Robust Adaptive Beamforming for Sparse Arrays
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摘要: 波束形成技术在阵列信号处理,尤其是在波达方向估计方面发挥着关键作用。尽管传统的鲁棒波束形成方法能够处理导向矢量失配的问题,但它们未能充分利用阵列稀疏化带来的硬件优势,并且在存在干扰源时,难以有效抑制副瓣。因此,该文提出了一种能够协同优化鲁棒性、波束性能、副瓣电平与阵列稀疏性的统一框架。该文通过将l0范数作为稀疏约束、引入导向矢量误差以增强鲁棒性,并联合副瓣抑制约束,构建了一个全面的凸优化问题。特别地,该文在建模时进一步考虑了实际天线间的互耦效应,通过引入包含互耦参数的精确导向矢量模型,显著提升了算法在实际天线阵列中的适用性。仿真结果表明,在信噪比为5 dB、存在单个干扰源的条件下,所提算法能实现低于–40 dB的干扰抑制深度,并将峰值旁瓣电平稳定在–24.5 dB以下,同时减少10%的激活阵元。在与现有方法的定量对比中,该算法在信噪比为5 dB场景下的输出信干噪比相较于最小方差无失真响应方法提升11.37 dB。实验结果证明该框架能够在导向矢量失配及低信噪比等非理想条件下,以较少的阵元实现较高的输出信干噪比和较强的干扰抑制能力,对导向矢量误差与阵元间的相互耦合均表现出良好的鲁棒性。Abstract:
Objective The rapid advancement of modern communication technologies (e.g., 5G networks and IoT applications) has led to increased complexity in signal processing for wireless communication and radar systems. Adaptive beamforming techniques have found extensive applications in these areas owing to their effectiveness in extracting the signal of interest amidst interference and noise. Traditional robust adaptive beamforming methods can effectively handle steering vector mismatch. Such mismatches may arise from environmental non-stationarity, direction-of-arrival estimation errors, imperfect array calibration, antenna deformation, and local scattering effects. However, they ignore the potential benefits of the sparse arrays, which can significantly reduce hardware complexity and system cost. Moreover, they frequently fail to suppress sidelobe levels (SLL) in environments with interference source, limiting their practical utility in complex electromagnetic scenarios. To overcome these limitations, this paper proposes a robust adaptive beamforming algorithm that achieves both the sparse arrays and low SLL constraints. Methods Unlike conventional sparse approaches that place the l0 norm penalty in the objective function, the proposed method introduces the l0 norm into the constraint. This formulation ensures that the optimized array configuration satisfies the pre-specified number of active sensors, thereby avoiding the uncertainty caused by adjusting sparse weights in multi-objective optimization models. In addition to the sparsity constraint, a SLL suppression constraint is also introduced. This design imposes an upper bound on the array response in interference and clutter directions, thereby effectively suppressing undesired signals. By integrating these constraints into the optimization framework, the proposed method achieves a robust Minimum Variance Distortionless Response (MVDR) beamforming that exhibits sparsity, adaptivity, and robustness. To address the nonconvexity of the formulated optimization problem, a convex relaxation strategy is adopted to transform the non-convex constrain into a convex one. Therefore, this paper proposes robust adaptive beamforming methods that generates a sparse weight solution from a uniform linear array (ULA). It is worth noting that although the proposed method is derived from a ULA, obtaining a sparse weight solution provides several practical benefits. By assigning zero weights to certain sensors, the method effectively reduces the number of active elements, lowering hardware cost and computational complexity, while still maintaining desirable beamforming performance. The main contribution of this paper lies in proposing a unified framework that enables collaborative optimization of robustness, beam performance, SLL, and array sparsity. Results and Discussions A series of simulation experiments were conducted to evaluate the performance of the proposed sparse robust beamforming algorithm under various scenarios, including multiple interference environments, steering vector mismatch, angle-of-arrival (AOA) mismatch, low signal-to-noise ratio (SNR) conditions, and complex electromagnetic environments based on practical antenna arrays. Simulation results demonstrate that the proposed algorithm can maintain stable mainlobe gain in the desired signal direction while forming deep nulls in the interference directions. First, in the presence of steering vector mismatch, conventional MVDR beamformers often suffer from reduced mainlobe gain or even beam pointing deviations, which severely compromise the reception of the desired signal. In contrast, the proposed algorithm is capable of maintaining a stable and distortionless mainlobe direction under mismatch conditions, thereby ensuring high gain in the desired signal direction ( Fig. 2(a) ,Fig. 3(a) ). Second, by introducing a sidelobe constraint, the proposed algorithm effectively suppresses clutter and achieves significantly lower peak sidelobe levels compared with other approaches (Fig. 2(b) ). Third, under low-SNR conditions, the algorithm demonstrates strong noise resistance. Even in severely noise-contaminated scenarios, it is able to maintain effective interference suppression and achieve high output Signal-to-Interference-plus-Noise Ratio (SINR). This indicates that the method has good adaptability in weak target detection and in cluttered environments. Moreover, the optimized sparse array configuration achieves beamforming performance close to that of a ULA despite activating only a subset of sensors (Fig. 2 ). Finally, experimental validation based on real antenna arrays further confirmed the effectiveness of the proposed method (Fig. 3 ). The algorithm maintains stable performance and is still able to achieve high gain in the desired direction even in the presence of AOA estimation mismatches (Fig. 4 ). In summary, experimental results demonstrate that the proposed algorithm achieves significant improvements in robustness and hardware efficiency. Furthermore, it exhibits reliable performance and effectiveness in complex electromagnetic environments.Conclusions This paper proposes a robust adaptive beamforming algorithm for sparse arrays. The core innovation lies in establishing a joint optimization model that incorporates array sparsity, steering vector mismatch robustness, and low SLL constraints into a unified framework. Compared with methods such as MVDR[9] (which primarily focuses on interference suppression), CMR[12] (which achieves robustness), or NA-CS[30] (which only achieves array sparsity), the proposed method achieves a balanced across multiple dimensions. Simulation results demonstrate that, in complex scenarios involving steering vector errors, AOA estimation mismatches, and low SNR conditions, this method can maintain satisfactory beamforming performance with lower hardware costs, exhibiting stronger practical engineering value and application potential. -
Key words:
- Adaptive beamforming /
- sparse arrays /
- robust constraints /
- convex optimization
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表 1 各种算法的计算复杂度对比
算法 计算复杂度 主要计算来源 所提算法 $ O\left(\sqrt{N+J}\left({N}^{3}+N{K}^{2}+NJ\right)\right) $ 多约束SOCP内点法求解 MVDR[9] $ O\left({N}^{3}\right) $ 协方差矩阵求逆 CMR[12] $ O\left({N}^{3.5}\right) $ 协方差矩阵重构与优化 NA-CS[30] $ O\left({N}^{2}D+{D}^{3}\right) $ 稀疏重构与字典矩阵构建 注:$ N $是天线个数,$ K $是接收信号的采样点数,$ J $是副瓣区域采样点数,$ D $是离散化空域点数,通常远大于$ N $,导致其实际计算负担较重。 -
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