters in case of 20s time lag.

中文翻译：

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使用广播星历对实时轨道和时钟校正进行全面中断补偿，用于模糊度固定的精确点定位

摘要 实时精确单点定位（PPP）面临的主要挑战是接收精确轨道和时钟改正时的数据中断或大时滞，大大降低了PPP定位的连续性和实时性。为解决这一问题，本文不再直接预测以往研究中的轨道和时钟改正，而是提出了一种替代方法，利用广播星历生成包括轨道误差、卫星时钟和接收机相关误差的组合改正。使用前一纪元的模糊度和卫星部分周期偏差 (FCB) 以及通过线性外推模型 (LEM) 的短期预测对流层延迟，检索当前纪元的组合校正并使用多个参考站加权，并进一步向用户广播，以便在轨道中断和时钟校正期间持续增强定位。为了验证所提出的方法，使用与国家大地测量 (NGS) 网络具有不同站间距离的两个参考站网络进行六种不同时滞（即 5 秒、10 秒、15 秒、30 秒、45 秒和 60 秒）的实验，以及还使用了无人机 (UAV) 收集的一组数据。考察了LEM的性能，低仰角（如10-20度）卫星的对流层预测精度提高了44.1%～79.0%。使用LEM前后组合校正的平均精度提高了12.5%至77.3%。没有LEM，只有在小时间滞后的情况下才能保持2到3厘米的精度，而在不同时滞的情况下，LEM 的精度均优于 2cm。在用户端模拟运动学 PPP 的性能是根据定位精度和历元定位率来评估的。在不同时滞的情况下，使用LEM后，水平方向的平均精度优于3cm，向上方向的精度优于5cm。同时，epoch修复率也有不同程度的提高。无人机数据结果表明，在真实运动环境下，所提方法在20s时滞的情况下仍能保持几厘米的定位精度。水平方向平均精度优于3cm，向上方向精度优于5cm。同时，epoch修复率也有不同程度的提高。无人机数据结果表明，在真实运动环境下，所提方法在20s时滞的情况下仍能保持几厘米的定位精度。水平方向平均精度优于3cm，向上方向精度优于5cm。同时，epoch修复率也有不同程度的提高。无人机数据结果表明，在真实运动环境下，所提方法在20s时滞的情况下仍能保持几厘米的定位精度。