Radar Module Research Articles

Improving heart rate variability information consistency in Doppler cardiogram using signal reconstruction system with deep learning for Contact-free heartbeat monitoring

A contact-free continuous heart rate variability (HRV) analysis is required to conduct daily heart monitoring and minimize physical contact during medical remedies owing to COVID-19. This paper suggests a Doppler cardiogram (DCG) signal processing and reconstruction system that enables the standard deviation of normal-to-normal peaks (SDNN) obtained from DCG to be used as an actual HRV index. The heartbeat signals of twelve healthy adults were recorded. Three electrodes and a Doppler radar module were used to record the electrocardiogram (ECG) and DCG signals, respectively. To optimize the performance of the signal reconstruction system, two signal processing methods were applied to the dataset. These DCG signals were reconstructed into a signal that mimicked the ECG using a variational autoencoder (VAE), to enhance the consistency of the SDNN. The synthetic signal quality was assessed by comparing the SDNN of the synthetic ECG with that of the reference ECG. A total of 1,430 signals were reconstructed to achieve a valid SDNN. A unified analysis of the signal reconstruction results using different signal processing methods was built up to raise the consistency growth. The final result of the signal reconstruction system represented a consistency improvement of 75.5%, compared to the SDNN of the input DCG.

A Low-Power High-Accuracy Urban Waterlogging Depth Sensor Based on Millimeter-Wave FMCW Radar.

The method of making precise measurements of remote water depth using mmWave technology has great potential for preventing urban waterlogging. To achieve waterlogging prevention, the mmWave system needs to measure the water depth change accurately with a short acquisition time. This paper demonstrates a new accurate mmWave water depth measurement system based on Frequency Modulated Continuous Wave (FMCW) Radar with a center frequency of 77 GHz. To improve distance resolution and lower acquisition time, the Swept Frequency-Cross Correlation (SFCC) algorithm is proposed for the first time to improve the distance computation resolution by 9× and lower time complexity from to compared to traditional FFT-based FMCW radar distance computation. A prototype system equipped with a humidity sensor, a processor module and TI’s FMCW radar module is designed for monitoring urban floods in cities. Using the prototype system with the proposed SFCC, the depth measurement error is reduced from 4.5 cm to less than 5 mm, compared to the default radar post-processing algorithm embedded in the radar module.

Reinforcement Learning-Based UAVs Resource Allocation for Integrated Sensing and Communication (ISAC) System

Due to the limited ability of a single unmanned aerial vehicle (UAV), group unmanned aerial vehicles (UAVs) have attracted more attention in communication and radar fields. The use of an integrated sensing and communication (ISAC) system can make communication and radar modules share a radar module’s resources, coupled with efficient resource allocation methods. It can effectively solve the problem of inadequate UAV resources and the low utilization rate of resources. In this paper, the resource allocation problem is addressed for group UAVs to achieve a trade-off between the detection and communication performance, where the ISAC system is equipped in group UAVs. The resource allocation problem is described by an optimization problem, but with group UAVs, the problem is complex and cannot be solved efficiently. Compared with the traditional resource allocation scheme, which needs a lot of calculation or sample set problems, a novel reinforcement-learning-based method is proposed. We formulate a new reward function by combining mutual information (MI) and the communication rate (CR). The MI describes the radar detection performance, and the CR is for wireless communication. Simulation results show that compared with the traditional Kuhn Munkres (KM) or the deep neural network (DNN) methods, this method has better performance with the increase in problem complexity. Additionally, the execution time of this scheme is close to that of the DNN scheme, and it is better than the KM algorithm.

Design of a Millimeter-Wave Radar Remote Monitoring System for the Elderly Living Alone Using WIFI Communication.

In response to the current demand for the remote monitoring of older people living alone, a non-contact human vital signs monitoring system based on millimeter wave radar has gradually become the object of research. This paper mainly carried out research regarding the detection method to obtain human breathing and heartbeat signals using a frequency modulated continuous wave system. We completed a portable millimeter-wave radar module for wireless communication. The radar module was a small size and had a WIFI communication interface, so we only needed to provide a power cord for the radar module. The breathing and heartbeat signals were detected and separated by FIR digital filter and the wavelet transform method. By building a cloud computing framework, we realized remote and senseless monitoring of the vital signs for older people living alone. Experiments were also carried out to compare the performance difference between the system and the common contact detection system. The experimental results showed that the life parameter detection system based on the millimeter wave sensor has strong real-time performance and accuracy.

MIMO Radar Aided mmWave Time-Varying Channel Estimation in MU-MIMO V2X Communications

Robust channel estimation in time-varying channels is used to guarantee the quality of communication services, especially for Vehicle-to-Everything (V2X) scenarios. To improve the channel estimation accuracy and reduce the pilot overhead, multi-input multi-output (MIMO) radar is deployed to assist millimeter wave (mmWave) channel estimation. In this paper, we propose a MIMO radar aided channel estimation scheme using deep learning (DL) for the uplink mmWave multiuser (MU)-MIMO communications. To allocate pilot resources reasonably, we design a transmission frame structure of joint radar module and communication module, which divides the estimation scheme into two stages, i.e., the arrival/departure (AoA/AoDs) estimation stage and the gain estimation stage. In view of the imperfections of array elements in practice, we propose an AoA/AoDs estimation algorithm based on subspace reconstruction in the AoA/AoDs estimation stage named two-step angle estimation (TSAE) algorithm. In the gain estimation stage, a DL based channel gain estimator is designed. An autoencoder combined with residual structure named residual denoising autoencoder (RDAE) is proposed to eliminate the noise on wireless signals, which is passed into the least square (LS) estimation module to obtain gains. Simulation results demonstrate that the MIMO radar aided and DL-based channel estimator provides the efficient estimation performance of the high-mobility mmWave channel with fewer training resources.

A Study of Detection of Drowsiness and Awakeness using Non-contact Radar Sensors

Biometric information is used in a variety of industrial fields. Heart rate and respiration rate, in particular, are widely applied not only in medical institutions but also in life safety. However, a sensor must be worn or directly attached to the human body to obtain a bio signal, which is inconvenient and limits its application. In this study, a 24 GHz radar sensor module is developed, and an algorithm is implemented by analyzing the frequency and peak values of a human participant’s heartbeat and respiration signals in an unconstrained state. In the experiment, the existing ECG equipment (MP150) and radar sensor module are compared. The results indicate that the average value of MP150 is higher than that of the Doppler sensor in terms of all parameters; however, the deviation of the Doppler sensor is small, and the bias is low. Furthermore, it is confirmed that the HRV decreases in the drowsy state compared to that in the wakeful state in both devices. These results confirm that bio-signals change during drowsiness, and conversely, drowsiness can be detected through changes in bio-signals, which is a significant finding.

Millimeter-Wave Radar Scheme With Passive Reflector for Uncontrolled Blind Urban Intersection

Modern millimeter-wave automotive radars are employed to keep a safe distance between vehicles and reduce the collision risk when driving. Meanwhile, an on-board radar module is supposed to operate in the line-of-sight condition, which limits its sensing capabilities in intersections with obstructed visibility. Therefore, this paper investigates the scheme with passive reflector, enabling the automotive radar to detect an approaching vehicle in the non-line-of-sight (blind) urban intersection. First, extensive radar measurements of the backscattering power are carried out with the in-house assembled millimeter-wave radar equipment. Next, the measured data is employed to calibrate an accurate analytical model, deduced and described in this paper. Finally, the analytical models are deployed to define the optimal parameters of the radar scheme in the particular geometry of the selected intersection scenario. Specifically, it is found that the optimal angular orientation of the reflector is 43.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , while the 20 m curvature radius shows better performance compared to a flat reflector. Specifically, the curved convex shape increases scattering power by 20 dB in the shadow region and, thus, improves the detection probability of the vehicle, approaching the blind intersection.

Analysis and Validation of a Hybrid Forward-Looking Down-Looking Ground Penetrating Radar Architecture

Ground Penetrating Radar (GPR) has proved to be a successful technique for the detection of landmines and Improvised Explosive Devices (IEDs) buried in the ground. In the last years, novel architectures for safe and fast detection, such as those based on GPR systems onboard Unmanned Aerial Vehicles (UAVs), have been proposed. Furthermore, improvements in GPR hardware and signal processing techniques have resulted in a more efficient detection. This contribution presents an experimental validation of a hybrid Forward-Looking–Down-Looking GPR architecture. The main goal of this architecture is to combine advantages of both GPR architectures: reduction of clutter coming from the ground surface in the case of Forward-Looking GPR (FLGPR), and greater dynamic range in the case of Down-Looking GPR (DLGPR). Compact radar modules working in the lower SHF frequency band have been used for the validation of the hybrid architecture, which involved realistic targets.

Design and implementation of distance measurement system based on FMCW technology

In this paper, the distance information is obtained according to the relationship between distance and beat frequency in FMCW ranging principle, the ranging process of sawtooth wave as frequency modulation signal is described in detail, and the causes of ranging error are analyzed briefly. The distance measurement system of simulation uses Matlab software to write, and the hardware ranging platform is built by DB77M24A6426V2 millimeter wave radar module. It is verified that the distance measurement system design in this paper achieves more accurate ranging in the short distance measurement, and provides a relatively simple ranging waveform, which provides a relatively powerful reference basis for the subsequent ranging system design and hardware selection.

A 77-GHz 8RX3TX Transceiver for 250-m Long-Range Automotive Radar in 40-nm CMOS Technology

An automotive 77-GHz long-range radar (LRR) with an 8-channel receiver (RX) and a 3-channel transmitter (TX) in 40-nm CMOS technology is presented. It integrates a 38.5-GHz phase-locked loop (PLL), a transmitter power detector (DET) and power calibration loop, a crystal oscillator (XO), built-in-self-test (BIST) circuits, an SRAM, an eFuse, a temperature compensation calibration loop with a lookup table (LUT) and a temperature sensor, a serial peripheral interface (SPI), and a multiple-input multiple-output (MIMO) control logic. The receiver shows a noise figure (NF) of 8.7 dB and input-referred 1-dB compression point (IP1-dB) of -7.4 dBm. The NF and IP1-dB under the worst conditions are 14 dB and -10 dBm, respectively. The transmitter shows output power of 14.1 dBm and phase noise of -116 dBc/Hz at a 12.5-MHz offset frequency, which corresponds to the frequency of 250-m objects for the fast-chirp frequency-modulated continuous wave (FMCW) radar. The proposed radar module utilizes two transmitter channels for horizontal detection. A 2 × 8 time-division-multiplexing MIMO (TDM-MIMO) technique provides a detection range of 250 m.

Multiphase Continuous-Wave Doppler Radar With Multiarc Circle Fitting Algorithm for Small Periodic Displacement Measurement

A multiphase continuous-wave (MPCW) Doppler radar with a multiarc circle fitting (MACF) algorithm is proposed for improving the accuracy of small periodic displacement measurements. In the proposed radar, local oscillator (LO) signals with different phases are incident to multiple I/Q mixers, to simultaneously generate multiarcs for small periodic motions. The multiarcs obtained from the synchronized data are used in the circle fitting method to provide dc offset compensation, for accurate phase demodulation. The proposed MACF algorithm, based on the Levenberg–Marquardt method, can more precisely compensate for the dc offset by combining multiarcs generated from the proposed radar. A 5.8-GHz MPCW Doppler radar module with four-phased LO signals is implemented as a demonstration. The small periodic displacement of a metal plate on a single-axis linear stage is measured using the proposed radar module and algorithm. Compared with conventional CW Doppler radar using a single arc, measurement results using the proposed radar show that the root-mean-square error (RMSE) can be effectively decreased in the periodic motion from 1 to 2 mm, at distances from 30 to 60 cm. The RMSE is reduced by more than 33% for a peak-to-peak displacement of 1 mm at a distance of 60 cm.

A W-Band Single-Antenna FMCW Radar Transceiver With Adaptive Leakage Cancellation

This article presents a leakage cancellation architecture for single-antenna frequency-modulated continuous-wave (FMCW) radars at W-band. A shared antenna for transmitter (TX) and receiver (RX) can substantially reduce the form factor, cost, and complexity of radar modules. Due to the simultaneous operation of the TX and RX in FMCW radars, employing a shared antenna will, however, significantly increase TX-to-RX leakage, resulting in RX saturation and desensitization. Our proposed cancellation scheme employs analog feedback to confine the TX leakage right at the RX input port, and thus, relieves the ongoing RX chain from saturation. The proposed single-antenna transceiver (TRX) prototype was fabricated in 65-nm CMOS technology with a die area of 1 mm2. The output power of 2 dBm was achieved for the TX in a frequency range of 80–84 GHz. In addition, a conversion gain and noise figure of 45 and 15 dB was measured for the RX in the presence of the TX signal via a shared antenna port. TX-to-RX isolation of more than 45 dB was achieved in the operating W-band. The chip consumes 108 mW (80.5 mW for the TX and 27.5 mW for the RX) from a 1.2-V supply voltage. Moreover, the functionality of the single-antenna radar operation was verified by connecting the chip to an on -printed circuit board (PCB) $4 \times 8$ patch antenna array with a simulated gain of 15 dBi, implemented on RO3003 Rogers material. Using the single-antenna radar module as a demo system, a $40\times 50$ cm2 rectangular metallic plate was detected at a distance up to 19 m.

High-Resolution Millimeter-Wave Tomography System for Nondestructive Testing of Low-Permittivity Materials

Tomographic microwave imaging is employed as a method of nondestructive testing in a wide range of industrial applications, e.g., for quality control. However, many low-permittivity materials, such as gaseous substances or foam with high air content, do not provide sufficient contrast to the environment to be measured with existing systems. This article introduces a 77-79-GHz high-resolution tomography system that facilitates the characterization of materials with relative permittivity close to one and very small attenuation. Fully integrated frequency-modulated continuous-wave radar transceivers are utilized as sensors to reduce the system cost and complexity significantly. The medium-dependent time-of-flight between different radar sensors is evaluated to reconstruct the permittivity distribution inside an area-under-test. To solve the underdetermined inverse problem, two methods based on the Tikhonov regularization and total variation regularization are implemented. Individual impacts on measurement uncertainty are investigated. Custom-designed horn antennas ensure a sufficient number of signal paths between the sensors. A prototype is built using two synchronized radar modules and a rotary stage to emulate a higher number of sensors. System simulations and measurements are conducted utilizing various low-permittivity foam phantoms. Successful reconstructions of the 2-D permittivity distribution demonstrate the feasibility of this approach.

Continuous In-Bed Monitoring of Vital Signs Using a Multi Radar Setup for Freely Moving Patients

In hospitals, continuous monitoring of vital parameters can provide valuable information about the course of a patient’s illness and allows early warning of emergencies. To enable such monitoring without restricting the patient’s freedom of movement and comfort, a radar system is attached under the mattress which consists of four individual radar modules to cover the entire width of the bed. Using radar, heartbeat and respiration can be measured without contact and through clothing. By processing the raw radar data, the presence of a patient can be determined and movements are categorized into the classes “bed exit”, “bed entry”, and “on bed movement”. Using this information, the vital parameters can be assessed in sections where the patient lies calmly in bed. In the first step, the presence and movement classification is demonstrated using recorded training and test data. Next, the radar was modified to perform vital sign measurements synchronized to a gold standard device. The evaluation of the individual radar modules shows that, regardless of the lying position of the test person, at least one of the radar modules delivers accurate results for continuous monitoring.

Radar Distance Measurement With Viterbi Algorithm to Resolve Phase Ambiguity

In this article, a precise phase-based radar distance measurement system using a Viterbi decoder to resolve phase ambiguity is presented. Relying on the frequency-modulated continuous-wave radar principle, the introduced method evaluates both the frequency and the phase of the intermediate frequency signal, thus achieving absolute distance measurement with high accuracy. To avoid ambiguity in the distance estimates by half the wavelength of the radio frequency signal, which commonly arises due to 2π ambiguity in the measurement of the phase, the proposed Viterbi-based method estimates the most likely sequence of distances between the radar front end and the target. To verify the system concept, measurements using a commercial 77 GHz radar module were carried out, whereby the contour of a predefined surface containing steps in the height profile had to be determined. The experimental results confirm that the Viterbi-based approach is suitable to resolve phase ambiguity since accurate and repeatable distance estimates were obtained.

An In-Situ Assessment of Wood-in-Service Using Microwave Technologies, with a Focus on Assessing Hardwood Power Poles

Simple SummaryBoth termites and decay fungi use wood as a food source. Termites and decay cause major damage and inflict significant costs on human societies around the world. Currently, power pole testing techniques either involve a subjective evaluation, based on the sound that the pole makes when it is hit by a heavy hammer, or observing wood shaving from holes that are drilled into the core of the pole itself. Drilling is destructive and compromises any protection from wood preservative treatments, allowing termites or decay fungi to enter the pole. This project developed a simple, objective measurement technique, which is based on the transmission of very low power microwave energy through the wood. Two versions of the system were developed, and both could easily distinguish between sound hardwood poles and those which were compromised by decay and termite attack, without compromising the pole’s integrity in any way. These will be of enormous benefit to the power utility industry.Wooden power poles and their ongoing inspection represent a significant investment for most electrical power utilities. This study explored the potential for using microwave fields to non-invasively assess the state of hardwood power poles in a field experiment. Two strategies were assessed: 2.4 GHz microwave field transmission through the pole; and mutual coupling between antennae using a 10.525 GHz radar module applied to the surface of the pole. Both systems distinguished between sound hardwood poles and those which were compromised by decay and subterranean termite attack and infestation.

A Hybrid Radar-Camera Respiratory Monitoring System Based on an Impulse-Radio Ultrawideband Radar.

This paper reports a pilot study of a hybrid radar-camera system that simultaneously monitors the respiration of two subjects. A prototype system was built involving a low-cost impulse-radio ultra-wideband (IR-UWB) radar module and an optical and depth-sensing camera module. The system detects subjects using the camera and utilizes the distance information acquired to guide the signal processing of the radar. This structure simplifies subject identification and tracking for the radar system, provides further context to the radar, and facilitates the extraction of respiration information. Experiments under different scenarios were conducted to evaluate the performance of the system at different distances and angles from subjects. The localization procedure has an average accuracy of 0.1 m. The respiration rates extracted from the radar are comparable with the values from the reference wearable sensor, reporting an average error of 0.79 respirations per minute (RPM) with a standard deviation of 0.71 RPM. The results suggest that the respiration signals from subjects could be accurately monitored with the presented framework. It is also feasible to monitor two subjects at the same time in most scenarios. The proposed framework shows promising potential to work as a ubiquitous monitoring system for multiple subjects.

Radar Sensing-Throughput Tradeoff for Radar Assisted Cognitive Radio Enabled Vehicular Ad-Hoc Networks

In cognitive radio enabled vehicular ad-hoc networks (CR-VANETs), the secondary users, i.e., the secondary intelligent vehicles have the ability to perceive the driving environment and use the unoccupied spectrum of primary users for data transmission. In this paper, we consider the radar assisted CR-VANETs, in which the secondary users firstly sense the surroundings using radar modules periodically and Swerling 0, Swerling 2 and Swerling 4 target models are considered respectively. Note that the secondary users access the spectrum of primary users and communicate with their corresponding receivers when no one is detected by the low range radar module. Moreover, we design the joint radar sensing and data transmission frame structure and formulate the radar sensing-throughput tradeoff problem mathematically. It is proved that the formulated tradeoff indeed has the optimal radar sensing time which yields the maximum throughput for the secondary networks. Numerical results and simulations verify that the optimal radar sensing time achieving the maximum throughput for Swerling 0 target model is 0.05 ms when the radius of the radar sensing region is 320 meters, the densities of the primary users and secondary users are λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> = 0.01/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 0.2/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the received radar SNR is 10 dB and the detection probability is 99.9%. For the Swerling 2 and Swerling 4 target models, the optimal radar sensing times achieving the maximum throughput is 0.14 ms and 0.08 ms respectively when the detection probability is 99%.

Dop‐NET: a micro‐Doppler radar data challenge

Radar sensors have a new growing application area of dynamic hand gesture recognition. Traditionally radar systems are considered to be very large, complex and focused on detecting targets at long ranges. With modern electronics and signal processing it is now possible to create small compact RF sensors that can sense subtle movements over short ranges. For such applications, access to comprehensive databases of signatures is critical to enable the effective training of classification algorithms and to provide a common baseline for benchmarking purposes. This Letter introduces the Dop-NET radar micro-Doppler database and data challenge to the radar and machine learning communities. Dop-NET is a database of radar micro-Doppler signatures that are shareable and distributed with the purpose of improving micro-Doppler classification techniques. A continuous wave 24 GHz radar module is used to capture the first contributions to the Dop-NET database and classification results based on discriminating these hand gestures as shown.

Frequency Detector for Radar System Broadband Transmitter Modules

The necessity of determining the current operating frequency in radar system transmission modules is discussed. A frequency detector has been developed and simulated and its main elements designed—a power divider and microstrip filters. The main criteria that filters must meet are identified. Based on the simulation results, a prototype model of the frequency detector was developed and studied in practice.