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摘要:
码载分歧(CCD)监测器是卫星导航地基增强系统(GBAS)引入的完好性监测器之一,用于监测码伪距与载波相位观测值之间的不一致性。双频平滑技术的引入改变了CCD监测器的检验统计量等参数,进而影响了监测性能。针对双频GBAS中存在的频间偏差(IFB),基于北斗双频观测数据,分析IFB不确定性对于双频码载分歧监测性能的影响。研究结果表明:在IFB不确定性的影响下,监测器的阈值增大了26.1%,导致其在发生CCD故障情况下的漏检率显著增大,最小可检测故障值增大了26.9%,监测器的灵敏度降低;最坏情况下系统完好性损失概率从低于10−14增大到接近10−8,同时机载端为满足漏检率性能安全要求所引入的延迟值更大,导致CCD监测器的故障响应变慢,双频GBAS的完好性受到影响。
Abstract:Code carrier divergence (CCD) monitor is one of the integrity monitors introduced by ground-based augmentation systems (GBAS), which is used to monitor the inconsistency between code pseudorange and carrier phase observations. Dual-frequency smoothing technology changes the test statistics and other parameters of CCD monitor, which affect the monitoring performance. Considering the inter-frequency bias (IFB) introduced in dual-frequency GBAS, the impact of IFB uncertainty on the dual-frequency CCD monitoring is analyzed based on the dual-frequency observation data of BDS B1I and B3I signals. The results show that under the influence of IFB uncertainty, the threshold of the monitor increases by 26.1%, resulting in a significant increase of the probability of missed detection (PMD) in the case of CCD fault. And the minimum detectable fault increases by 26.9%, which means a decrease in the sensitivity of the monitor. Meanwhile, the probability of the loss of integrity in the worst case increases from less than 10−14 to nearly 10−8, and the delay introduced by the airborne to meet the PMD requirement is larger, resulting in a slower response of CCD monitor and impacts the integrity of dual-frequency GBAS.
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表 1 监测阈值比较
Table 1. Comparison of monitoring threshold
仿真试验场景 原始标准差/
(10−4 m·s−1)包络标准差/
(10−4 m·s−1)阈值/
(10−4 m·s−1)包含IFB不确定性 6.22 10 58 扣除IFB不确定性 4.17 7.88 46 表 2 不同监测阈值对应的漏检率对比
Table 2. Comparison of PMD related to different monitoring thresholds
监测阈值/(m·s−1) ${\mathrm{P}\mathrm{M}\mathrm{D}}_{1} $ ${\mathrm{P}\mathrm{M}\mathrm{D}}_{2} $ 7×10−5 11.68 0.12 8×10−5 1.39 7.99×10−4 9×10−7 6.87 1.18×10−4 1×10−7 1.33 3.62×10−7 1.1×10−10 9.96 2.29×10−8 表 3 CCD故障误差分析的仿真条件
Table 3. Simulation conditions of CCD fault error analysis
参数 数值 CCD监测器滤波时间常数$ {\tau }_{\mathrm{m}} $/s 30 Hatch滤波的时间常数$ \tau $/s 100 CCD故障发生的时刻$ {t}_{\mathrm{f}} $/s 450 地面双频CCD监测器初始化时刻$ {t}_{\mathrm{g},0} $/s 0 机载双频CCD监测器初始化时刻$ {t}_{\mathrm{a},0} $/s 600 从机载滤波器初始化到将测量值
应用于定位解的时间延迟$ {t}_{\mathrm{d}\mathrm{e}\mathrm{l}\mathrm{a}\mathrm{y}} $/s0, 50 地面端延迟$ {\tau }_{\mathrm{G}} $/s 1.5 数据及完好性信息的更新率$ {f}_{\mathrm{C}} $/Hz 2 仿真时间$ t $/s [0∶0.5∶1800] 故障$ d $/( m·s−1) 0.001 表 4 为满足PMD要求在机载端引入的最小$ {\mathit{t}}_{\mathbf{d}\mathbf{e}\mathbf{l}\mathbf{a}\mathbf{y}} $值
Table 4. Minimum $ {\mathit{t}}_{\mathbf{d}\mathbf{e}\mathbf{l}\mathbf{a}\mathbf{y}} $ introduced in airborn to meet PMD requirements
故障模式 包含IFB不确定性/s 扣除IFB不确定性/s MC1 (MP1) 50 22 MC3 (MP3) 6 0 -
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