A Closed-loop Feedback Adaptive Beam Alignment Algorithm for Shipborne LEO Satellite Communication Terminals
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摘要: 海上风浪扰动导致船舶与低轨(LEO)卫星间产生非线性相对运动,其复杂动态特性加剧了船载相控阵终端与星载相控阵终端间实现波束对准的技术难度,成为制约海洋低轨卫星通信稳定性与可靠性的关键瓶颈。针对船舶与低轨卫星构成的“动动通”通信场景,本文提出了一种闭环反馈式自适应对星算法:采用块稀疏贝叶斯学习(block-SBL)算法实现基于粗糙网格的快速目标捕获,再通过自适应牛顿迭代法提升离网估计精度;在此基础上,将离网估计结果输入无迹卡尔曼滤波器(UKF),预测并补偿船体在算法处理时延内新产生的姿态偏差,最终形成捕获与追踪协同的闭环反馈式自适应对星算法。基于真实海况下28,000-DWT级散货船实测运动姿态数据的仿真结果表明,在高海况条件下,相较于现有的离网波达方向(DOA)估计算法,所提算法不仅能有效校准估计结果,其计算复杂度亦显著降低。Abstract:
Objective The 6G-based satellite communication (SATCOM) network has emerged as the primary solution for achieving ubiquitous communication and oceanic communications. Compared with traditional geostationary earth orbit (GEO) satellites, the latest generation of low earth orbit (LEO) satellites offer higher throughput, lower end-to-end latency, and reduced deployment costs. Thus, phased arrays have been widely adopted in LEO SATCOM due to their beam agility. However, maritime wind-wave disturbances induce nonlinear relative motion between shipborne terminals and LEO satellites, posing severe challenges for high-precision satellite acquisition and tracking. To solve this problem, LEO SATCOM systems require a novel beam alignment algorithm that first obtains the target’s instantaneous state and motion characteristics through a target acquisition algorithm, then utilizes multi-target tracking method to predict satellite trajectories based on target states, compensating for estimation errors caused by severe coupled motions. Methods The proposed closed-loop feedback adaptive beam alignment algorithm consists of two tightly coupled components: target acquisition and target state updating. In the target acquisition stage, a rank reduction estimator (RARE) is first employed to decompose the array factor matrix and transform the original two-dimensional direction of arrival (DOA) estimation problem into two sequential one-dimensional estimations, which significantly reduces the computational complexity of each sparse Bayesian learning (SBL) iteration. Based on the coarse grid obtained from RARE, an adaptive Newton sparse Bayesian learning (ANSBL) method is developed. ANSBL utilizes block-sparse Bayesian learning to achieve initial target acquisition on the coarse grid and subsequently performs two-stage Newton refinement to mitigate off-grid mismatch, thereby providing high-accuracy DOA estimation in both $ \theta $ and $ \varphi $ and effectively improving angular observation precision. In the target state updating stage, an unscented Kalman filter (UKF)-based ternary joint prediction mechanism is introduced. The UKF simultaneously predicts the target’s motion state, the signal variance, and the noise variance for next target acquisition process. These predicted probability distributions are then used to update the initial grid and hyperparameters of the subsequent SBL acquisition stage, providing more consistent and comprehensive initial values. Through this closed-loop interaction, target acquisition and state tracking are deeply integrated, which substantially reduces the number of SBL iterations required for convergence. This improvement is particularly significant under high sea-state conditions where reducing beam alignment time is essential. Results and Discussions The proposed closed-loop feedback adaptive beam alignment algorithm first uses on-grid DOA estimation to reduce array factor correlation and improve efficiency during target acquisition, then utilizes Newton iteration for higher off-grid accuracy ( Fig. 3 ). Subsequently, the proposed method was validated using real-world ship attitude data collected from a 28,000-DWT bulk carrier under actual sea conditions (Fig. 4 ). The UKF refines DOA results via state updating, with its prediction of signal position, signal variance, and noise variance providing accurate hyperparameter initial values, thus reducing iterations and converging faster than other algorithms (Figs. 5 ). Under low sea-state conditions, the proposed method not only achieves satellite alignment in less than 0.2 seconds, but also reduces the satellite position estimation error from ±1° to ±0.5° (Fig. 6(a) ). Furthermore, under high sea-state conditions, the UKF effectively predicts satellite positions; more importantly, it cuts the satellite position estimation error from ±2.5° to ±0.65°, fully verifying the method’s robust tracking accuracy and error mitigation capability in harsh marine environments (Fig. 6(b) ).Conclusions To address the performance requirements of beam alignment algorithms for LEO communication satellites, this paper proposes a closed-loop feedback adaptive beam alignment algorithm. The algorithm first employs a block-based SBL algorithm to obtain grid-based DOA estimation results, and achieves super-resolution direction estimation under off-grid conditions via adaptive Newton iteration. Through the UKF, the estimation results are dynamically calibrated in real time. The UKF further predicts the target’s motion state, the signal variance, and the noise variance for the next target acquisition process, thereby enhancing tracking continuity and alignment accuracy. Numerical simulations demonstrate that the proposed algorithm outperforms traditional beam alignment methods in both numerical accuracy and robustness, effectively mitigating severe shaking interference from terminals under complex sea conditions. -
表 1 SU-ANSBL流程表
SU-ANSBL 1.初始化: 迭代参数:追踪时刻$ t=0 $;追踪总次数:$ {T}_{\text{track}} $;追踪间隔$ {\Delta }_{t} $ 实施ANSBL,获得初始状态矩阵:$ {\boldsymbol{E}}_{p,0} $、$ {\boldsymbol{E}}_{\boldsymbol{\delta },0} $、$ {\boldsymbol{E}}_{\sigma ,0} $和初始方差矩阵:$ {\boldsymbol{P}}_{p,0} $、$ {\boldsymbol{P}}_{\boldsymbol{\delta },0} $、$ {\boldsymbol{P}}_{\sigma ,0} $ 2. SU-ANSBL: 当$ t\leq {T}_{\text{track}} $时: 更新各均值矩阵和方差矩阵的先验预测值:$ {{\overline{\boldsymbol{\chi }}}}_{p,t|t-1} $、$ {{\overline{\boldsymbol{\chi }}}}_{\boldsymbol{\delta },t|t-1} $、$ {{\overline{\boldsymbol{\chi }}}}_{\sigma ,t|t-1} $、$ {\boldsymbol{P}}_{p,t|t-1} $、$ {\boldsymbol{P}}_{\boldsymbol{\delta },t|t-1} $、$ {\boldsymbol{P}}_{\sigma ,t|t-1} $ 更新字典矩阵$ {\boldsymbol{\boldsymbol{\varPhi }}}_{x} $和$ {{\boldsymbol{\varPhi }}}_{y} $,信号方差向量$ {\boldsymbol{\delta }}_{x} $和$ {\boldsymbol{\delta }}_{y} $,噪声方差$ {\sigma }^{2} $ 实施ANSBL,获得DOA估计结果,计算观测矩阵:$ {{\tilde{\boldsymbol{Z}}}}_{p,\text{t}} $、$ {{\tilde{\boldsymbol{Z}}}}_{\boldsymbol{\delta },0} $、$ {{\tilde{\boldsymbol{Z}}}}_{\sigma ,0} $ 更新各均值矩阵和方差矩阵的后验预测值:$ {{\overline{\boldsymbol{\chi }}}}_{p,t} $、$ {{\overline{\boldsymbol{\chi }}}}_{\boldsymbol{\delta },t} $、$ {{\overline{\boldsymbol{\chi }}}}_{\sigma ,t} $、$ {\boldsymbol{P}}_{p,t} $、$ {\boldsymbol{P}}_{\boldsymbol{\delta },t} $、$ {\boldsymbol{P}}_{\sigma ,t} $ 根据$ {{\overline{\boldsymbol{\chi }}}}_{p,t} $计算信号源位置的最终估计值并输出:$ \left({\tilde{\theta }}_{k},{\tilde{\varphi }}_{k}\right) $ $ t\leftarrow t+{\Delta }_{t} $ 表 2 28,000-DWT 级散货船,Walker星座参数表
名称 基本参数 数值 28,000-DWT 级散货船 垂直间长 160.4 m 船宽 27.2 m 平均吃水 8.16 m 常用航速 12节 Walker星座 $ N/P/F $ 160/8/0 卫星高度 1200 km轨道倾角 $ {60}^{\circ } $ -
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