多类型历书对首次定位性能的影响研究
Two Sets of GPS Almanac on Time-to-first-fix Influence
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摘要: 研究了GPS接口文件中规定的高精度历书和中等精度历书两种不同格式历书对接收机捕获卫星信号的影响,比较两种历书与广播星历数据计算的卫星位置和速度之差,分析两种历书带来的码相位和多普勒频移搜索的不确定度,进而估计两种历书对于首次定位时间的影响。利用实际的历书数据在多城市进行一周时间的仿真分析。结果表明:历书数据龄期为一周时,高精度历书的精度无明显变化,能够较为有效地压缩码相位搜索空间,改善首次定位时间;而中等精度历书精度逐渐变差,其首次定位时间逐渐增大。Abstract: As almanac data effects the acquisition of satellites signals,two sets of almanac,high almanac and midi almanac were investigated.High almanac,mid almanac and GPS broadcast ephemeris data were compared in satellite position and velocity,code phase and Doppler frequency drift search space ambiguity and time-to-first-fix(TTFF).Simulation analysis was done in many cities with the actual almanac data.Results show that high almanac degrades little but mid almanac degrades in accuracy over the time span of one week.Over the first two d high almanac and mid almanac shall be very close in TTFF;over the subsequent five d,high almanac will be superior to midi almanac to second level in TTFF.
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