A Portable Real-Time Digital Noise Radar System for Through-the-Wall Imaging
05 Apr 2012-IEEE Transactions on Geoscience and Remote Sensing (IEEE)-Vol. 50, Iss: 10, pp 4123-4134
TL;DR: A portable, digital, real-time random noise radar system operating in the ultrahigh frequency range for through-the-wall detection and imaging and its capability to image target scenes and characterize human activity from different stand-off distances is demonstrated.
Abstract: We present the design and implementation of a portable, digital, real-time random noise radar system operating in the ultrahigh frequency range for through-the-wall detection and imaging. Noise radar technology is combined with modern digital signal processing approaches to architect a system to covertly perform range imaging of obscured stationary and moving targets as well as to detect the presence of humans via micro-Doppler detection combined with empirical mode decomposition. We model the propagation and sampling nonidealities in the system and propose techniques to overcome the effect of these nonidealities. Experimental results demonstrate the system's capability to image target scenes and characterize human activity from different stand-off distances.
Citations
More filters
TL;DR: In this article, the authors used the empirical mode decomposition to produce a unique feature vector from the human micro-Doppler signals following which a support vector machine was used to classify human motions.
Abstract: The ability to identify human movements can serve as an important tool in many different applications such as surveillance, military combat situations, search and rescue operations and patient monitoring in hospitals. This information can provide soldiers, security personnel and search and rescue workers with critical knowledge that can be used to potentially save lives and/or avoid dangerous situations. Most research involving human activity recognition employs the short-time Fourier transform (STFT) as a method of analysing human micro-Doppler signatures. However, the STFT has time-frequency resolution limitations and Fourier transform-based methods are not well-suited for use with non-stationary and non-linear signals. The authors approach uses the empirical mode decomposition to produce a unique feature vector from the human micro-Doppler signals following which a support vector machine is used to classify human motions. This study presents simulations of simple human motions, which are subsequently validated using experimental data obtained from both an S-band radar and a W-band millimetre wave (mm-wave) radar. Very good classification accuracies are obtained at distances of up to 90 m between the human and the radar.
142 citations
TL;DR: A novel hybrid fusion scheme is proposed to combine soft and hard fusion to push the classification performances to approximately 96% accuracy in identifying continuous activities and fall events.
Abstract: This paper presents a framework based on multi-layer bi-LSTM network (bidirectional Long Short-Term Memory) for multimodal sensor fusion to sense and classify daily activities’ patterns and high-risk events such as falls. The data collected in this work are continuous activity streams from FMCW radar and three wearable inertial sensors on the wrist, waist, and ankle. Each activity has a variable duration in the data stream so that the transitions between activities can happen at random times within the stream, without resorting to conventional fixed-duration snapshots. The proposed bi-LSTM implements soft feature fusion between wearable sensors and radar data, as well as two robust hard-fusion methods using the confusion matrices of both sensors. A novel hybrid fusion scheme is then proposed to combine soft and hard fusion to push the classification performances to approximately 96% accuracy in identifying continuous activities and fall events. These fusion schemes implemented with the proposed bi-LSTM network are compared with conventional sliding window approach, and all are validated with realistic “leaving one participant out” (L1PO) method (i.e. testing subjects unknown to the classifier). The developed hybrid-fusion approach is capable of stabilizing the classification performance among different participants in terms of reducing accuracy variance of up to 18.1% and increasing minimum, worst-case accuracy up to 16.2%.
118 citations
TL;DR: In this paper, the authors present a review of micro-Doppler based on subject type, sensor capabilities, as well as environmental effects, and then propose future research areas for micro doppler.
Abstract: Micro-Doppler signals refer to Doppler scattering returns produced by the motions of the target other than gross translation. The small micro-motions of a subject, and even just parts of a subject, can be observed through the micro-Doppler signature it creates in response to an active emitter such as a radar, laser, and even acoustic emitters. These micro-Doppler signatures are produced by the kinematic properties of the subject's motion and can be used to extract the salient features of the subject's motion, and often, identify the subject. The rapidly declining cost of micro-Doppler-capable active sensors like radar with their dramatically improving capabilities, provide significant motivation in developing micro-Doppler techniques that can improve the exploitation of these sensors. Micro-Doppler techniques aim at extracting the micro-motion of the subject that may be unique to a particular subject class or activity in order to distinguish probable false alarms from real detections, as well as to increase the value of the information extracted from the sensor. The source of micro-motion depends on the subject and can be a rotating propeller on a fixed-wing aircraft, the multiple spinning rotor blades of a helicopter, or an unmanned aerial vehicle (UAV); the vibrations of an engine shaking a vehicle; an antenna rotating on a ship; the flapping wings of birds; the swinging arms and legs of a walking person; and many other sources. Confuser detections, such as birds for UAVs or animals for humans, can be interpreted as false alarms for a sensor system, so using the available micro-Doppler returns for classification can significantly reduce the sensor false alarm rate, thereby improving the utility of the sensor system. This study reviews the current research in micro-Doppler based on subject type, sensor capabilities, as well as environmental effects, and then proposes future research areas for micro-Doppler.
110 citations
TL;DR: A novel dynamic range-Doppler trajectory (DRDT) method based on the frequency-modulated continuous-wave (FMCW) radar system is proposed to recognize continuous human motions with various conditions emulating real-living environment and achieves accurate and robust recognition even in various conditions of distance, view angle, direction, and individual diversity.
Abstract: Radar-based human motion recognition is crucial for many applications, such as surveillance, search and rescue operations, smart homes, and assisted living. Continuous human motion recognition in real-living environment is necessary for practical deployment, i.e., classification of a sequence of activities transitioning one into another, rather than individual activities. In this paper, a novel dynamic range-Doppler trajectory (DRDT) method based on the frequency-modulated continuous-wave (FMCW) radar system is proposed to recognize continuous human motions with various conditions emulating real-living environment. This method can separate continuous motions and process them as single events. First, range-Doppler frames consisting of a series of range-Doppler maps are obtained from the backscattered signals. Next, the DRDT is extracted from these frames to monitor human motions in time, range, and Doppler domains in real time. Then, a peak search method is applied to locate and separate each human motion from the DRDT map. Finally, range, Doppler, radar cross section (RCS), and dispersion features are extracted and combined in a multidomain fusion approach as inputs to a machine learning classifier. This achieves accurate and robust recognition even in various conditions of distance, view angle, direction, and individual diversity. Extensive experiments have been conducted to show its feasibility and superiority by obtaining an average accuracy of 91.9% on continuous classification.
106 citations
Cites background from "A Portable Real-Time Digital Noise ..."
...HUMAN motion recognition has attracted great interest for different purposes, such as surveillance, search and rescue operations, smart home, and senior people care in assisted living facilities [1]–[5]....
[...]
TL;DR: The article shows that this research area is highly active and fast moving and demonstrates that micro-Doppler techniques can provide important solutions to many radar target classification challenges.
Abstract: Target motions, other than the main bulk translation of the target, induce Doppler modulations around the main Doppler shift that form what is commonly called a target micro-Doppler signature. Radar micro-Doppler signatures are generally both target and action specific and hence can be used to classify and recognise targets as well as to identify possible threats. In recent years, research into the use of micro-Doppler signatures for target classification to address many defence and security challenges has been of increasing interest. In this article, we present a review of the work published in the last 10 years on emerging applications of radar target analysis using micro-Doppler signatures. Specifically we review micro-Doppler target signatures in bistatic SAR and ISAR, through-the-wall radar and ultrasound radar. This article has been compiled to provide radar practitioners with a unique reference source covering the latest developments in micro-Doppler analysis, extraction and mitigation techniques. The article shows that this research area is highly active and fast moving and demonstrates that micro-Doppler techniques can provide important solutions to many radar target classification challenges.
91 citations
References
More filters
TL;DR: It has been shown that using multifrequency data high-quality image reconstruction can be achieved with a limited array view.
Abstract: A two-dimensional nonlinear inverse scattering technique is developed for imaging objects in a multilayered medium that simulates the effects of building walls in the context of through-wall imaging (TWI). The effectiveness and capacity of the inversion algorithm and the feasibility of through-wall imaging is demonstrated via a number of numerical examples. It has been shown that using multifrequency data high-quality image reconstruction can be achieved with a limited array view.
301 citations
"A Portable Real-Time Digital Noise ..." refers background in this paper
...Research work by several groups also focused on theoretical aspects, including synthetic aperture radar (SAR) imaging [6], [7], antenna beamforming [8], waveform design [9], Doppler estimation and tracking [10]–[12], tomographic imaging [13]–...
[...]
TL;DR: Computer algorithms for reference signal delay and compression are discussed as replacements for the classical delay line implementation and the ambiguity function and the statistical characteristics of the correlation output for the latter configuration are further analyzed.
Abstract: Pulse compression radar is used in a great number of applications. Excellent range resolution and high electronic counter-countermeasures performance is achieved by wideband long pulses, which spread out the transmitted energy in frequency and time. By using a random noise waveform, the range ambiguity is suppressed as well. In most applications, the random signal is transmitted directly from a noise-generating microwave source. A sine wave, which is phase or frequency modulated by random noise, is an alternative, and in this paper, the ambiguity function and the statistical characteristics of the correlation output for the latter configuration are further analyzed. Range resolution is then improved because the noise bandwidth of the modulated carrier is wider than that of the modulating signal, and the range sidelobes are also further suppressed. Random biphase modulation gives a 4-dB (/spl pi//sup 2//4) improvement, but much higher sidelobe suppression could be achieved using continuous phase/frequency modulation. Due to the randomness of the waveform, the output correlation integral is accompanied by a noise floor, which limits the possible sidelobe suppression as determined by the time-bandwidth product. In synthetic aperture radar (SAR) applications with distributed targets, this product should be large compared with the number of resolution elements inside the antenna main beam. The advantages of low range sidelobes and enhanced range resolution make frequency/phase-modulated noise radar attractive for many applications, including SAR mapping, surveillance, altimetry, and scatterometry. Computer algorithms for reference signal delay and compression are discussed as replacements for the classical delay line implementation.
219 citations
TL;DR: This letter extends the analysis to 3D imaging via delay-and-sum beamforming in the presence of a single uniform wall to provide valuable information on target heights that can be used for enhancing target discrimination/identification.
Abstract: Through-the-wall imaging and urban sensing is an emerging area of research and development. The incorporation of the effects of signal propagation through wall material in producing an indoor image is important for reliable through-the-wall mission operations. We have previously analyzed wall effects, such as refraction and change in propagation speed, and designed a wideband beamformer for 2D imaging using line arrays. In this letter, we extend the analysis to 3D imaging via delay-and-sum beamforming in the presence of a single uniform wall. The third dimension provides valuable information on target heights that can be used for enhancing target discrimination/identification. Supporting simulation results are provided.
195 citations
"A Portable Real-Time Digital Noise ..." refers background in this paper
...Research work by several groups also focused on theoretical aspects, including synthetic aperture radar (SAR) imaging [6], [7], antenna beamforming [8], waveform design [9], Doppler estimation and tracking [10]–[12], tomographic imaging [13]–...
[...]
01 May 1959
TL;DR: The resulting system is similar to existing altimeters but is free of the ambiguities inherent in periodically modulated systems, avoids the "fixed error," and is capable of measuring distances down to a few feet, which makes it particularly suited for use as an altimeter in blind landing systems.
Abstract: Distance measuring systems using random noise as the modulating function are described. The distance measurement is accomplished by correlating the modulation on the transmitted and received signals. The spectrum of the modulating function determines the way in which this correlation, and hence system output, depends on distance to a reflecting target. Physical realizability of filters limits the output-to-distance behavior of linear, noise-modulated systems. Theoretically, either amplitude or frequency modulation can be used, but the latter has distinct advantages in overcoming incidental spurious signals generated within the system. Actual multiplication of signals is avoided through use of a conventional mixer. The resulting system is similar to existing altimeters but is free of the ambiguities inherent in periodically modulated systems, avoids the "fixed error," and is capable of measuring distances down to a few feet. This makes it particularly suited for use as an altimeter in blind landing systems.
163 citations
"A Portable Real-Time Digital Noise ..." refers methods in this paper
...In parallel, noise radar has also been applied widely in recent years, such as ranging [20], velocity estimation [21], polarimetry [22], SAR [23],...
[...]
TL;DR: The unique design features of the ultra-wideband radar system are described, the theoretical foundations of noise polarimetry are developed, experimental evidence of the polarimetric and resolution capa-bilities of the system are provided, and results obtained in subsurfaceprobing applications are demonstrated.
Abstract: Ram M. NarayananYi XuPaul D. HoffmeyerUniversity of Nebraska—LincolnCenter for Electro-OpticsDepartment of Electrical EngineeringLincoln, Nebraska 68588-0511E-mail: rnarayanan@unl.eduJohn O. CurtisU.S. Army Waterways Experiment StationEnvironmental LaboratoryVicksburg, Mississippi 39180-6199Abstract. A novel coherent ultra-wideband radar system operating inthe 1- to 2-GHz frequency range has been developed recently at theUniversity of Nebraska. The radar system transmits white Gaussiannoise. Detection and localization of buried objects is accomplished bycorrelating the reflected waveform with a time-delayed replica of thetransmitted waveform. Broadband dual-polarized log-periodic antennasare used for transmission and reception. A unique signal-processingscheme is used to inject coherence into the system by frequency trans-lation of the ultrawideband signal by a coherent 160-MHz phase-lockedsource prior to performing heterodyne correlation. The system coher-ence allows the extraction of a target’s polarimetric amplitude and phasecharacteristics. This paper describes the unique design features of theradar system, develops the theoretical foundations of noise polarimetry,provides experimental evidence of the polarimetric and resolution capa-bilities of the system, and demonstrates results obtained in subsurfaceprobing applications.
141 citations
"A Portable Real-Time Digital Noise ..." refers background in this paper
...[24], inverse SAR [25], [26], target tracking [27], foliage penetration [28], and subsurface profiling [29]....
[...]