两种状态下GPS时间比对的频谱特性分析

Analysis of Spectrum Characteristics of GPS Time Comparison Under Two Conditions

为了了解受ＳＡ（ＳｅｌｅｃｔｉｖｅＡｖａｉｌａｂｉｌｉｔｙ）效应影响的ＧＰＳ时间比对特性，１９９２年初进行了一些实验，实验的数据取样时间为１０秒，卫星跟踪时间为１小时。频谱分析的结果表明：１）正常状态下，ＧＰＳ时间比对的频谱特性是基本平坦的，没有明显的周期现象，噪声过程为调相白噪声；２）当ＧＰＳ时间比对受ＳＡ效应影响时，低频谱较明显，有明显的周期现象，其中５～１５分钟的周期信号约占７７％。这就是导致ＧＰＳ时间比对精度显著下降的原因。

At the beginning of 1992, some experiments were carried out in order to understand the characteristics of GPS time comparison affected by SA (Selective availability) effect. The sampling time of data is 10s and the tracking period of satellite is 1h in the experiments. The results of spectral analyses are shown as follows: 1)Under normal conditions, the spectrum characteristics of GPS time comparison are basically smooth, there are no obvious periodic phenomena and the noise process is white noise PM. 2) When GPS time comparison is affected by SA effect, the low spectra are relatively obvious, and there are obvious periodic phenomena. The periodic signals of 5～15 min take up about 77% among these obvious periods. That is the reason which leads to a marked drop in precision of GPS time comparison.