北斗GEO卫星用户算法的改进方法研究*

针对北斗GEO用户算法需要进行5?倾角的坐标旋转处理这一过程，本文提出了采用经典广播星历参数用户算法直接解算北斗GEO卫星位置的改进方法，并同时给出了相应的基于第二类无奇点根数的广播星历拟合算法。该算法采用第二类无奇点轨道根数代替经典轨道根数，解决了由GEO轨道的小倾角特性引起的经典广播星历参数拟合过程中法化矩阵奇异的问题。从而避免了北斗GEO用户算法中坐标旋转处理过程，减少了GEO用户算法的计算步骤。经过仿真验证，本文提出的改进方法在卫星轨道拟合过程中与原算法精度相当；在卫星轨道外推过程中与原算法相比略有精度损失，但仍满足用户导航定位精度的需求。最后，采用实际北斗GEO星历解算的轨道数据验证了改进算法的有效性。

Research on an Improved Ephemeris Algorithm of BeiDou GEO Satellite for User

The orbital inclination of 5°coordinate rotation is required in the GEO ephemeris algorithm for user. Aim at this step, this paper presents an improved method that the BeiDou GEO satellite position is calculated directly by using the classical broadcast ephemeris algorithm for user, and meanwhile, gives the corresponding broadcast ephemeris fitting algorithm based on the second class of non-singularity orbit elements. In this method, the classical orbit elements are replaced by the second class of non-singular orbit elements, which solves the problem that coefficient matrix is non-positive in the process of the classical broadcast ephemeris fitting algorithm because of the small inclination angle. This avoids the orbital inclination of 5°coordinate rotation process, decreases the calculating steps time and enhances the GEO ephemeris algorithmic efficiency. The simulation results show that the accuracy of the improved method is as much as the original algorithm in the satellite orbit fitting process and is reduced slightly in the satellite orbit extrapolation process. But it can still meet the requirement of navigation and position for users. Finally, the validity of the improved algorithm is verified by using orbital data of the actual BeDou GEO broadcast ephemeris.