Wide-Area Multilateration Time Synchronization Method Based on Signal Arrival Time Modeling
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摘要: 针对低空监视技术广域多点定位(WAM)时间同步困难或复杂度高,影响定位精度的问题,该文构建了基于到达时间(TOA)的时间同步及“同一消息”提取的数学模型,通过计算地面传感器的“同步启动时间”完成同步,计算复杂度低且易于实现。在此基础上,利用同一消息提取模型筛选出TOA用于定位计算。为了提高TOA估计值的精度,减小同步误差。提出了可变滑动滤波与卡尔曼滤波结合 (VMAF-Kalman)的联合滤波方法,提高可编程门阵列 (FPGA)基准时钟的稳定性,减小时钟延迟引起的TOA计数误差。仿真结果表明,联合滤波比单一滤波算法效果更好,TOA计数误差分别降低36.84%和25.36%。对无人机和民航飞机的定位测验结果都表现出较高的定位准确率,定位误差和位置更新速率符合标准要求,证明该文所提模型,具有实用性且有较好的同步精度。Abstract:
Objective Wide-Area Multilateration (WAM), a high-precision positioning technology currently under nationwide deployment, is widely applied in aircraft positioning on airport surfaces and in terminal areas. However, as WAM depends on collaborative signal processing across multiple stations, challenges such as time synchronization and computational complexity continue to constrain positioning accuracy. This study develops a mathematical model for time synchronization and “same-message” extraction based on Time Of Arrival (TOA), achieving synchronization by calculating the “synchronized start time” of ground sensors. The proposed method offers low computational complexity and is straightforward to implement. To enhance TOA estimation accuracy and reduce synchronization error, a joint filtering strategy—Variable Moving Average Filtering and Kalman (VMAF-Kalman)—is proposed to minimize TOA counting deviations introduced by clock drift. The model addresses synchronization challenges in distributed station deployments and employs joint filtering to correct initial clock source deviations. Methods This study addresses the challenge of high-precision TOA acquisition by proposing a joint filtering method that combines VMAF-Kalman. This approach filters the phase difference count between the GPS 1 Pulse Per Second (1PPS) signal and the local crystal oscillator 1PPS signal, producing a stable reference clock to mitigate the effects of noise and oscillator aging that induce clock drift. Therefore, stable TOA counting with a precision of 2.5 ns is achieved in Field-Programmable Gate Arrays (FPGAs). To resolve synchronization issues in distributed WAM systems, a time synchronization model based on TOA is proposed, which determines the synchronized start time of remote stations. Additionally, a same-message extraction model is developed to identify the TOA of identical messages, enabling accurate multilateration positioning. Results and Discussions Two experiments evaluate the proposed method and model: a filtering performance comparison and an actual flight trajectory positioning experiment for time synchronization validation. The latter includes two simulation scenarios: Scenario 1 consists of drone positioning tests, and Scenario 2 consists of civil aviation aircraft positioning tests. The simulation results indicate that the joint filtering method outperforms single filtering approaches, reducing TOA counting errors by 36.84% and 25.36% in the respective scenarios. Both the drone and civil aviation tests demonstrate high positioning accuracy, with errors and update rates meeting standard requirements. These findings confirm the practicality of the proposed method and the improved synchronization accuracy of the model. Conclusions Firstly, the proposed VMAF-Kalman joint filtering method demonstrates clear advantages over single filtering algorithms in both performance and hardware efficiency. Simulation results show that the output of the PID controller remains within a narrower fluctuation range, while TOA counting errors are reduced by 36.84% and 25.36%, respectively. These findings confirm that joint filtering stabilizes clock signals, improves TOA counting accuracy in FPGAs, and reduces synchronization errors. Secondly, the time synchronization and same-message extraction models developed in this study simplify existing synchronization methods by enabling WAM synchronization and TOA extraction through algorithmic computation alone. Simulations incorporating actual flight data in low-altitude airspace, verified across multiple positioning algorithms, further validate the model. Drone test results show that vertical Root Mean Square Error (RMSE) and deviation remain within 20 m, with horizontal RMSE below 10 m. For civil aviation aircraft, all algorithms achieved accuracy rates above 80%, with average errors under 300 m and position update intervals within 5 s, meeting established standards. The experimental outcomes confirm the feasibility and applicability of the proposed model for high-precision WAM time synchronization. -
表 1 MAF和VMAF滤波结果
N=8 N=16 N=32 MAF-SD/s (s) 4.977 6×10–11 4.763 2×10–11 4.658 2×10–11 VMAF-SD/s (s) 4.794 5×10–11 4.706 2×10–11 4.646 1×10–11 MAF-OF 9.726 5×10–4 1.017 7×10–3 1.040 7×10–3 VMAF-OF 9.704 4×10–4 9.836 2×10–4 1.031 5×10–3 表 2 不同滤波算法的TOA计数差值
滤波方法 TOA计数平均差值
(时钟周期)(个)TOA计数平均差值
(时间)(ns)联合滤波 1.56 3.902 Kalman滤波 2.47 6.175 VMAF 2.09 5.225 表 3 不同定位算法定位结果
Chan算法 Chan-Taylor组合算法 Fang算法 $ {\bar s_{\mathrm{h}}} $(m) 136.630 8 101.571 8 120.481 2 $ {\bar s_{\mathrm{v}}} $(m) 174.502 6 131.751 7 160.341 8 $ \eta $(%) 80.44 87.02 82.58 $ t $(s) 3.42 4.18 3.73 -
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