两种状态下GPS时间比对的时域特性分析

THE ANALYSIS OF TIME DOMAIN CHARACTERISTICS FOR GPS TIME COMPARISON UNDER TWO CONDITIONS

为了了解SA效应对GPS时间比对的影响，我们从1991年底到1992年初进行了一些实验，并对两种状态下的GPS时间比对的时域特性进行了比较。本文描述了得到的一些结果。1．方差分析表明：受SA效应影响的结果比正常状态的结果相差较大。（1）短期（取样时间为10秒，数据长度为13分钟）结果为时间比对精度降低了5～10倍，频率稳定度降低了约2倍多；（2）长期（取样时间为1天，数据长度为1个月）结果为时间比对精度降低了3～5倍，频率稳定度降低了4～15倍。2．短期的噪声特性分析表明：正常状态下GPS时间比对的噪声过程为调相白噪声，受SA效应影响GPS时间比对的噪声过程呈波浪性变化，主要是低频噪声。

From October 1991 to January 1992, we carried out some experiments in order to understand the influence of SA effects on GPS time comparison, and derived the time domain characteristics of GPS time comparison under two conditions.Some results have been described in this paper.1. The results of the variance analyses are shown that the results affected by SA effects haye been more different from those obtained under the normal condi-tions. (1) The results of the short term (the sampling time of data is 10 seconds and the data length is 13 minutes) have indicated that the precision of time com-parison is reduced by a factor of about 5~10 times, and the frequency stability is reduced by a faetor of about 2 times. (2)The results of the long term(the sampling time of data is 1 day and the data length is one month) have indicated that the precison of time comparison are reduced by a factor of about 3~5 times, and the frequency stability are reduced by a factor of about 4~15 times.2. The analysis results of noise characteristics in the short term have indica-ted that the noise process of GPS time comparison under the normal conditions is the white noise PM, and the noise process of GPS time comparison affected by SA presents wave change and it is mainly low frequency noise . The noise process appearing within the different sampling time are following: Sampling time Noise process (1) 10~40 seconds white FM (2) 50~100 seconds random walk FM (3) 150~500 seeonds flicker PM or white PM