基于转发式卫星导航定位系统的思路,以与导航定位精度有密切关系的星座的位置精度衰减因子(Position Dilution of Precision,PDOP)在中国区域的分布和变化为主要评判依据,分析讨论由静止通信卫星和倾斜轨道同步通信卫星组成转发式中国区域定位系统星座的初步计划.我们重点考虑倾斜轨道同步卫星的3个主要的轨道参数,即轨道倾角、偏心率及升交点赤经的变化对PDOP的影响,通过仿真计算研究了该区域导航定位系统优良星座的布局方案.对多种星座布局分析比较的初步结果表明,设置3颗位于一组使‘8’字形星下点共迹的倾斜轨道同步通信卫星,它们的轨道倾角约为50°,卫星升交点的赤经差为120°,且其星下点轨迹的对称中心处在115°E附近,与4颗或5颗分布于约60°E至165°E轨位处的静止通信卫星组成转发式中国区域卫星定位系统的星座,可以满足对中国陆地和海疆的有效覆盖,可获得相对高精度的导航定位结果.给出了3个相对优秀的星座结构的初步结果,并讨论了有关的问题.
The Chinese Area Positioning System （CAPS）, a navigation system based on geostafionary orbit （GEO） communication satellites, was developed in 2002 by astronomers at Chinese Academy of Sciences. Extensive positioning experiments of CAPS have been performed since 2005. On the basis of CAPS, this paper studies the principle of a navigation constellation composed of slightly inclined geostationary orbit （SIGSO） communication satellites. SIGSO satellites are derived from GEO satellites which are near the end of their operational life by inclined orbit operation. Considering the abundant frequency resources of SIGSO satellites, multi-frequency observations could be conducted to enhance the precision of pseudorange measurements and ameliorate the positioning performance. A constellation composed of two GEO satellites and four SIGSO satellites with an inclination of 5° can provide service to most of the territory of China with a maximum position dilution of precision （PDOP） over 24 h of less than 42. With synthetic utilization of the truncated precise code and a physical augmentation factor in four frequencies, the navigation system with this constellation is expected to obtain comparable positioning performance to that of the coarse acquisition code of the Global Positioning System （GPS）. When the new method of code-carrier phase combinations is adopted, the system has the potential to possess commensurate accuracy with the precise code in GPS. Additionally, the copious frequency resources can also be used to develop new anti-interference techniques and integrate navigation and communication.
