Yimin D. Zhang

Temple University | TU · Department of Electrical and Computer Engineering

In this paper, we analyze the effect of sensor placement to the achievable number of degrees-of-freedom (DOFs) when the sensors deviate from a half-wavelength grid. More specifically, we consider two variations of a uniform linear array (ULA), namely, when one or more sensors are shifted from half-wavelength grid positions and when the inter-elemen...

In this paper, we consider the conditions for unique identifiability of the direction-of-arrival (DOA) estimation problem under a multi-frequency sparse rational array framework. Previous studies on the multi-frequency scenario involved integer locations of the virtual sensor locations at each frequency. The rational array framework removes such re...

In this paper, we analyze the Cramer-Rao bound of the distributed direction-of-arrival (DOA) estimation problem where the covariance matrix is formulated in a mixed-precision manner. In this scheme, the self-covariance matrix of a subarray is locally computed using the full-precision data received at the subarray, whereas one-bit data are exploited...

Distributed sparse arrays, consisting of multiple subarrays, facilitate a higher number of degrees of freedom and enhanced direction-of-arrival (DOA) estimation performance beyond what is offered by single uniform linear arrays. When the array elements in each subarray are sparsely located, the covariance matrix is sparse with missing entries. Cova...

In this paper, we present a novel direction-of-arrival (DOA) estimation strategy that exploits distributed sparse sensor arrays and structured matrix completion-based information fusion techniques to provide superior DOA estimation performance with enhanced degrees-of-freedom. We consider a sparse array consisting of a plurality of distributed suba...

Time-Frequency Signal Analysis and Processing (TFSAP) is a collection of theory and algorithms used for analysis and processing of nonstationary signals, as found in a wide range of applications including telecommunications, radar, and biomedical engineering. This book brings together the main knowledge of TFSAP, from theory to applications, in a u...

We propose novel joint radar-communication spectrum sharing strategies exploiting orthogonal frequency-division multiplexing (OFDM) waveforms that concurrently achieve the objectives of both radar and communication systems. An OFDM transmitter is considered that transmits dual-purpose OFDM sub-carriers such that all the sub-carriers are exploited f...

In this paper, we develop a general framework of multi-frequency sparse array to estimate the direction-of-arrival (DOA) of a significantly higher number of targets than the number of physical sensors. The multi-frequency sparse arrays are designed to offer zero lag redundancy in the rendered difference coarray so that the available degrees of free...

Modern medical devices exploit radio frequency (RF) communication to remotely perform vital communication services for medical purposes. Real-time monitoring of health parameters, transferring of patient data to a data center or a cell phone, and controlling other medical devices are some of the important applications in medical science which explo...

In this paper, we propose a robust strategy to localize multiple ground sources exploiting a distributed unmanned aerial vehicle (UAV) network in the presence of impulse noise. We achieve robust source localization by using 1-principal component analysis (1-PCA) based signal subspace estimation at each individual UAV. This approach significantly re...

In this paper, we propose a robust strategy to localize multiple ground sources exploiting a distributed unmanned aerial vehicle (UAV) network in the presence of impulse noise. We achieve robust source localization by using l1-principal component analysis (l1-PCA) based signal subspace estimation at each individual UAV. This approach significantly...

The conventional coprime array consists of two uniform linear subarrays to construct an effective difference coarray with desirable characteristics. Such linear coprime arrays only provide one-dimensional (1-D) direction-of-arrival (DOA) estimation. In this paper, we propose a novel coprime array configuration with parallel subarrays, along with an...

In this paper, we present a novel joint radar-communication system which exploits orthogonal frequency division multiplexing (OFDM) waveforms for performing radar and communication operations simultaneously. A dual-purpose OFDM transmitter is exploited which optimizes the transmit power of different sub-carriers to fulfill the radar objectives. The...

This paper utilizes sparse array motion to increase the numbers of achievable both degrees of freedom (DOFs) and consecutive lags in direction-of-arrival (DOA) estimation problems. We use commonly employed environment-independent sparse array configurations. The design of these arrays is not dependent on the sources in the field of view, but rather...

As the most promising technology in wireless communications, massive multiple-input multiple-output (MIMO) faces a significant challenge in practical implementation because of the high complexity and cost involved in deploying a separate front-end circuit for each antenna. In this paper, we apply the compressive sampling technique to reduce the num...

In this paper, we address the problem of instantaneous frequency (IF) estimation of non-linear, multi-component frequency modulated (FM) signals in the presence of burst missing data samples, where different signal components have distinct amplitude levels. Burst missing data induce significant artifacts in the time-frequency (TF) representations o...

Massive multiple-input multiple-output (MIMO) is one of the most promising techniques for next generation wireless communications due to its superior capability to provide high spectrum and energy efficiency. Considering the very large number of antennas employed at the base station, however, the pilot overhead for downlink channel estimation becom...

Radio astronomical observations are increasingly contaminated by radio frequency interference (RFI), rendering the development of effective RFI suppression techniques a pressing task. In practice, the existence of model mismatch makes the observing environment more challenging. In this paper, we develop a robust astronomical imaging method in the p...

Recently, nested and coprime arrays have attracted considerable interest due to their capability of providing increased array aperture, enhanced degrees of freedom (DOFs), and reduced mutual coupling effect compared to uniform linear arrays (ULAs). These features are critical to improving the performance of DOA estimation and adaptive beamforming....

We develop a novel radar-based human motion recognition technique that exploits the temporal sequentiality of human motions. The stacked recurrent neural network (RNN) with long short-term memory (LSTM) units is employed to extract sequential features for automatic motion classification. The spectrogram of raw radar data is used as the network inpu...

A novel dilated nested array is presented to obtain an enhanced fully filled difference co-array exploiting array motions. The proposed sparse array is suitable for the cases when the sensing environment can be assumed stationary over an array motion of half wavelength or shorter. Closed-form expressions of the number of degrees of freedom in the d...

In this paper, a compressed sensing (CS)-based joint estimation of direction of arrival (DoA) and polarization parameters is proposed using a sparse array consisting of dual-polarized antenna elements. Since this joint estimation with the CS as well as conventional subspace based methods turn out to be computationally prohibitive, we propose a nove...

Electrical impedance tomography (EIT) is developed to investigate the internal conductivity changes of an object through a series of boundary electrodes, and has become increasingly attractive in a broad spectrum of applications. However, the design of optimal tomography image reconstruction algorithms has not achieved the adequate level of progres...

In this paper, we present an effective time-frequency (TF) analysis of non-stationary frequency modulated (FM) signals in the presence of burst missing data samples. The key concept of the proposed work lies in the reliable sparse recovery of non-parametric FM signals in the joint-variable domains. Specifically, by utilizing the one-dimensional Fou...

A novel robust adaptive beamforming algorithm based on a coprime array is proposed in this study. First, the authors exploit the virtual array structure of the coprime coarray to construct two subspaces. The first subspace is obtained from the covariance matrix of the virtual uniform linear array, whereas the second one is obtained by integrating a...

Spectrum sharing using a joint platform for radar and communication systems has attracted significant attention in recent years. In this paper, we propose a novel dual-function radar-communications (DFRC) strategy to embed quadrature amplitude modulation (QAM) based communication information in the radar waveforms by exploiting sidelobe control and...

Sparse arrays, such as nested arrays and coprime arrays, can achieve a high number of degrees of freedom (DOFs) for direction of arrival (DOA) estimation with a reduced number of antennas. On the other hand, the compressive measurement method provides an effective way to reduce the number of front-end circuit chains. In this paper, we generalized c...

Modern radio telescopes commonly use antenna arrays, and high-resolution imaging techniques exploiting radio astronomical signals collected at these antenna arrays play a critical role to achieve their missions. Beamforming techniques have been developed in radio astronomy to generate dirty images with limited image resolutions for many years. Beca...

In this paper, we address the problem of spectrum estimation of multiple frequency-hopping (FH) signals in the presence of random missing observations. The signals are analyzed within the bilinear time-frequency (TF) representation framework, where a TF kernel is designed by exploiting the inherent FH signal structures. The designed kernel permits...

In this paper, we propose direction-of-arrival (DOA) estimation techniques, respectively based on covariance matrix reconstruction and matrix completion, to achieve robust DOA estimation capability in nonuniform noise environments using coprime arrays. For the covariance matrix reconstruction-based approach, by exploring the diagonal structure of t...

Sparse arrays can achieve a higher number of degrees of freedom (DOFs) compared with uniform linear array (ULA) counterparts. To further reduce the number of physical sensors while keeping a high number of DOFs, a direction of arrival (DOA) estimation algorithm by exploiting coprime frequencies base on a sparse ULA is recently proposed. However, th...

This paper addresses the detection of weak astronomical signals that are contaminated by strong frequency-hopping (FH) interferers and suffer from missing samples. The problem is considered in the time-frequency domain and we successively suppress artifacts due to missing samples, estimate and remove FH interferers, and detect the weak astronomical...

Conventionally, sparsity-aware multi-sensor multi-target tracking (MTT) algorithms comprise a two-step architecture that cascades group sparse reconstruction and MTT algorithms. The group sparse reconstruction algorithm exploits the apriori information that the measurements across multiple sensors share a common sparse support in a discretized targ...

Real-time locating systems require high localization accuracy in the order of a few centimeters. Conventional methods for radio frequency identification (RFID) localization fail to achieve such accuracy, particularly in complex radio frequency propagation environments. In this paper, we propose a method for locating and tracking an RFID reader that...

In this paper, we propose a robust direction-ofarrival (DOA) estimation algorithm in the context of sparse reconstruction, where some array sensors are mis-calibrated. In this case, conventional DOA estimation algorithms suffer from degraded performance or even failed operations. In the proposed approach, the mis-calibrated sensor observations are...

Compared to a uniform linear array with the same number of physical sensors, a coprime array has a larger array aperture as well as increased degrees-of-freedom (DOFs). Therefore, in a practical wireless communication system, it is capable to provide desirable performance with a low computational complexity. In this paper, we focus on the problem o...

In this paper, we propose a novel sparse array design for direction-of-arrival estimation based on the fourth-order statistics of the received signals. The utilization of fourth-order statistics provides a higher number of degrees of freedom and flexibility as compared to the commonly used covariance-based methods. The proposed sparse array design...

Compared to a uniform linear array with the same number of physical sensors, a coprime array has a larger array aperture as well as increased degrees-of-freedom (DOFs). Therefore, in a practical wireless communication system, it is capable to provide desirable performance with a low computational complexity. In this paper, we focus on the problem o...

Quadrature compressive sampling (QuadCS) is a sub-Nyquist sampling scheme for acquiring in-phase and quadrature (I/Q) components in radar. In this scheme, the received intermediate frequency (IF) signals are expressed as a linear combination of time-delayed and scaled replicas of the transmitted waveforms. For sparse IF signals on discrete grids of...

Passive radar systems operate by exploiting signals of opportunity that are designed for other applications, such as broadcasting, communications, and satellite navigation. Passive radars have recently attracted attention in military applications, mainly because of their covertness, low-cost implementation, and no requirement of signal emissions [1...

Group sparsity based method is applied to the 2q-th order difference co-array for underdetermined wideband direction of arrival (DOA) estimation. For complexity reduction, a focused compressive sensing based approach is proposed, without sacrificing its performance. Different from the conventional focusing approach, in the proposed one, focusing is...

It has been shown that analog-to-information con- version (AIC) is an efficient scheme to perform sub-Nyquist sampling of pulsed radar echoes. However, it is often impractical, if not infeasible, to reconstruct full-range Nyquist samples because of huge storage and computational load requirements. Based on the analyses of AIC measurement system, th...

In this paper, we propose a robust direction-of-arrival (DOA) estimation algorithm based on group sparse reconstruction algorithm utilizing signals observed at multiple frequencies. The group sparse reconstruction scheme for DOA estimation is solved through the complex multitask Bayesian compressive sensing algorithm by exploiting the group sparse...

Different from conventional phased-array radars, the frequency diverse array (FDA) radar offers a rangedependent beampattern capability that is attractive in various applications. The spatial and range resolutions of an FDA radar are fundamentally limited by the array geometry and the frequency offset. In this paper, we overcome this limitation by...

We propose a nonstationary jammer signal suppression technique based on parametric sparse reconstruction, where sparsely sampled data are considered. By assuming nonstationary jammers that are characterized by polynomial phase signatures, a data-dependent parametric dictionary matrix is designed. In order to obtain an accurate instantaneous frequen...

Increased demand on spectrum sensing over a broad frequency band requires a high sampling rate and thus leads to a prohibitive volume of data samples. In some applications, e.g., spectrum estimation, only the second-order statistics are required. In this case, we may use a reduced data sampling rate by exploiting a low-dimensional representation of...

The last decade witnessed a growing demand on radio frequency that is driven by technological advances benefiting the end consumer but requiring new allocations of frequency bandwidths. Further, higher data rates for faster communications and wireless connections have called for an expanded share of existing frequency allocations. Concerns for spec...

We use the phase difference among sensors, by solving the phase wrapping problem based on the cross-spectrum between sensors, to obtain the DOA without exhaustive search in the 2D angle space. The proposed approach does not need the typical sensor separation or inter-frequency separation requirements. Simulation results with narrowband, wideband si...

Automatic detection of pavement cracks is an important task in transportation maintenance for driving safety assurance. However, it remains a challenging task due to the intensity inhomogeneity of cracks and complexity of the background, e.g., the low contrast with surrounding pavement and possible shadows with similar intensity. Inspired by recent...

A one-bit joint sparse representation direction of arrival (OBJSR-DOA) estimation approach is proposed in this letter. By exploiting the joint spatial and spectral correlations inherent in acoustic sensor array data, the proposed OBJSR-DOA approach provides reliable DOA estimation from only the sign bit of randomly subsampled acoustic sensor data....

In this paper, we develop a new technique for information embedding into the emission of multiple-input multiple-output (MIMO) radar using dual-functionality platforms. A set of orthogonal waveforms occupying the same band is used to implement the primary MIMO radar operation. The secondary communication function is implemented by embedding one pha...

In this paper, we consider the problem of tracking multiple targets in a passive multi-static radar system using Doppler-only measurements. The number of targets is assumed unknown and time-varying. The Doppler measurements are subject to additive noise, clutter, and missed detections. Doppler-only measurements from a single sensor provide incomple...

We propose a new scheme to estimate the directions-of-arrival (DOAs) of mixed coherent and uncorrelated targets exploiting a collocated multiple-input multiple-output (MIMO) radar with transmit/receive coprime arrays. In the proposed scheme, the DOAs of the uncorrelated targets are first estimated using subspace-based methods, whereas those of the...

A wideband off-grid model is proposed to represent dictionary mismatch under the compressive sensing framework exploiting difference co-arrays. A group sparsity based off-grid method is proposed for underdetermined wideband direction of arrival (DOA) estimation which provides improved performance over the existing group sparsity based method with a...

The co-prime array, which utilizes a co-prime pair of uniform linear sub-arrays, provides a systematical means for sparse array construction. By choosing two co-prime integers M and N, co-array elements can be formed from only physical sensors. As such, a higher number of degrees-of-freedom (DOFs) is achieved, enabling direction-of-arrival (DOA) es...

The essence of amplitude-modulation based dual-function radar-communications is to modulate the sidelobe of the transmit beampattern while keeping the main beam, where the radar function takes place, unchanged during the entire processing interval. The number of distinct sidelobe levels (SLL) required for information embedding grows exponentially w...

Recently, dual-function radar-communications (DFRC) has been proposed as means to mitigate the spectrum congestion problem. Existing amplitude-shift keying (ASK) methods for information embedding do not take full advantage of the highest permissable sidelobe level. In this paper, a new ASK-based signaling strategy for enhancing the signal-to-noise...

Frequency-hopping (FH) is one of the commonly used spread spectrum techniques that finds wide applications in communications and radar systems due to its capability of low probability of intercept, reduced interference, and desirable ambiguity property. In this paper, we consider the blind estimation of the instantaneous FH spectrum without the kno...

In this paper, we propose a nonstationary jammer suppression method for GPS receivers when the signals are sparsely sampled. Missing data samples induce noise-like artifacts in the time-frequency (TF) distribution and ambiguity function of the received signals, which lead to reduced capability and degraded performance in jammer signature estimation...

Micro-Doppler interference generated by mechanical vibration or rotation of a target or its parts may degrade the quality of radar images. In this paper, a method based on histogram analysis of the time-frequency distribution is proposed for enhanced radar image reconstruction with effective micro-Doppler interference removal. First, based on the d...

This paper establishes the role of sparse arrays and sparse sampling in antijam global navigation satellite systems (GNSS). We show that both jammer direction of arrival estimation methods and mitigation techniques benefit from the design flexibility of sparse arrays and their extended virtual apertures or coarrays. Taking advantage of information...

The authors develop a novel phase-modulation based dual-function system with joint radar and communication platforms. A bank of transmit beamforming weight vectors is designed such that they form the same transmit power radiation patterns, whereas the phase associated with each transmit beam towards the intended communication directions belongs to...