Wall Radar Research Articles

Development of a model of received signals and algorithms for their processing for radar detection of people in rooms through a wall

The problem of developing models of received radar signals in through a wall sensing radars is considered, taking into account the properties of targets and the presence of interference clutter. In this case, the targets to be detected are people who are in a mobile or stationary state. It is assumed that the sensing is carried out using an ultra-wideband signal with step frequency modulation. The developed model should correspond to the actual received signals of the through a wall radar in terms of the proximity of statistical characteristics. Goal of article – creation of models of reflected signals corresponding to sensing with the help of through a wall radar of various rooms in the presence or absence of living people in them. Signal models have been developed that correspond to the cases of probing both an "empty" room (in the absence of people) and a room with people inside it. When developing models, the properties of real signals that were obtained during field experiments with the radar layout are taken into account. The statistical characteristics of real and model signals are compared, as a result of which the adequacy of the developed models to real signals is shown. It is also shown that the amplitude of the complex envelope of the target signal can be described using the Gauss function. The developed signal models make it possible to determine the characteristics of a matched filter, the use of which in signal processing in through-the-wall radar leads to a significant reduction in the noise component and smoothing of signals. With the help of the developed models, estimates of the effectiveness of signal processing algorithms can be obtained for various scenarios of probing rooms through a wall.

A 0.9 - 1.5 GHz CMOS UWB Radar IC for Through the Wall Human Detection

In this paper, a UWB radar IC for the through wall radar is presented to achieve the smaller form factor of the module and low power operation. For the penetration performance enhancement, the radar IC s designed for the lower 0.9 – 1.5 GHz band. The radar IC employs the 4-channel time-interleaved equivalent time sampling receiver for 200 ps fine resolution, and the digitally synthesized impulse generator for the transmitter. The human target behind the concrete brick wall can be detected in the distance over 9.4 m with the help of signal processing part and additional amplifiers. The radar transceiver IC is fabricated in a 0.13 μm CMOS technology and the current consumption is 116.3 mA at the 1.2 V supply.

A New Clutter Elimination and Downrange Correction Algorithm for Through Wall Radar Detection

A New Clutter Elimination and Downrange Correction Algorithm for Through Wall Radar Detection

Sensor Arrangement in Through-the Wall Radar Imaging

In this paper, the problem of how to spatially sample the scattered field in microwave through-the wall imaging is addressed. To this end, a two-dimensional scalar configuration for a three-layered back-ground medium is considered under a linearized scattering model. The aim is to collect as low as possible measurements by maintaining the same performance in the reconstructions. Accordingly, the number and the positions of the spatial measurement points are determined so that the point-spread function of the resulting semi-discrete problem approximates well the one of the ideal continuous case (i.e., when data space is not sampled at all). It is shown that the resulting measurement spatial positions must be non-uniformly arranged across the measurement domain and their number is generally much lower than the one returned by some literature sampling criteria. Also, the measurement points can be analytically determined by taking into account the geometrical parameters as well as the wall features. Numerical examples are included to check the theoretical arguments.

Cancellation of Matched Filter Sidelobes for LFM Radar using Regularized Orthogonal Matching Pursuit

Major disadvantage of matched filter is with sidelobes as they might cause false alarms or may mask weak targets of radar echo. In applications like Urban sensing, Through the wall radar, Non destructive testing etc small objects of interest play crucial role which might be masked by sidelobes of matched filter or sometimes sidelobes may be mistreated as objects of interest that lead to false alarms. Many solutions have been proposed in the literature to suppress these sidelobe levels to some extent but not completely cancelled. In this paper, a new approach is utilized to completely cancel the sidelobes of matched filter using a greedy algorithm known as Regularized Orthogonal Matching Pursuit (ROMP). This algorithm is applied to the matched filter output that resulted in complete removal of sidelobes. Also SNR is improved. Even at very low SNRs targets are detected with high probability and hence the proposed approach is more robust to noise.

Corrigendum: Improved vital signal extraction algorithm for through the wall radar

Corrigendum: Improved vital signal extraction algorithm for through the wall radar

Improved vital signal extraction algorithm for through the wall radar

The vital signal extraction remains an on-going challenge due to the low signal-to-noise ratio (SNR) of vital signals in real tests. In this Letter, the authors propose a novel vital signal enhancement method using spectral gain instead of the traditional singular value decomposition (SVD) method, which shows excellent performance in the elimination of noise that is in the same frequency band as the vital signal and reducing calculation time. The simulation and experiment have been conducted, and the results indicate that the proposed extraction method outperforms the traditional SVD in output SNR and processing time.

Development of Optimal Thresholding Technique for Shape and Size Detection for Through the wall Radar Imaging System

Through-the-wall radar (TWR) images of stationary target behind a wall are subject to strong stationary and non-stationary clutter which obscures the target position and size in the image. Stationary clutters are present due to strong reflection from the wall and non-stationary clutter occurs due to multipath, noise, etc. A lot of work has been reported for mitigating stationary clutter successfully for various real scenarios. However, for mitigating nonstationary clutter various authors have reported their work in this field but any concrete result has not been reported so far. Hence, there is a need for an optimal methodology to mitigate non-stationary clutter in TWR images for achieving a high-quality image representing the target position, shape and its size. Till now it is difficult to achieve shape detection of the target from the TWR system. Therefore, in this paper, a novel optimal thresholding technique is proposed to mitigating non-stationary clutter for further enhancement on shape detection of a target using curve fitting and genetic algorithm. The proposed methodology gives a satisfactory result and can prove to be a powerful technique for minimising clutter.

On the Application of Digital Moving Target Indication Techniques to Short-Range FMCW Radar Data

In this paper, we describe three digital moving target indication (MTI) and moving target segmentation techniques (based on target speed) and apply them to short-range frequency-modulated continuous wave (FMCW) radar data. The described approaches are applicable to many short-range radar sensors. In particular, we focus on FMCW radar, which are ubiquitous in numerous applications, including gesture recognition radar, automotive radar, and imaging radar. The three digital MTI filtering methods explored are background subtraction, finite impulse response (FIR) filtering, and infinite impulse response (IIR) filtering. Each of the methods is implemented in the time domain for simpler logic implementation. We apply the MTI methods on data sets gathered using a C-band FMCW radar in both a short-range, direct line-of-sight scenario and a complex cluttered through wall radar scenario. Based on the analyses, it is shown that each of the MTI techniques are extremely effective when deployed in the right scenario. Background subtraction is found to be well suited for slow-moving targets. FIR and IIR filtering techniques provide the simplest, one-step processes for moving target segmentation.

DESIGN AND PROTOTYPE OF A COMPACT, ULTRA WIDE BAND DOUBLE RIDGED HORN ANTENNA FOR BEHIND OBSTACLE RADAR APPLICATIONS

In this paper, we propose an ultrawide band design for the double ridged horn (DRH) antenna to be used behind the obstacle radar (BOR) applications such as ground penetrating radar (GPR) and through the wall radar (TWR) imaging. The design is developed and optimized by the help of full electromagnetic simulator code; CST. The design parameters such as frequencies of operation and the half power beam width (HPBW) are taken into account by considering the BOR application requirements. The design double ridged horn antenna provides a frequency bandwidth between 1.5 GHz and 7 GHz and HPBW around 30° around the center frequency that are very suitable for GPR and TWR applications. The final optimized design that is formed by CST is physically manufactured and measured. The prototyped DRH antenna’s measurement antenna parameter results are in good agreement with the simulated ones.

Remote sensing of vital sign of human body with radio frequency

Medical technology has improved remarkably in the field of health monitoring over the past few decades, becoming more sophisticated and less invasive as the years progress. Now, non-contact measurement of respiration and heartbeat with microwave Doppler radar phase modulation, offers an attractive alternative to commonly prescribed chest strap monitors. To monitor the vital signs an unmodulated radio frequency signal is transmitted toward the human body, where it is phase-modulated by the periodic physiological movement and reflected back to the receiver. The radar receiver captures the reflected signal and demodulates it to extract the vital sign signal components. The reflected signal from the body depends on the radar cross section (RCS) of body. In this paper the RCS of human body is measured in the X-band (8–12 GHz). There are several advantages to a noncontact measurement method: physically, it neither confines nor inhibits the subject and does not cause discomfort or skin irritation as electrodes and straps do. By measuring heartbeats, this technology can also be used to detect a person’s presence, search-and-rescue for earthquake or fire victims and border patrol. It has also attracted the interest of organizations requiring high security, such as see-through- wall radar and airport security monitoring.

Through Wall Radar Classification of Human Micro-Doppler Using Singular Value Decomposition Analysis.

The ability to detect the presence as well as classify the activities of individuals behind visually obscuring structures is of significant benefit to police, security and emergency services in many situations. This paper presents the analysis from a series of experimental results generated using a through-the-wall (TTW) Frequency Modulated Continuous Wave (FMCW) C-Band radar system named Soprano. The objective of this analysis was to classify whether an individual was carrying an item in both hands or not using micro-Doppler information from a FMCW sensor. The radar was deployed at a standoff distance, of approximately 0.5 m, outside a residential building and used to detect multiple people walking within a room. Through the application of digital filtering, it was shown that significant suppression of the primary wall reflection is possible, significantly enhancing the target signal to clutter ratio. Singular Value Decomposition (SVD) signal processing techniques were then applied to the micro-Doppler signatures from different individuals. Features from the SVD information have been used to classify whether the person was carrying an item or walking free handed. Excellent performance of the classifier was achieved in this challenging scenario with accuracies up to 94%, suggesting that future through wall radar sensors may have the ability to reliably recognize many different types of activities in TTW scenarios using these techniques.

A Fast Time-Delay Calculation Method in Through-Wall-Radar Detection Scenario

In TWR (Through Wall Radar) signal processing procedure, time delay estimation is one of the key steps in target localization and high resolution imaging. In time domain imaging procedure such as back projection imaging algorithm, round trip propagation time delay at the path of “transmitter-target-receiver” needs to be calculated for each pixel in imaging region. In typical TWR scenario, transmitter and receiver are at one side and targets at the other side of a wall. Based on two-dimensional searching algorithm or solving two variables equation of four times, traditional time delay calculation algorithms are complex and time consuming, and cannot be used to real-time imaging procedure. In this paper, a new fast time-delay (FTD) algorithm is presented. Because of that incident angle at one side equals to refracting angle at the other side, an equation of lateral distance through the wall can be established. By solving this equation, the lateral distance can be obtained and total propagation time delay can be calculated subsequently. Through processing simulation data, the result shows that new algorithm can be applied effectively to real-time time-delay calculation in TWR signal processing.

Study of RF Propagation Losses in Homogeneous Brick and Concrete Walls using Analytical Frequency Dependent Models

The prediction of wall losses is a fundamental aspect in the development of ultra-wideband throughthe-wall (TTW) detection systems. Accurate ultra-wideband signal attenuation prediction has always been very difficult due to a broad variety of building materials without the support of a sophisticated model. In this paper, the attenuation of different types of concrete and brick walls are estimated using the electromagnetic characteristics of building materials for frequencies from 1 to 5 GHz by two theoretical models based on the method of general solutions of wave equations using boundary conditions and the impedance transformation method or the method of transmission line analogy. This estimation will enable in the design of any ultra wideband through-the wall radar system.

Joint Wall Reflection Suppression and Parameters Estimation for MIMO TWR Imaging

In this paper, a Singular Value Decomposition (SVD)-based method is proposed to jointly suppress wall reflections and estimate the wall parameters, including permittivity and thickness, which are then applied for Multiple-Input Multiple-Output (MIMO) Through Wall Radar (TWR) imaging. However, the wall reflections are collected at different sample points, which caused by the different distances of transmitters and receivers. Firstly, we aligned the received signals at the same reference point to solve this problem. The target and wall reflections will be separated by the SVD based method. Then a mathematical model between wall parameters and wall reflections can be established. We can estimate wall parameters through the mathematical model. Results of targets imaging based on estimated values are proved that the method is feasible.

Through the Wall Radar Imaging with MIMO beamforming processing - Simulation and Experimental Results

In this paper, we address the problem of Through The Wall (TTW) detection with the emerging radar concept that is the Multiple-Input Multiple-Output (MIMO) radar. At first, near field and through the wall propagation effects on electromagnetic waves are adressed then a MIMO frequency signal model is given and the advantages of a MIMO scheme for the complex task of TTW detection is discussed. Then image formation with beamforming processing is derived. Finally, the proposed imaging method is implemented on numerical signals obtained by FDTD computations considering through cinder blocks walls propagation. The obtained images for a scenario with one or two targets are presented. Then the experimental setup is exposed and the realised MIMO radar prototype is described. Finally, experimental results of radar imaging through a cinder block wall are shown.

A New Tracking and Imaging Algorithm of Moving Target for Ultra Wideband Through Wall Radar

近场区域的非接触式穿墙目标跟踪成像探测是超宽带脉冲雷达在火灾救援、安全保卫、城市巷战以及生命威胁等方面的一个重要应用。基于超宽带脉冲雷达的边界散射变换和直接散射波形提取的边界估计算法(SEABED)由于其不适用于穿墙条件下运动目标的成像与跟踪的情况，该文结合SEABED算法的成像原理，提出回波时延差关系曲线概念从而利用三角定位原理和坐标转换实现运动目标的成像与跟踪。文中提出的算法假设在近场条件下，针对运动目标场景建立系统模型，通过成像结果和速度值的同时估计，对墙体背后的运动目标的边界和轨迹进行有效估计。仿真结果表明，该算法能够弥补墙体对目标回波的影响，精确度高，达到穿墙目标跟踪成像探测的目的。

TWO-DIMENSIONAL DIFFRACTION TOMOGRAPHIC ALGORITHM FOR THROUGH-THE-WALL RADAR IMAGING

In this paper, a two-dimensional (2D) difiraction tomographic algorithm based on the flrst order Born approximation is proposed for the imaging of hidden targets behind the wall. The spectral expansion of the three layered background medium Green's function is employed to derive a linear relationship between the spatial Fourier transforms of the image and the received scattered fleld. Then the image can be e-ciently reconstructed with inverse Fast Fourier Transform (IFFT). The linearization of the inversion scheme and the easy implementation of the algorithm with FFT/IFFT make the difiraction tomographic algorithm suitable in through-the- wall radar imaging (TWRI) applications concerning the diagnostics of large probed domain and allow real-time processing. Numerical and experimental results are provided to show the efiectiveness and high e-ciency of the proposed difiraction tomographic algorithm for TWRI.

Sensing and Identifying the Improvised Explosive Device Suicide Bombers: People Carrying Wires on their Body

We examined the use of radar to detect humans wearing detonation wires as part of a suicide vest in suicide bombings in an effort to stop the bombing. Dogaru et al. (Computer models of the human body signature for sensing through the wall radar applications. Tech. Rpt. ARL-TR-4290, Army Research Laboratory, 2007) used numerical electromagnetic simulations to show ways to use radar backscatter to detect humans carrying weapons behind walls. We developed Numerical Electromagnetic Code (NEC) simulations for the radar cross-section of wire configurations appropriate to the human body and compared them to the radar cross-section simulations for the human body done by Dogaru et al. We also used GunnPlexer Doppler radar at 12.5 GHz to collect laboratory experimental data from standoff distances of 2—8 meters from the following: human subjects, human subjects wearing a wire loop, and human subjects wearing a simulated vest with wire loops. We performed numerous experiments with both horizontal and vertical polarization (HH and VV), analyzing the data after each experimental run. We developed metrics from examining our experimental data of the radar cross-sections that could be used in building models to more accurately find subjects wearing wires. We wanted a metric to provide us with better statistical detection rates. We found several metrics that improved our ability to detect persons wearing wires. We discovered our best metric was the VV/HH ratio of radar cross-section. From our empirical modeling, we found that the ratio for people wearing wires was statistically different from people without wires at a level of significance of α = 0.05. Using this metric, we built a Monte Carlo simulation model that generated a crowd of people and randomly picked those with wires on their person. We used our metric and a threshold value, which we determined experimentally, to distinguish the persons with wires from those without wires. We found from our simulation that our metric provided a success rate of detecting persons wearing wires of approximately 83.4%, based on running 36,000 trial runs in Excel. The rate of false alarms, where the metric in the simulation model picked a subject who was not wearing wires as a suspect wearing wires, was reduced to 28%. Using the work of Dogaru et al. and our NEC simulations of wire harnesses in the 0.85—1 GHz range, we found that the radar cross-section ratio (body with wires/body without wires) varied from 11 dB for 1—1.15 GHz VV polarization to —5.5 dB for 0.85—1 GHz HH polarization. This frequency range was the best in the range 0.5—9 GHz. From our research we showed that we can be successful in finding viable metrics for detecting wires on people using radar observations. This preliminary research and the exciting results it produced encourages one to think that suicide bombers can be found prior to their detonation of their bombs and at ranges that are relatively safe.

EVALUATION OF TRM IN THE COMPLEX THROUGH WALL ENVIRONMENT

Practical interests arising from behind-the-wall target detection, surveillance and reconnaissance etal. claim for high capability of imaging in complicated environments. Time Reversal Mirror (TRM) technique, making use of the principle of reciprocity, emerges as a promising way to deal with such complex problem. In this paper, we investigate TRM in the ultra-wideband (UWB) through wall radar imaging (TWRI) through numerical simulation. The probing region is a square room, with walls of rough surface and random media parameters. TRM is used to image the target settled in the room. We evaluate the degradation of the images when the aperture of the array is decreased or the received signals are contaminated by noises. The back projection (BP) algorithm is employed here as a comparison for imaging quality. For the case in which the random walls are changed between the forward and inverse phase of time reversal, we check the imaging stability and applied an averaged Green's function to improve the imaging quality. Finally, some interesting conclusions are drawn.