Coprime arrays have shown desirable properties in reducing mutual coupling and increasing degrees of freedom (DOF) compared to uniform linear arrays (ULAs), which helps improve the estimation performance. However, the holes in the difference coarray of coprime arrays cause estimation performance loss. In this paper, we present a multi-layer holes filling strategy for coprime arrays to fill the holes, thus enhancing the uniform difference coarray. Specifically, we first construct a coprime array with multiple duplicated subarrays (CAMDS) and classify the holes in the difference coarray into multiple layers. Then we present a multi-layer filled coprime array (MLFCA) by introducing extra subarrays to fill the holes in different layers, which resultantly achieves significantly increased uniform DOFs (uDOFs). We then derive the optimal MLFCA in the scale of difference coarray and develop an optimized structure to extend the difference coarray. Finally, the proposed coprime arrays enjoy a hole-free difference coarray and achieve a larger uniform difference coarray than previous coprime arrays. Simulation results have verified the merits of the proposed coprime arrays through the subspace-based estimator.

This paper presents a new technique for estimating the two-dimensional direction of departure (2D-DOD) and direction of arrival (2D-DOA) in bistatic uniform planar array Multiple-Input Multiple-Output (MIMO) radar systems. The method is based on the reduced-dimension (RD) MUSIC algorithm, aiming to achieve improved precision and computational efficiency. Primarily, this pioneering approach efficiently transforms the four-dimensional (4D) estimation problem into two-dimensional (2D) searches, thus reducing the computational complexity typically associated with conventional MUSIC algorithms. Then, exploits the spatial diversity of array response vectors to construct a 4D spatial spectrum function, which is crucial in resolving the complex angular parameters of multiple simultaneous targets. Finally, the objective is to simplify the spatial spectrum to a 2D search within a 4D measurement space to achieve an optimal balance between efficiency and accuracy. Simulation results validate the effectiveness of our proposed algorithm compared to several existing approaches, demonstrating its robustness in accurately estimating 2D-DOD and 2D-DOA across various scenarios. The proposed technique shows significant computational savings and high-resolution estimations and maintains high precision, setting a new benchmark for future explorations in the field.

Position determination algorithms of rectilinear emitters (also called strictly second-order non-circular emitters) with multiple sensor arrays (SAs) allow for higher localization accuracy and more achievable degrees of freedom compared to the conventional version with circular emitters. However, it also brings additional computational complexity and noise. In this paper, we develop a position determination algorithm of rectilinear emitters in closed-form on the basis of phase alignment and optimal weighted least square (OWLS), which is termed as PAOWLS method. Firstly, we utilize polynomial root-finding method to obtain angle of arrival (AOA) and estimate rectilinear phases to align AOA. Then we construct a least square (LS) constraint to estimate positions of emitters directly (termed as PALS method). Finally, we construct a weighted LS constraint and deduce the optimal weight to compensate the position estimation bias. Extensive numerical results verify the outstanding performance of the proposed algorithm in terms of localization accuracy, resolution capability, and computational complexity.

Signal detection is a serious challenge for uplink massive multiple-input multiple-output (MIMO) systems. The traditional linear minimum-mean-squared error (MMSE) achieves good detection performance for such systems, but involves matrix inversion, which is computationally expensive due to a large number of antennas. Thus, several iterative methods such as Gauss–Seidel (GS) have been studied to avoid the direct matrix inversion required in the MMSE. In this paper, we improve the GS iteration in order to enhance the detection performance of massive MIMO systems with a large loading factor. By exploiting the property of massive MIMO systems, we introduce a novel initialization strategy to render a quick start for the proposed algorithm. While maintaining the same accuracy of the designed detector, the computing load is further reduced by initialization approximation. In addition, an effective preconditioner is proposed that efficiently transforms the original GS iteration into a new one that has the same solution, but a faster convergence rate than that of the original GS. Numerical results show that the proposed algorithm is superior in terms of complexity and performance than state-of-the-art detectors. Moreover, it exhibits identical error performance to that of the linear MMSE with one-order-less complexity.