GLONASS星历电文特征及其解算方法

针对飞行试验中由于GLONASS星历解算错误导致的定位结果异常问题,研究了GLONASS星历电文下传的基本特征,即通过第1~4串电文下传,并且一个更新周期内下传60组数据完全相同的星历。基于此,提出了基于电文串标识的GLONASS星历解算基本算法,但发现该算法在电文串丢失且发生星历更新时解算出错误星历的问题。为确保星历来源于连续的1~4串电文,提出了基于时间比较的星历解算改进算法,发现GLONASS星历更新时,不保证从第1串开始,也不保证在连续的1~4串电文中更新完毕,改进算法依然无法确保获取到正确星历。最后分析了星历电文误码时的特征,提出了基于星历合法性检测的星历解算可靠算法,该算法综合考虑卫星不健康、星历更新以及电文误码等异常情况,采用轨道特性检测法和原码比对检测法验证星历合法性,采用电文串标识法充分利用有效电文数据。试验结果表明,该算法的星历误码识别率达到100%,星历更新异常识别率达到100%,获取的GLONASS星历数据正确率到100%。

Characteristics and calculation method of GLONASS ephemeris’s message

To solve the problem of abnormal GLONASS positioning results due to falsely calculating ephemeris in flight task, the basic characteristics of GLONASS ephemeris’s message is described, which is transmitted from string 1~4 each frame, and sixty groups of ephemeris with the same data are transmitted within a update cycle. Then a basic algorithm is proposed to calculate GLONASS ephemeris basing on marked strings. It is found that the calculation will get fault ephemeris when there are lose strings during ephemeris is updating. In order to ensure ephemeris message is from one continue strings 1~4, an advanced algorithm is proposed based on received time comparing. But it is found that GLONASS ephemeris updates neither guarantee starting at string 1 nor end within one continue strings 1~4, so the advanced algorithm do not ensures getting right ephemeris. So the characteristics of message bit-error with ephemeris are analyzed, and a trusty algorithm is proposed to calculate GLONASS ephemeris based on ephemeris validity detection. In the trusty algorithm,the exceptional situations are all considered when ephemeris is malfunctioning, updating or the message has bit-errors. The validity of ephemeris is validated by the method of orbit property checking and the comparison of message bits. The valid message is full utilized by the marked strings. The trial results with the algorithm show that its recognition rate of bit-errors with ephemeris is 100%, its recognition rate of exceptional updated ephemeris is 100%, its correction rate of ephemeris is 100%.