Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China.
Sensors (Basel). 2012;12(6):7518-28. doi: 10.3390/s120607518. Epub 2012 Jun 4.
Precise Point Positioning (PPP) has been demonstrated as a simple and effective approach for user positioning. The key issue in PPP is how to shorten convergence time and improve positioning efficiency. Recent researches mainly focus on the ambiguity resolution by correcting residual phase errors at a single station. The success of this approach (referred to hereafter as NORM-PPP) is subject to how rapidly one can fix wide-lane and narrow-lane ambiguities to achieve the first ambiguity-fixed solution. The convergence time of NORM-PPP is receiver type dependent, and normally takes 15-20 min. Different from the general algorithm and theory by which the float ambiguities are estimated and the integer ambiguities are fixed, we concentrate on a differential PPP approach: the satellite- and epoch differenced (SDED) approach. In general, the SDED approach eliminates receiver clocks and ambiguity parameters and thus avoids the complicated residual phase modeling procedure. As a further development of the SDED approach, we use a regional augmentation network to derive tropospheric delay and remaining un-modeled errors at user sites. By adding these corrections and applying the Robust estimation, the weak mathematic properties due to the ED operation is much improved. Implementing this new approach, we need only two epochs of data to achieve PPP positioning converging to centimeter-positioning accuracy. Using seven days of GPS data at six CORS stations in Shanghai, we demonstrate the success rate, defined as the case when three directions converging to desired positioning accuracy of 10 cm, reaches 100% when the interval between the two epochs is longer than 15 min. Comparing the results of 15 min' interval to that of 10 min', it is observed that the position RMS improves from 2.47, 3.95, 5.78 cm to 2.21, 3.93, 4.90 cm in the North, East and Up directions, respectively. Combining the SDED coordinates at the starting point and the ED relative coordinates thereafter, we demonstrate the performance of RTK PPP with standard deviation of 0.80, 1.34, 0.97 cm in the North, East and Up directions.
精密单点定位（PPP）已被证明是一种简单有效的用户定位方法。PPP 的关键问题是如何缩短收敛时间，提高定位效率。最近的研究主要集中在通过在单个站纠正残余相位误差来解决模糊度的问题上。这种方法的成功（以下简称 NORM-PPP）取决于多快能够固定宽巷和窄巷模糊度，以实现第一个模糊度固定解。NORM-PPP 的收敛时间取决于接收机类型，通常需要 15-20 分钟。与通常用于估计浮点模糊度和固定整数模糊度的算法和理论不同，我们专注于差分 PPP 方法：卫星和历元差分（SDED）方法。一般来说，SDED 方法消除了接收机钟差和模糊度参数，从而避免了复杂的残余相位建模过程。作为 SDED 方法的进一步发展，我们使用区域增强网络在用户站点处推导出对流层延迟和剩余未建模误差。通过添加这些校正并应用稳健估计，由于 ED 操作而导致的弱数学特性得到了很大改善。实现这种新方法，我们只需要两个历元的数据就可以实现 PPP 定位收敛到厘米级定位精度。使用上海六个 CORS 站的七天 GPS 数据，我们演示了当两个历元之间的间隔大于 15 分钟时，成功率定义为三个方向收敛到期望定位精度 10cm 的情况达到 100%的情况。将 15 分钟间隔的结果与 10 分钟间隔的结果进行比较，观察到北、东、向上的位置 RMS 分别从 2.47、3.95、5.78cm 提高到 2.21、3.93、4.90cm。将起始点的 SDED 坐标与之后的 ED 相对坐标相结合，我们展示了 RTK PPP 的性能，在北、东、向上的标准偏差分别为 0.80、1.34、0.97cm。
