中国区域定位系统的水平定位误差分布研究

中国区域定位系统（Chinese Area Positioning System，CAPS）是基于通信卫星的转发式卫星导航系统，基本原理是导航信号由地面导航站上行，经通信卫星转发向地面广播，用户接收机接收导航信号和电文实现导航定位。在试验验证阶段，CAPS仅采用同步轨道通信卫星进行信号的转发和广播，用户接收机利用气压测高技术实现高程辅助下的定位解算。为了描述CAPS水平定位误差的分布，作者定义了高程辅助算法下的东精度衰减因子（Dilution of PrecisionEast，EDOP）和北精度衰减因子（Dilution of Precision North，NDOP）。根据CAPS星座分布，分析系统覆盖范围内高程辅助下EDOP和NDOP数值，结果表明CAPS的EDOP和NDOP是关于赤道南北对称，关于同步轨道通信卫星的平均经度子午圈对称。在平均经度子午圈附近，EDOP出现最小值；在同一纬度圈上，离平均子午圈越远，EDOP数值越大。在CAPS覆盖区域内，任一格点上的NDOP总是大于EDOP，当用户由低纬度地区向高纬度地区移动时，在站心坐标系内卫星在南北方向拉开的距离增大，NDOP变小。利用北京、上海、长春、西安、乌鲁木齐和昆明6个CAPS测站进行仿真分析，结果表明本文提出的EDOP和NDOP可用于估算星座空间布局对用户伪距测量误差的放大程度，并可以解释CAPS接收机在高程辅助下水平定位精度东西方向总是优于南北方向的现象。进一步的实测数据分析表明，EDOP和NDOP可以用来估算南北方向和东西方向的定位精度。

Analysis of Horizontal Positioning Error Distribution of the Chinese Area Positioning System

The Chinese Area Positioning System （CAPS） is a satellite-based system that transfers ground- generated navigation information to receivers via transmission of commercial geostationary communication satellites. During the test stage, CAPS only provides positioning signals from geostationary satellites and a receiver needs an incorporated barometric altimeter for altitude information to aid positioning. In order to describe the distribution of CAPS horizontal positioning errors, we define EDOP （ Dilution of Precision East） and NDOP （Dilution of Precision North ） of the altitude-aided algorithm. According to the calculations of EDOP and NDOP based on the CAPS constellation, the EDOP and NDOP values of CAPS are symmetric about the Equator, and are symmetric about the mean orbital longitude of the three geostationary satellites. The minimum of EDOP is reached around the meridian of the mean orbital longitude and the EDOP value increases as the receiver moves farther away from the mean. The NDOP is larger than the EDOP at any point in the CAPS coverage area. As the receiver moves from lower latitudes to higher latitudes, the north-south distances Kunming） and the constellation in the test stage. The results show that the EDOP and NDOP can be used to estimate the enlargement of User Equivalent Range Error （UERE） caused by the constellation, and explain the reason why the east-west precision is better than the north-south precision in CAPS positioning. The analysis of observed data from the six observation stations further shows that the EDOP and NDOP can be used to estimate the positioning precisions in the east-west and north-south directions.