Optimal Weighted Subspace Fitting Direct Position Determination Method with HF/UHF Collaboration
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摘要: 针对超视距多目标的定位问题,本文提出了一种基于最优加权子空间拟合(OWSF)的短波超短波协同直接定位(DPD)方法。首先建立了超视距定位场景下短波超短波信号传播模型,短波模型是通过电离层反射的二维到达方向(DoA)模型,涵盖了方位角和俯仰角信息;超短波模型是基于运动阵列观测的空时信号扩展模型,包含一维到达角度和多普勒频率信息。与现有依赖单频段信号的定位方法不同,新方法将两种观测信号的信号子空间与噪声子空间加权融合,实现了两种定位频段信号的优势互补,从而显著提高了定位精度。此外,文中还推导了地球椭球约束条件下定位估计误差克拉美罗界(CRB)。仿真结果显示,新方法在高信噪比条件下能够逼近克拉美罗界,且相较于已有算法具有更强的空间分辨能力,在低信噪比条件下具有显著的定位精度优势。Abstract:
Objective Passive localization technology plays an indispensable role in target detection, navigation, and track tracking, particularly in military applications involving maritime and aerial targets. These targets often utilize complex communication systems covering multiple frequency bands, such as Shortwave (HF) and Ultra-Shortwave (UHF). Existing localization methods mainly rely on single-frequency bands or Two-Step positioning approaches. However, single-band methods fail to fully exploit the diverse position feature information contained in different signals, while Two-Step methods suffer from information loss during the intermediate parameter estimation process (e.g., DOA, TDOA), leading to reduced accuracy. Furthermore, current Direct Position Determination (DPD) research rarely addresses the collaborative fusion of HF signals (utilizing ionospheric reflection) and UHF signals (utilizing Doppler effects from moving arrays). To address the challenges of low positioning accuracy and poor spatial resolution in over-the-horizon multi-target scenarios, this study aims to propose a novel collaborative DPD method. This method is designed to integrate the complementary advantages of HF and UHF bands, thereby significantly enhancing localization precision and robustness in complex electromagnetic environments. Methods To achieve high-precision localization, this paper proposes an Optimal Weighted Subspace Fitting (OWSF) DPD method. First, comprehensive signal propagation models are established for the heterogeneous observation platforms ( Fig. 1 ). For HF signals, a two-dimensional Direction of Arrival (DOA) model is constructed based on ionospheric reflection, incorporating azimuth and elevation angle information to handle non-linear over-the-horizon propagation. For UHF signals, a space-time extended signal model is developed for a moving Unmanned Aerial Vehicle (UAV) platform. This model utilizes the station's motion to exploit the Doppler effect, effectively creating a virtual large-aperture array to capture both one-dimensional angle and Frequency of Arrival (FOA) information. Secondly, unlike traditional methods that process bands separately, the proposed OWSF algorithm constructs a unified cost function. This function fuses the signal subspaces and noise subspaces of both HF and UHF observed data using optimal weighting matrices to balance the contributions of different signal qualities. The target position is then estimated by minimizing this cost function via a grid search or Newton iteration method. Additionally, the theoretical performance limit is established by deriving the Cramér-Rao Bound (CRB) for the positioning estimation error under the geometric constraints of the Earth ellipsoid.Results and Discussions Numerical simulations were conducted in a centralized processing scenario where data is transmitted to a central station ( Fig. 2 ) to validate the effectiveness and performance of the proposed method. The simulation setup involved three stationary targets and a collaborative system comprising shortwave stations and a UAV (Fig. 3 ,Table 2 ,Table 3 ). Performance comparisons demonstrate that the proposed OWSF method consistently outperforms traditional Two-Step positioning methods and single-system DPD methods (DOA-only or FOA-only) in terms of Root Mean Square Error (RMSE) (Fig. 4 ). Specifically, under conditions where the Signal-to-Noise Ratio (SNR) of the HF signal is 5dB lower than that of the UHF signal, the OWSF algorithm exhibits superior robustness compared to existing algorithms such as the Subspace Data Fusion (SDF) and Minimum Variance Distortionless Response (MVDR) methods, closely approaching the theoretical CRB at high SNR levels (Fig. 5 ). The impact of system parameters was also analyzed, showing that increasing the number of sampling points (Fig. 6 ) and array elements (Fig. 7 ) improves accuracy, particularly in low SNR regimes. Furthermore, regarding spatial resolution, the OWSF algorithm generates sharper spectral peaks for distant targets and successfully resolves closely spaced targets that the conventional SDF-DPD algorithm fails to distinguish (Fig. 8 ,Fig. 9 ).Conclusions This paper presents a robust HF/UHF collaborative Direct Position Determination method based on Optimal Weighted Subspace Fitting. By mathematically modeling the ionospheric reflection for HF signals and the space-time Doppler characteristics for UHF signals, the method effectively fuses multi-dimensional observational information. Simulation results verify that the new method significantly improves positioning accuracy and spatial resolution compared to existing algorithms, particularly in scenarios with low SNR or unequal signal quality between bands. The derivation of the CRB provides a solid theoretical benchmark for the system. The proposed approach successfully overcomes the bottlenecks of single-band limitations and the information loss inherent in two-step methods, proving to be a highly effective solution for over-the-horizon passive localization of multiple stationary targets. -
算法:基于最优加权子空间拟合的直接定位算法 输入:短波观测站坐标$ \boldsymbol{\tilde{u}}_{}^{d} $,无人机坐标$ \boldsymbol{\tilde{u}}_{}^{f} $,短波信号采样数据$ \boldsymbol{x}_{}^{d} $,超短波信号采样数据$ \boldsymbol{x}_{}^{f} $。 输出:目标坐标估计结果$ {\widehat{\boldsymbol{u}}}_{{{n}_{r}}}\text{(}{n}_{r}=1,2,\cdots ,{N}_{r}\text{)} $ 1. $ {n}_{d}=1 $, $ {N}_{d} $ do 2. 计算协方差矩阵$ \mathbf{\hat{R}}_{{n}_{d}}^{d}=\dfrac{1}{N}\displaystyle\sum \nolimits_{n=1}^{N}\boldsymbol{x}_{{n}_{d}}^{d}\left(n\right)\boldsymbol{x}_{{n}_{d}}^{d\text{H}}\left(n\right) $ 3. 特征值分解,得到特征值$ [\lambda _{{n}_{d,}1}^{d},\lambda _{{n}_{d,}2}^{d},\cdots ,\lambda _{{n}_{d,}{M}_{d}}^{d}] $、信号子空间$ \mathbf{U}_{{n}_{d}}^{d,s} $和噪声子空间$ \mathbf{U}_{{n}_{d}}^{d,n} $ 4. end for 5. for $ {n}_{f}=1 $, $ {N}_{f} $ do 6. 建立扩展空时信号模型$ \boldsymbol{\tilde{x}}_{{n}_{f}}^{f} $ 7. 计算协方差矩阵$ \mathbf{\hat{\tilde{R}}}_{{n}_{f}}^{f}=\dfrac{1}{N}\displaystyle\sum \nolimits_{n=1}^{N}\boldsymbol{\tilde{x}}_{{n}_{f}}^{f}\left(n\right)\boldsymbol{\tilde{x}}_{{n}_{f}}^{f\text{H}}\left(n\right) $ 8. 特征值分解,得到特征值$ [\lambda _{{n}_{f},1}^{f},\lambda _{{n}_{f},2}^{f},\cdots ,\lambda _{{n}_{f},L{M}_{f}}^{f}] $、信号子空间$ \mathbf{U}_{{n}_{f}}^{f,s} $和噪声子空间$ \mathbf{U}_{{n}_{f}}^{f,n} $ 9. end for 10.for $ {n}_{r}=1, $ $ {N}_{r} $ do 11.根据公式(47)和(48)计算$ g\left(\boldsymbol{u}\right)={g}_{d}\left(\boldsymbol{u}\right)+{g}_{f}\left(\boldsymbol{u}\right) $ 12.搜索极小值得到估计结果$ {\widehat{\boldsymbol{u}}}_{{{n}_{r}}}=\underset{\boldsymbol{u}}{\arg \min }g\left(\boldsymbol{u}\right) $ end for 注释:由于$ g\left(\boldsymbol{u}\right) $在每个目标的定位范围内为凹函数,所以在定位过程中可以先通过DOA交汇定位法获得第$ q $个目标的初始估计$ \boldsymbol{\hat{u}}_{{n}_{r}}^{0} $,然后通过网格搜索或Newton迭代法对$ g\left(\boldsymbol{u}\right) $求$ {N}_{r} $次极小值,可以避免在对多目标定位时高维度优化带来的计算复杂度。 表 1 算法计算复杂度对比
算法 信号协方差矩阵估计 特征值分解 代价函数搜索 OWSF-DPD $ O\left(4M_{d}^{2}N{N}_{d}+4M_{f}^{2}{L}^{2}N{N}_{f}\right) $ $ O\left(M_{d}^{3}{N}_{d}+M_{f}^{3}L{N}_{f}\right) $ $ O\left(\left(\begin{array}{l}16N_{r}^{2}{M}_{d}{N}_{d}+2N_{r}^{}{M}_{d}{N}_{d}\\+8{M}_{d}{N}_{d}+{N}_{d}\\+16N_{r}^{2}{M}_{f}L{N}_{f}\\+2N_{r}^{}{M}_{f}L{N}_{f}\\+8{M}_{f}L{N}_{f}+{N}_{f}\end{array}\right){N}_{r}{N}_{p}\right) $ SDF-DPD $ O\left(4M_{d}^{2}N{N}_{d}+4M_{f}^{2}{L}^{2}N{N}_{f}\right) $ $ O\left(M_{d}^{3}{N}_{d}+M_{f}^{3}L{N}_{f}\right) $ $ O\left(\left(\begin{array}{l}2M_{d}^{2}{N}_{d}-2{M}_{d}{N}_{r}{N}_{d}\\+{M}_{d}{N}_{d}\\+2LM_{f}^{2}{N}_{f}-2L{M}_{f}{N}_{r}{N}_{f}\\+L{M}_{f}{N}_{f}\end{array}\right){N}_{r}{N}_{p}\right) $ 表 2 目标辐射源经纬度坐标
目标 目标-1 目标-2 目标-3 经度 $ 121.50{^{\circ}}\text{E} $ $ 114.30{^{\circ}}\text{E} $ $ 118.30{^{\circ}}\text{E} $ 纬度 $ 37.90{^{\circ}}\text{N} $ $ 38.20{^{\circ}}\text{N} $ $ 36.18{^{\circ}}\text{N} $ 表 3 短波观测站经纬度坐标及电离层虚高
短波观测站 短波-1 短波-2 短波-3 经度 $ 117.12{^{\circ}}\text{E} $ $ 118.45{^{\circ}}\text{E} $ $ 119.98{^{\circ}}\text{E} $ 纬度 $ 36.99{^{\circ}}\text{N} $ $ 34.98{^{\circ}}\text{N} $ $ 35.69{^{\circ}}\text{N} $ 电离层虚高 (km) 340 360 375 表 4 目标辐射源经纬度坐标
观测单元 目标-1 目标-2 目标-3 经度 121.5°E 114.30°E 121.10°E 纬度 37.90°N 38.20°N 35.69°N -
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