Direction of arrival (DOA) estimation plays an important role in the passive surveillance system based on troposcatter. Rank deficiency and subspace leakage resulting from multipath propagation can deteriorate the performance of the DOA estimator. In this paper, characteristics of signals propagated by troposcatter are analyzed, and an efficient DOA estimation method is proposed. According to our new method, the invariance property of noise subspace (IPNS) is introduced as the main method. To provide precise noise subspace for INPS, forward and backward spatial smoothing (FBSS) is carried out to overcome rank deficiency. Subspace leakage is eliminated by a two-step scheme, and this process can also largely reduce the computational load of INPS. Numerical simulation results validate that our method has not only good resolution in condition of closely spaced signals but also superior performance in case of power difference.

中文翻译：

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基于对流散射的无源监控系统有效DOA估计方法

到达方向（DOA）估计在基于对流散射的被动监视系统中起着重要作用。由多径传播引起的秩不足和子空间泄漏会降低DOA估计器的性能。本文分析了对流散射传播信号的特性，提出了一种有效的DOA估计方法。根据我们的新方法，引入了噪声子空间（IPNS）的不变性作为主要方法。为了为INPS提供精确的噪声子空间，执行了前向和后向空间平滑（FBSS）以克服秩不足。通过两步方案消除了子空间泄漏，该过程还可以大大减少INPS的计算量。