Welcome to Journal of Beijing Institute of Technology

2021 Vol. 30, No. 4

Display Method:
Waveform Design for MIMO Radar with One-Bit DACs via Block-Sparse Semidefinite Relaxation
Tong Wei, Bin Liao
2021, 30(4): 323-339. doi:10.15918/j.jbit1004-0579.2021.067
Abstract:
Multiple-input multiple-output (MIMO) systems which deploy one-bit DACs are attractive in many fields, such as wireless communications and radar. In this paper, the problem of transmit waveform design in MIMO radar system with one-bit DACs is investigated. By appropriately designing the transmitted QPSK signal waveforms, the majority of radiated energy can be focused into the mainlobe region(s) by minimizing the integrated sidelobe to mainlobe ratio (ISMR) of beampattern, such that the intensity of backscattered signals from targets can be enhanced. However, the resulting optimization problem which consists of constrained fractional quadratic problem (CFQP) is noconvex. To tackle this problem, a block-sparse semidefinite relaxation method is first utilized to reformulate the CFQP into a reduced convex semidefinite programming (SDP). Further, a customized interior point algorithm (IPA) is developed to solve the small-scale SDP. Finally, the desirable one-bit transmit waveform sequence can be properly synthesized by using Gaussian randomization method. Numerical simulation results demonstrate that the proposed method offer better performance than the state-of-the-art algorithms.
A Novel Long-Time Coherent Integration Method for Moving Target Detection
Xia Bai, Yan Wang, Juan Zhao, Ran Tao
2021, 30(4): 340-351. doi:10.15918/j.jbit1004-0579.2021.066
Abstract:
Long-time coherent integration (LTCI) can remarkably improve the detection ability of radar for moving target. To increase the processing efficiency, this paper proposes a novel LTCI method based on segment time reversing transform (STRT) and chirp z-transform (CZT). In this method, STRT operation is first presented to estimate the Doppler ambiguity factor, and keystone transform (KT) is used to correct the whole range migration (RM). Then, CZT and non-uniform fast Fourier transform (NUFFT) are used to estimate the parameters as well as correct the second and third order Doppler frequency migration (DFM). Compared with the existing methods, the proposed method can achieve RM correction and DFM correction without repetitive operation. The effectiveness of the proposed method is validated by both simulated and real data.
Tensor-Based Source Localization Method with EVS Array
Guanjun Huang, Yongquan Li, Zijing Zhang, Junpeng Shi, Fangqing Wen
2021, 30(4): 352-362. doi:10.15918/j.jbit1004-0579.2021.020
Abstract:
In many wireless scenarios, e.g., wireless communications, radars, remote sensing, direction-of-arrival (DOA) is of great significance. In this paper, by making use of electromagnetic vector sensors (EVS) array, we settle the issue of two-dimensional (2D) DOA, and propose a covariance tensor-based estimator. First of all, a fourth-order covariance tensor is used to formulate the array covariance measurement. Then an enhanced signal subspace is obtained by utilizing the higher-order singular value decomposition (HOSVD). Afterwards, by exploiting the rotation invariant property of the uniform array, we can acquire the elevation angles. Subsequently, we can take advantage of vector cross-product technique to estimate the azimuth angles. Finally, the polarization parameters estimation can be easily completed via least squares, which may make contributions to identifying polarization state of the weak signal. Our tensor covariance algorithm can be adapted to spatially colored noise scenes, suggesting that it is more flexible than the most advanced algorithms. Numerical experiments can prove the superiority and effectiveness of the proposed approach.
DOA Estimation Based on Subspace Compensation for Unfolded Coprime Array
Jianfeng Li, Xiong Xu, Ping Li, Yawei Tang
2021, 30(4): 363-367. doi:10.15918/j.jbit1004-0579.2021.060
Abstract:
Direction of arrival (DOA) estimation for unfolded coprime array (UFCA) is discussed, and a method based on subspace compensation is proposed. Conventional DOA estimation methods partition the UFCA into two subarrays for separate estimations, which are then combined for unique DOA determination. However, the DOA estimation performance loss is caused as only the partial array aperture is exploited. We use the estimations from one subarray as initial estimations, and then enhance the estimation results via a compensation based on the whole array, which is implemented via a simple least squares (LS) operation constructed from the initial estimation and first-order Taylor expansion. Compared to conventional methods, the DOA estimation performance is improved while the computational complexity is in the same level. Multiple simulations are conducted to verify the efficiency of the proposed approach.
A Singular Value Thresholding Based Matrix Completion Method for DOA Estimation in Nonuniform Noise
Peiling Wang, Jinfeng Zhang
2021, 30(4): 368-376. doi:10.15918/j.jbit.1004-0579.2021.078
Abstract:
Usually, the problem of direction-of-arrival (DOA) estimation is performed based on the assumption of uniform noise. In many applications, however, the noise across the array may be nonuniform. In this situation, the performance of DOA estimators may be deteriorated greatly if the non-uniformity of noise is ignored. To tackle this problem, we consider the problem of DOA estimation in the presence of nonuniform noise by leveraging a singular value thresholding (SVT) based matrix completion method. Different from that the traditional SVT method apply fixed threshold, to improve the performance, the proposed method can obtain a more suitable threshold based on careful estimation of the signal-to-noise ratio(SNR) levels. Specifically, we firstly employ an SVT-based matrix completion method to estimate the noise-free covariance matrix. On this basis, the signal and noise subspaces are obtained from the eigendecomposition of the noise-free covariance matrix. Finally, traditional subspace-based DOA estimation approaches can be directly applied to determine the DOAs. Numerical simulations are performed to demonstrate the effectiveness of the proposed method.
Effective DOA Estimation Under Low Signal-to-Noise Ratio Based on Multi-Source Information Meta Fusion
Yun Wu, Xiukun Li, Zhimin Cao
2021, 30(4): 377-396. doi:10.15918/j.jbit1004-0579.2021.052
Abstract:
Efficiently performing high-resolution direction of arrival (DOA) estimation under low signal-to-noise ratio (SNR) conditions has always been a challenge task in the literatures. Obviously, in order to address this problem, the key is how to mine or reveal as much DOA related information as possible from the degraded array outputs. However, it is certain that there is no perfect solution for low SNR DOA estimation designed in the way of winner-takes-all. Therefore, this paper proposes to explore in depth the complementary DOA related information that exists in spatial spectrums acquired by different basic DOA estimators. Specifically, these basic spatial spectrums are employed as the input of multi-source information fusion model. And the multi-source information fusion model is composed of three heterogeneous meta learning machines, namely neural networks (NN), support vector machine (SVM), and random forests (RF). The final meta-spectrum can be obtained by performing a final decision-making method. Experimental results illustrate that the proposed information fusion based DOA estimation method can really make full use of the complementary information in the spatial spectrums obtained by different basic DOA estimators. Even under low SNR conditions, promising DOA estimation performance can be achieved.
DOA Estimation Method Using Sparse Representation with Orthogonal Projection
Fujia Xu, Aifei Liu, Shiqi Mo, Song Li
2021, 30(4): 397-402. doi:10.15918/j.jbit.1004-0579.2021.062
Abstract:
In order to reduce the effect of noises on DOA estimation, this paper proposes a direction-of-arrival (DOA) estimation method using sparse representation with orthogonal projection (OPSR). The OPSR method obtains a new covariance matrix by projecting the covariance matrix of the array data to the signal subspace, leading to the elimination of the noise subspace. Afterwards, based on the new covariance matrix after the orthogonal projection, a new sparse representation model is established and employed for DOA estimation. Simulation results demonstrate that compared to other methods, the OPSR method has higher angle resolution and better DOA estimation performance in the cases of few snapshots and low SNRs.
An Active Anti-Jamming Approach for Frequency Diverse Array Radar with Adaptive Weights
Yibin Liu, Chunyang Wang, Guimei Zheng, Jian Gong
2021, 30(4): 403-411. doi:10.15918/j.jbit1004-0579.2021.0065
Abstract:
Due to the rapid development of electronic countermeasures (ECMs), the corresponding means of electronic counter countermeasures (ECCMs) are urgently needed. In this paper, an active anti-jamming method based on frequency diverse array radar is proposed. By deriving the closed form of the phase center in a uniform line array FDA, we establish a model of the FDA signal based on adaptive weights and derive the effect of active anti-jamming in this regime. The proposed active anti-jamming method makes it difficult for jammers to detect or locate our radar. Furthermore, the effectiveness of the two frequency increment schemes in terms of anti-jamming is analyzed by comparing the deviation of phase center. Finally, the simulation results verify the effectiveness and superiority of the proposed method.
Wideband Direction-of-Arrival Estimation Based on Deep Learning
Liya Xu, Yi Ma, Jinfeng Zhang, Bin Liao
2021, 30(4): 412-424. doi:10.15918/j.jbit1004-0579.2021.079
Abstract:
The performance of traditional high-resolution direction-of-arrival (DOA) estimation methods is sensitive to the inaccurate knowledge on prior information, including the position of array elements, array gain and phase, and the mutual coupling between the array elements. Learning-based methods are data-driven and are expected to perform better than their model-based counterparts, since they are insensitive to the array imperfections. This paper presents a learning-based method for DOA estimation of multiple wideband far-field sources. The processing procedure mainly includes two steps. First, a beamspace preprocessing structure which has the property of frequency invariant is applied to the array outputs to perform focusing over a wide bandwidth. In the second step, a hierarchical deep neural network is employed to achieve classification. Different from neural networks which are trained through a huge data set containing different angle combinations, our deep neural network can achieve DOA estimation of multiple sources with a small data set, since the classifiers can be trained in different small subregions. Simulation results demonstrate that the proposed method performs well both in generalization and imperfections adaptation.
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