He Kaifei, Weng Duojie, Ji Shengyue, Wang Zhenjie, Chen Wu, Lu Yangwei, Nie Zhixi
College of Oceanography and Space Informatics, China University of Petroleum (East China), Qingdao 266580, China.
Shenzhen Research Institute, The Hong Kong Polytechnic University, Shenzhen 518063, China.
Sensors (Basel). 2021 Jan 4;21(1):292. doi: 10.3390/s21010292.
Global navigation satellite systems (GNSS) can attain centimeter level positioning accuracy, which is conventionally provided by real-time precise point positioning (PPP) and real-time kinematic (RTK) techniques. Corrections from the data center or the reference stations are required in these techniques to reduce various GNSS errors. The time-relative positioning approach differs from the traditional PPP and RTK in the sense that it does not require external real-time corrections. It computes the differences in positions of a single receiver at different epochs using phase observations. As the code observations are not used in this approach, its performance is not affected by the noise and multipath of code observations. High reliability is another advantage of time-relative precise positioning because the ambiguity resolution is not needed in this approach. Since the data link is not required in the method, this approach has been widely used in remote areas where wireless data link is not available. The main limitation of time-relative positioning is that its accuracy degrades over time between epochs because of the temporal variation of various errors. The application of the approach is usually limited to be within a time interval of less than 20 min. The purpose of this study was to increase the time interval of time-relative positioning and to extend the use of this method to applications with a longer time requirement, especially in remote areas without wireless communication. In this paper, the main error sources of the time-relative method are first analyzed in detail, and then the approach to improve the accumulated time relative positioning method is proposed. The performance of the proposed method is assessed using both static and dynamic observations with a duration as long as several hours. The experiments presented in this paper show that, among the four scenarios tested (i.e., GPS, GPS/Galileo, GPS/Galileo/BeiDou, and GPS/Galileo/BeiDou/GLONASS), GPS/Galileo/BeiDou performed best and GPS/Galileo/BeiDou/GLONASS performed worst. The maximum positioning errors were mostly within 0.5 m in the horizontal direction, even after three hours with GPS/Galileo/BeiDou. It is expected that the method could be used for positioning and navigation for as long as several hours with decimeter level horizontal accuracy in remote areas without wireless communication.
全球导航卫星系统（GNSS）能够实现厘米级的定位精度，这通常是由实时精密单点定位（PPP）和实时动态（RTK）技术提供的。在这些技术中，需要来自数据中心或参考站的校正来减少各种GNSS误差。时间相对定位方法与传统的PPP和RTK不同，因为它不需要外部实时校正。它使用相位观测来计算单个接收机在不同历元的位置差异。由于该方法不使用码观测，其性能不受码观测噪声和多径的影响。高可靠性是时间相对精密定位的另一个优点，因为该方法不需要模糊度解算。由于该方法不需要数据链路，因此已在无线数据链路不可用的偏远地区广泛使用。时间相对定位的主要限制是，由于各种误差的时间变化，其精度在历元之间会随时间下降。该方法的应用通常限于小于20分钟的时间间隔内。本研究的目的是增加时间相对定位的时间间隔，并将该方法的使用扩展到具有更长时间要求的应用中，特别是在没有无线通信的偏远地区。本文首先详细分析了时间相对方法的主要误差源，然后提出了改进累积时间相对定位方法的途径。使用长达数小时的静态和动态观测来评估所提方法的性能。本文给出的实验表明，在测试的四种场景（即GPS、GPS/伽利略、GPS/伽利略/北斗和GPS/伽利略/北斗/格洛纳斯）中，GPS/伽利略/北斗表现最佳，GPS/伽利略/北斗/格洛纳斯表现最差。即使在使用GPS/伽利略/北斗三小时后，水平方向的最大定位误差大多在0.5米以内。预计该方法可用于在没有无线通信的偏远地区进行长达数小时的定位和导航，水平精度为分米级。
