Zhen Liu

National University of Defense Technology | NUDT · Department of Electronic Science and Technology

The private and indiscriminate flying of low-altitude unmanned aerial vehicles (UAVs) seriously violates human privacy and airspace traffic safety. In this work, we propose a low-altitude UAV detection system based on the programmable metasurface-enabled 4-D radar, mounted on an unmanned ground vehicle (UGV). For the first time, we utilize this sim...

High Resolution Range Profiles (HRRPs) have become a key area of focus in the domain of Radar Automatic Target Recognition (RATR). Despite the success of deep learning based HRRP recognition, these methods needs a large amount of training samples to generate good performance, which could be a severe challenge under non‐cooperative circumstances. Cu...

The fundamental challenge in SAR target detection lies in developing discriminative, efficient, and robust representations of target characteristics within intricate non-cooperative environments. However, accurate target detection is impeded by factors including the sparse distribution and discrete features of the targets, as well as complex backgr...

Occlusion is a longstanding difficulty that challenges the UAV-based object detection. Many works address this problem by adapting the detection model. However, few of them exploit that the UAV could fundamentally improve detection performance by changing its viewpoint. Active Object Detection (AOD) offers an effective way to achieve this purpose....

Transfer-based targeted adversarial attacks against black-box deep neural networks (DNNs) have been proven to be significantly more challenging than untargeted ones. The impressive transferability of current SOTA, the generative methods, comes at the cost of requiring massive amounts of additional data and time-consuming training for each targeted...

In this paper, we introduce a dual-metasurface based imaging radar deception jamming system to address the inherent angular sensitivity of metasurface in radar signal modulation. In this proposed architecture, two metasurfaces are integrated with their respective horn antennas to form the radio frequency transceiver components responsible for echo...

This article proposes a novel module called middle spectrum grouped convolution (MSGC) for efficient deep convolutional neural networks (DCNNs) with the mechanism of grouped convolution. It explores the broad “middle spectrum” area between channel pruning and conventional grouped convolution. Compared with channel pruning, MSGC can retain most of t...

A sparsity-based adaptive beamforming (ABF) method is introduced to effectively process coherent signals with polarized sensor arrays (PSA). This method exploits the spatial sparsity of observed signals by transforming it into row-sparsity within a waveform-polarization composite matrix through data reorganization. This row-sparsity is subsequently...

This paper investigates the problem of directionof-arrival (DoA) estimation based on sparse recovery (SR). Unlike convex relaxation-based SR methods, the reweighted atomic minimization (RAM) introduces a non-convex sparsity metric that enhances sparsity and resolution. However, it solely embeds the log-det penalty and exhibits parameter redundancy....

Target misalignment can cause beam pointing deviations and degradation of sidelobe performance. In order to eliminate the effect of target misalignment, we formulate the jamming sub-space recovery problem as a linearly modified atomic norm-based optimization. Then, we develop a deep-unfolding network based on the alternating direction method of mul...

Recently, deep unfolding networks have been widely used in direction of arrival (DOA) estimation because of their improved estimation accuracy and reduced computational cost. However, few have considered the existence of a nested array (NA) with off-grid DOA estimation. In this study, we present a deep sparse Bayesian learning (DSBL) network to sol...

Recently, deep unfolded networks have been widely utilized in direction of arrival (DOA) estimation due to the reduced computational complexity and improved estimation accuracy. However, few consider the nested array for off-grid DOA estimation, where the estimated DOAs are not on the prespecified grids. In this article, we propose a deep unfolded...

Multipath signals are commonly encountered in complex electromagnetic environments, resulting in the failure of traditional adaptive beamforming (ABF) due to signal cancellation. Various methods have been proposed to tackle this problem, but most of them are subject to multiple restrictions such as specific array geometries or requirements for prio...

In the case of multipath propagation for passive bistatic radar (PBR) using uncooperative frequency agile-phased array radar as an illuminator, a new direction-finding method is proposed to deal with the scenario where the coherent and uncorrelated signals are closely spaced or in the same direction. Firstly, spatial difference technique is used to...

Recently, deep unfolding networks with interpretable parameters have been widely utilized in direction of arrival (DOA) estimation due to the faster convergence speed and better generalization ability. However, few consider the nested array for gridless DOA estimation. In this letter, we propose a deep alternating projection network to address the...

Owing to the large degrees of freedom and reduced mutual coupling by generating difference coarrays, nonuniform linear arrays have aroused great interest in direction of arrival estimation. Previous works have shown some improved sparse arrays, while few find the common features hidden within these structures. In this paper, we define a generic-coa...

In this letter, a wideband programmable metasurface, which consists of 20 × 20 1 b reflection unit cells, is designed and fabricated to perform radar one-dimensional range profile (ODRP) dynamic jamming. The quasi-butterfly reflection element soldering p-i-n diode is proposed to realize reflection phase difference of 170° ± 10° between the on and...

In this paper, the convolution neural networks (CNN) are developed for the classification and localization of mixed near-field and far-field sources by using the geometry of symmetric nested array. We first transform the received data into frequency domain. Then, we preprocess the phase difference matrix to decouple mixed sources. Considering that...

Coprime arrays (CPAs) have been found to be an effective configuration for adaptive beamforming (ABF). However, most ABF methods for CPAs are embedded with the spatial spectrum estimation technique, and therefore they usually deteriorate in the case of low signal-to-noise ratio (SNR), especially without prior information of interferences. To addres...

We present the convolution neural networks (CNNs) to achieve the localization of near-field sources via the symmetric double-nested array (SDNA). Considering that the incoherent near-field sources can be separated in the frequency spectrum, we first calculate the phase difference matrices and consider the typical elements as the inputs of the netwo...

In an era of ubiquitous large-scale evolving data streams, data stream clustering (DSC) has received lots of attention because the scale of the data streams far exceeds the ability of expert human analysts. It has been observed that high-dimensional data are usually distributed in a union of low-dimensional subspaces. In this article, we propose a...

In this paper, we employ the geometry of uniform circular array to achieve classification and localization of mixed near-field and far-field sources. Considering that the eigendecomposition of the covariance matrix requires high computational cost, we develop the propagator method to obtain the noise subspace and reduce complexity. Firstly, since t...

Recent research treats radar emitter classification (REC) problems as typical closed-set classification problems, i.e., assuming all radar emitters are cooperative and their pulses can be pre-obtained for training the classifiers. However, such overly ideal assumptions have made it difficult to fit real-world REC problems into such restricted model...

One-bit quantization has become an important topic in modern signal processing. In this letter, we consider the problem of three dimensional (3-D) source localization by combining one-bit quantized measurements and the phase-based algorithm under a uniform circular array (UCA). With analysis, unquantized and one-bit quantized cross-correlation coef...

Deep-learning generative methods have developed rapidly. For example, various single- and multi-view generative methods for meshes, voxels, and point clouds have been introduced. However, most 3D single-view reconstruction methods generate whole objects at one time, or in a cascaded way for dense structures, which misses local details of fine-grain...

As one of the most important features for human perception, contours are widely applied in graphics and mapping applications. However, it is considerably challenging to extract contours from large-scale point clouds due to the irregular distribution of point clouds. In this letter, we propose a 3-D-guided multiconditional residual generative advers...

We present a second-order statistics (SOS)-based algorithm for three-dimensional (3-D) localization of multiple near-field sources using an uniform circular array (UCA). Based on the centro-symmetric property of UCA steering vectors, a particular diagonal matrix, which only includes two-dimensional (2-D) direction of arrival (DOA) is constructed by...

Coherent source localization is a common problem in signal processing. In this paper, a sparse representation method is considered to deal with two-dimensional (2D) direction of arrival (DOA) estimation for coherent sources with a uniform circular array (UCA). Considering that objective function requires sparsity in the spatial dimension but does n...

Traditional localisation technologies for wideband linear frequency modulation (LFM) source are always confined to the far‐field situation and suffer from high computational cost for dealing with multiple sub‐narrowband components. In this study, by performing temporal delay‐and‐correlation to wideband LFM signals, a fast and closed‐form algorithm...

Cross-eye jamming is an angular deception jamming technique against monopulse radar. Multiple-element retrodirective cross-eye jamming (MRCJ) as an improved method, uses a retrodirective antenna array with multiple antenna elements in a cross-eye jammer and can obtain better jamming performance. However, the practical MRCJ system employing a linear...

Constructive solid geometry (CSG) is a technique to create a complex 3D object by using boolean operators to combine simple primitives. However, it is very challenging to obtain programs from 3D models, the inverse of the constructing process. In this Letter, the authors propose a generative recursive network for the inverse problem, which is compo...

The generation of 3D models from a single image has recently received much attention, based on which point cloud generation methods have been developed. However, most current 3D reconstruction methods only work for relatively pure backgrounds, which limits their applications on real images. Meanwhile, more fine-grained details are required to provi...

Under uniform circular array, by employing some algebraic schemes to exploit the phase information of receiving data and further estimate the source’s three-dimensional (3D) parameters (azimuth angle, elevation angle, and range), a series of novel phase-based algorithms with low computational complexity have been proposed recently. However, when th...

With the development of the laser scanning technique, it is easier to obtain 3D large-scale scene rapidly. However, many scanned objects may suffer serious incompletion caused by the scanning angles or occlusion, which has severely impacted their future usage for the 3D perception and modeling, while traditional point cloud completion methods often...

A key problem within data mining is clustering of data streams. Most existing algorithms for data stream clustering are based on quite restrictive models for the cluster dynamics. In an attempt to overcome the limitations of existing methods, we propose a novel data stream clustering method, which we refer to as improved streaming affinity propagat...

A high-accuracy algorithm is presented for the localization of mixed incoherent near-field and far-field narrow-band sources under uniform circular array (UCA). Herein, considering that it is difficult to classify the mixed sources, we first decouple mixed sources’ angles and ranges by calculating centro-symmetric sensors’ phase differences. Then,...

This paper focuses on developing an anti-velocity jamming strategy that enhances the ability of a pulse-Doppler (PD) radar to detect moving targets in the presence of translational and/or micro motion velocity jamming generated by the digital radio frequency memory (DRFM) repeat jammers. The strategy adopts random pulse initial phase (RPIP) pulses...

Interrupted sampling repeater jamming (ISRJ) is an effective way of deceiving coherent radar sensors, especially for linear frequency modulated (LFM) radar. In this paper, for a simplified scenario with a single jammer, we propose a dynamic electronic counter-counter measure (ECCM) scheme based on jammer parameter estimation and transmitted signal...

Due to its widespread application in communications, radar, etc., the orthogonal frequency division multiplexing (OFDM) signal has become increasingly urgent in the field of localization. Under uniform circular array (UCA) and near-field conditions, this paper presents a closed-form algorithm based on phase difference for estimating the three-dimen...

Localization of linear frequency modulation (LFM) source based on combination of time_ frequency analysis and spatial spectrum estimation technique has received extensive research. However, this scheme is always confined to far-field sources and suffers from high computational cost. In this letter, by performing the fractional Fourier transform (FR...

Localization of a source whose half-wavelength is smaller than the array aperture would suffer from serious phase ambiguity problem, which also appears in recently proposed phase-based algorithms. In this paper, by using the centro-symmetry of fixed uniform circular array (UCA) with even number of sensors, the source’s angles and range can be decou...

Intra-pulse frequency coded (IPFC) signal, with its large time-bandwidth and low probability of interception characteristics, is widely applied to anti-jamming radar system. This paper focuses on the efficiency of interrupted sampling repeater jamming (ISRJ) under IPFC signal, and the influence on jamming effect with different signal forms and wave...

Random Pulse Repetition Interval Compressed Sensing Radar (RPRICSR) has superiorities on target detection, unambiguous velocity measurement as well as anti-velocity jamming for its signal randomness. However, RPRICSR cannot detect the micro motion targets effectively under the presence of micro motion false targets within present echo processing me...

Under fixed uniform circular array (UCA), 3-D parameter estimation of a source whose half-wavelength is smaller than the array aperture would suffer from a serious phase ambiguity problem, which also appears in a recently proposed phase-based algorithm. In this paper, by using the centro-symmetry of UCA with an even number of sensors, the source’s...

Source localization with an array is an important topic for wireless communication, radar, sonar, etc. In order to resolve the phase ambiguity in parameter estimation of a single high frequency near-field source with uniform circular array (UCA), a rotation-based algorithm is introduced to make the same sensor form virtual short base-line. First, a...

Imaging precession targets based on the narrowband radar to distinguish the real warhead from mid-course targets is a new technique in missile defense systems. Aiming at the typical mid-course flying scene, this paper describes the principle of the narrowband imaging method, and analyzes the influence on the narrowband imaging by the target transla...

When the random pulse repetition interval (RPRI) compressed sensing radar suffers from the jamming of active velocity false target, the sparsity of target echoes will be destroyed and the RPRI compressed sensing radar's superiority on target detection and velocity measurement will be limited. In practice, due to the random modulation, the jammers c...

Near-field source localization suffers from serious phase ambiguity, when the array aperture is larger than half-wavelength. In this letter, by performing adaptive rotation of uniform circular array (UCA) with a center sensor, a closed-form algorithm based on phase difference is improved for estimating the source’s 3-D location (azimuth angle, elev...

In order to resolve the phase ambiguity in parameter estimation of a high frequency source with uniform circular array (UCA), this paper presents an algorithm via clustering to obtain the source’s 3-D parameters (azimuth angle, elevation angle, and range) unambiguously. By computing the phase differences between centro-symmetric sensors and employi...

The effect of platform skin return on multiple-element retrodirective cross-eye jamming (MRCJ) system is investigated, allowing the differences between multiple jammer loops to be considered. The jammer antennas employ a linear array with a common center. The median value of the total cross-eye gain and the jamming-to-signal ratio (JSR) are derived...

Low-frequency long-range radars (LFLRRs) are assumed to lack the ability of extracting targets micro motion signature, due to their low and nonuniform track update rate, as well as the weak micro Doppler (m-D) owing to their large wave length. The recently proposed sinusoidal frequency modulated (SFM) Fourier transform can achieve a longer integral...

For random pulse initial phase radar, the echo signal of false velocity target which is emitted by digital radio frequency memory (DRFM) repeat jammer always lags several pulse repetition interval (PRI) behind that of true target in terms of pulse initial phase. Consequently, the lag causes the difference in phase at the same PRI, and it provides t...

In existing sparsity-driven inverse synthetic aperture radar (ISAR) imaging framework a sparse recovery (SR) algorithm is usually applied to azimuth compression to achieve high resolution in the cross-range direction. For range compression, however, direct application of an SR algorithm is not very effective because the scattering centers resolved...

This paper focuses on the high resolution time-frequency distribution (TFD) of multicomponent signals with amplitude and frequency modulations, and a concise method named short-time sparse representation (STSR) is proposed. In STSR, both analysis and synthesis of the discrete signal can be achieved by exploiting the signal’s sparsity in frequency d...

Random stepped-frequency radar without delay-Doppler coupling can suppress the range ambiguity and become less sensitive to electronic countermeasures. Considering its inherent randomness, this paper focuses on sidelobe reduction in inverse synthetic aperture radar imaging for sparse target scenes based on the compressed sensing (CS) theory. First,...

The intricate vibration of a working vehicle provides an important signature to the vehicle type. Small vibrations introduce phase modulation in radar echoes, which is referred to as micro-Doppler (m-D) phenomenon and can be modeled as sinusoidal frequency-modulated (SFM) signal. Such phase modulation induced by vibrations consists of multiple freq...

Compressed sensing has been applied to achieve high resolution range profiles (HRRPs) using a stepped-frequency radar. In this new scheme, much fewer pulses are required to recover the target's strong scattering centers, which can greatly reduce the coherent processing interval (CPI) and improve the anti-jamming capability. For practical applicatio...

Narrowband radar has been successfully used for high resolution imaging of fast rotating targets by exploiting their micro-motion features. In some practical situations, however, the target image may suffer from aliasing due to the fixed pulse repetition interval (PRI) of traditional radar scheme. In this work, the random PRI signal associated with...

Time-frequency distribution (TFD) has been widely used for micro-Doppler analysis in radar signal processing. However, the spectrogram will suffer from aliasing if the maximum Doppler frequency exceeds half of the pulse repetition frequency, which may lead to false estimation of the targets' kinematic properties. In this study, by transmitting a se...

In this letter, the relationship between target scattering function and point spread function of radar tomographic imaging is discussed, and an inherent super-resolution reconstruction algorithm based on image decomposition (ID) is proposed. By removing the cross disturbance due to the resolution limitation, the exact radar images can be obtained....