Cai Changsheng, Gong Yangzhao, Gao Yang, Kuang Cuilin
School of Geosciences and Info-Physics, Central South University, Changsha 410083, China.
School of Surveying and Urban Spatial Information, Beijing University of Civil Engineering and Architecture, Beijing 100044, China.
Sensors (Basel). 2017 Jun 6;17(6):1302. doi: 10.3390/s17061302.
The single-frequency precise point positioning (PPP) technique has attracted increasing attention due to its high accuracy and low cost. However, a very long convergence time, normally a few hours, is required in order to achieve a positioning accuracy level of a few centimeters. In this study, an approach is proposed to accelerate the single-frequency PPP convergence by combining quad-constellation global navigation satellite system (GNSS) and global ionospheric map (GIM) data. In this proposed approach, the GPS, GLONASS, BeiDou, and Galileo observations are directly used in an uncombined observation model and as a result the ionospheric and hardware delay (IHD) can be estimated together as a single unknown parameter. The IHD values acquired from the GIM product and the multi-GNSS differential code bias (DCB) product are then utilized as pseudo-observables of the IHD parameter in the observation model. A time varying weight scheme has also been proposed for the pseudo-observables to gradually decrease its contribution to the position solutions during the convergence period. To evaluate the proposed approach, datasets from twelve Multi-GNSS Experiment (MGEX) stations on seven consecutive days are processed and analyzed. The numerical results indicate that the single-frequency PPP with quad-constellation GNSS and GIM data are able to reduce the convergence time by 56%, 47%, 41% in the east, north, and up directions compared to the GPS-only single-frequency PPP.
单频精密单点定位（PPP）技术因其高精度和低成本而受到越来越多的关注。然而，为了达到几厘米的定位精度水平，通常需要很长的收敛时间，一般为几个小时。在本研究中，提出了一种通过结合四星系统全球导航卫星系统（GNSS）和全球电离层图（GIM）数据来加速单频PPP收敛的方法。在该方法中，GPS、GLONASS、北斗和伽利略观测数据直接用于非组合观测模型，从而可以将电离层和硬件延迟（IHD）作为一个单一未知参数一起估计。然后，将从GIM产品和多GNSS差分码偏差（DCB）产品中获取的IHD值用作观测模型中IHD参数的伪观测值。还针对伪观测值提出了一种时变权重方案，以便在收敛期间逐渐降低其对位置解的贡献。为了评估所提出的方法，对来自七个连续日的十二个多GNSS实验（MGEX）站的数据集进行了处理和分析。数值结果表明，与仅使用GPS的单频PPP相比，采用四星系统GNSS和GIM数据的单频PPP在东、北和天顶方向的收敛时间分别能够减少56%、47%和41%。
