Linear Frequency Modulated Continuous Wave Radar Research Articles

Detection of Fast-Moving and Accelerating Target Using Linear Frequency-Modulated Continuous-Wave Radars

Detection of Fast-Moving and Accelerating Target Using Linear Frequency-Modulated Continuous-Wave Radars

Characterization of the Frequency Ramp Nonlinearity Impact on the Range Estimation Accuracy and Resolution in LFMCW Radars

The ranging accuracy and range resolution in linear-frequency-modulated continuous-wave (LFMCW) radars are vulnerable to the nonlinearity of the transmitted frequency ramp. The frequency ramp nonlinearity (FRN) leads to the degradation of accuracy in range estimation and deteriorates the range resolution in LFMCW radars, which becomes even worse as the target range increases. The uncertainty of the type of FRN makes the problem more complicated. This paper proposes a new range-dependent resolution model and a new range-dependent accuracy model based on the theoretical analysis and experimental evaluations, which characterizes the impact of different types of FRN on the range resolution and accuracy in LFMCW radars. The proposed models have established the quantitative relationship between the FRN, the target distance, and the range accuracy and resolution. A nonlinearity index is utilized in the analysis to quantify the extent of FRN. Moreover, a novel design methodology is also proposed which may guide the design of LFMCW radars under the influence of FRN. Four typical types of FRN that are reasonable in practical LFMCW radars are taken into consideration in both simulations and experiments to validate the proposed theory and methodology.

Accurate Measurement of Human Vital Signs With Linear FMCW Radars Under Proximity Stationary Clutters.

Vital sign detection using linear frequency-modulated continuous-wave (LFMCW) radar may be subject to the proximity stationary clutters. This paper presents a novel technique to synthesize the slow-time I/Q signals, which are equivalent to those in a single tone quadrature CW radar, from a single-channel LFMCW radar. It correlates the two types of radars in such a way that the proximity stationary clutters are translated to direct current (DC) offsets in the synthesized I/Q signals across slow-time. The circle-fitting based DC offsets calibration (DCcal) technique, which was developed for CW radar, can now be applied to eliminate the impact of the proximity stationary clutters in LFMCW radars for accurate vital sign detection. Moreover, the modified differentiate and cross-multiply (MDACM) algorithm can also be leveraged to eliminate the phase ambiguity issue. Thorough theoretical analysis and working principles are presented. Simulations are performed to validate the proposed technique. Moreover, exhaustive experiments are carried out with a millimeter-wave 79 GHz FMCW radar in the office environment. Mechanical vibration and vital signs are extracted with micrometer-level accuracy in the existence of proximity stationary clutters.

Adaptive digital self-interference cancellation based on fractional order LMS in LFMCW radar

Adaptive digital self-interference cancellation (ADSIC) is a significant method to suppress self-interference and improve the performance of the linear frequency modulated continuous wave (LFMCW) radar. Due to efficient implementation structure, the conventional method based on least mean square (LMS) is widely used, but its performance is not sufficient for LFMCW radar. To achieve a better self-interference cancellation (SIC) result and more optimal radar performance, we present an ADSIC method based on fractional order LMS (FOLMS), which utilizes the multi-path cancellation structure and adaptively updates the weight coefficients of the cancellation system. First, we derive the iterative expression of the weight coefficients by using the fractional order derivative and short-term memory principle. Then, to solve the problem that it is difficult to select the parameters of the proposed method due to the non-stationary characteristics of radar transmitted signals, we construct the performance evaluation model of LFMCW radar, and analyze the relationship between the mean square deviation and the parameters of FOLMS. Finally, the theoretical analysis and simulation results show that the proposed method has a better SIC performance than the conventional methods.

Theory and method of multi-point synchronous deformation and vibration measurement based on millimeter-wave sensing

Although accelerometer-, vision-, and laser-based sensing technologies are widely used in deformation and vibration measurements, the multi-point simultaneous deformation and vibration measurement of large-scale structures with high accuracy remains a challenge. Herein, we developed a novel technology for contactless deformation and vibration measurement using millimeter-wave (mmWave) linear frequency-modulated continuous wave radar, establishing the theory and method for multi-point simultaneous deformation and vibration measurement based on mmWave sensing. The principle of mmWave multi-point vibration measurement and a method of displacement extraction were systematically described using the baseband signal model of multi-target perception. We built a prototype of the proposed mmWave vibration measurement system and a platform for simulated vibration tests. The accuracy of the mmWave multi-point vibration measurement technology was verified and compared with that of laser displacement sensors. Using the prototype system, we conducted experiments on the multi-point synchronous vibration measurement and model identification of the slender hinged flexible rod structure of a certain aerospace equipment in China and then described the dynamic response monitoring of a large bridge structure. Results showed that the deformation and vibration measurement method based on mmWave sensing developed in this work could conveniently and accurately extract the time domain information of multi-target vibration displacements. Our work provides an innovative method and approach for non-contact multi-point synchronous deformation and vibration measurements that could be applied to the mechanical performance test and health monitoring of large structures.

A Non-Contact Vital Signs Detection in a Multi-Channel 77GHz LFMCW Radar System

The technology of vital signs detection has been proven of great use, whereas it is still limited by several challenges. One of the major challenges is the random body movements (RBMs), which significantly degrade the accuracy of the measurement. In this paper, a multi-channel 77GHz linear frequency modulated continuous-wave (LFMCW) radar system is investigated to perform vital signs monitoring on multiple targets with the mitigation of RBMs and a novel vital signs detection scheme is provided for the accurate estimates of the respiration rate (RR) and heart rate (HR). In the proposed scheme, a multi-channel Kalman smoother is firstly proposed to address the outliers in the extracted phase histories from the echoes in the multiple receivers, so that enhanced outlier-robust phase histories are acquired for the subsequent estimates of the RR and HR. Furthermore, a novel regional hidden Markov model is then proposed to carry out accurate estimates of RR and HR by exploiting the underlying slowly-varying characteristics of these vital signs for further mitigation of the effects of RBMs. Experimental results demonstrate that the estimated errors in the proposed scheme are less than 2 beats per minute (bpm) for both RR and HR under normal scenarios with young men in the RBMs environment.

An Elaborated Signal Model for Simultaneous Range and Vector Velocity Estimation in FMCW Radar.

A rigorous mathematical description of the signal reflected from a moving object for radar monitoring tasks using linear frequency modulated continuous wave (LFMCW) microwave radars is proposed. The mathematical model is based on the quasi-relativistic vector transformation of coordinates and Lorentz time. The spatio-temporal structure of the echo signal was obtained taking into account the transverse component of the radar target speed, which made it possible to expand the boundaries of the range of measuring the range and speed of vehicles using LFMCW radars. An algorithm for the simultaneous estimation of the range, radial and transverse components of the velocity vector of an object from the observation data of the time series during one frame of the probing signal is proposed. For an automobile 77 GHz microwave LFMCW radar, a computer experiment was carried out to measure the range and velocity vector of a radar target using the developed mathematical model of the echo signal and an algorithm for estimating the motion parameters. The boundaries of the range for measuring the range and speed of the target are determined. The results of the performed computer experiment are in good agreement with the results of theoretical analysis.

One-Bit LFMCW Radar: Spectrum Analysis and Target Detection

One-bit radar, performing signal sampling and quantization by a 1-bit analog-to-digital converter, is a promising technology for many civilian applications due to its low-cost and low-power consumptions. In this article, problems encountered by a 1-bit linear-frequency-modulated continuous-wave (LFMCW) radar are studied, and a two-stage target detection method termed as the dimension-reduced generalized approximate message passing (DR-GAMP) approach is proposed. First, the spectrum of 1-bit quantized signals in a scenario with multiple targets is analyzed. It is indicated that high-order harmonics may result in false alarms and cannot be neglected. Second, based on the spectrum analysis, the DR-GAMP approach is proposed to carry out target detection. Specifically, linear preprocessing methods and target predetection are first adopted to perform the dimension reduction, and then, the generalized approximate message passing algorithm is utilized to suppress high-order harmonics and recover true targets. Finally, numerical simulations are conducted to evaluate the performance of the 1-bit LFMCW radar under typical parameters. It is shown that compared to the conventional radar applying linear processing methods, the 1-bit LFMCW radar has about 1.3-dB performance gain when the input signal-to-noise ratios of targets are low. In the presence of a strong target, it has about 1.0-dB performance loss.

Research on LFMCW Radar Velocity Ranging Optimization System Based on FPGA

Abstract Linear frequency modulation continuous wave (LFMCW) radar is widely used in the field of velocity measurement and ranging because of its high precision and good range resolution. The traditional LFMCW radar uses a single core FFT to do data processing, which is not very fast. This article utilize that advantages of fast and high degree of integration of FPGA, and propose a double-core FFT processor based on the use of the optimized CORDIC parallel algorithm to improve data processing speed, enhance real time, design and realize the calculation module of the double-core FFT data processing module and the distance measuring speed, and finishes the design of the LFMCW radar speed measuring and measuring system with real time and quick advantages. The experimental results show that the system has the characteristics of fast data processing and high reliability, and can measure the moving vehicle in real time and effectively.

A Non-Linear Correction Method for Terahertz LFMCW Radar

The nonlinearity in terahertz (THz) linear frequency modulated continuous wave (LFMCW) radar usually blurs the range profile and decreases the signal to noise ratio, hampering applications where high range-resolution is particularly emphasized. A software correction method, which comprises of transmitted nonlinearity estimation and nonlinear phase compensation for the beat signal, is proposed in this paper to drastically reduce the nonlinearity in THz LFMCW radar. Besides the commonly considered nonlinearity caused by voltage-controlled oscillator (VCO), the nonlinearity from other broadband hardware devices have also been included in our modified correction model, which gives the advantage of preciser compensation. Moreover, utilizing the phase gradient autofocus (PGA) method to estimate the transmitted nonlinear term and the residual video phase (RVP) removal method to remove the range dependency of the received nonlinearity, our method can uniformly compensate the nonlinearity in the whole range profile. In addition, no presupposed parametric model for the nonlinearity waveform is needed, which further strengthens the effectiveness of the proposed method in practical use. Both the simulated data and the real tested data, acquired by a 190 GHz radar with 60 GHz bandwidth, has been used to demonstrate the validity and the effectiveness of the method.

Ground clutter simulation for airborne forward‐looking multi‐channel LFMCW radar

Ground clutter is a crucial factor that affects the detection performance of the airborne forward-looking multi-channel linear frequency modulated continuous wave (LFMCW) radar, so the distribution characteristics of studying the ground clutter plays an important role in suppressing ground clutter and improving radar detection performance. In this article, the authors first use the Ward model to divide the effective clutter area into multiple independent clutter patches and calculate the echo signal of each clutter patch. Then the beat signal of each clutter patch is obtained by the de-chirp processing. Next, a Fourier transform is performed on the beat signal of each clutter patch to determine the range ring where the echo of the clutter patch is located, and the peak spectrum signal of the beat signal of the clutter patch in the same range ring is superimposed, thus the authors can realise the simulation of the ground clutter signal. Finally, the simulation results indicate the effectiveness of the proposed method.

Design and implementation of LFMCW radar system based on ZYNQ

Linear frequency modulated continuous wave (LFMCW) radar has been applied to the field about short-range target detection. In this article, in order to achieve the low cost and general short-range target detection, a semi-physical LFMCW radar system is designed to estimate the distance and speed of the moving target in real scenarios. Meanwhile, the received echo signal is processed by using sparse Fourier transform and fast Fourier transform so as to further improve computational efficiency. Experimental results confirm the effectiveness of the designed semi-physical LFMCW radar system. More importantly, the designed system also lays the foundation for the future engineering application for the LFMCW radar.

Detection of Targets with Small Apparent Doppler Frequencies in LFMCW Radars

Linear Frequency Modulated Continuous Wave (LFMCW) radars are widely used in automotive applications or borders protection because of their noticeable performance. These radars should include Moving Target Indicator (MTI) to suppress all fixed targets in urban crowded areas or open borders. MTI attenuates signals with small apparent Doppler frequencies coming from slowly moving targets, high speedy targets, or those moving with an angle near 90 or -90 degrees to the radar radial direction. In this paper, the frequency response of the MTI is modified by adding a Single Delay Line Integrator (SDLI) following it to enhance its gain for small Doppler frequencies with some degradation in detecting middle Doppler targets. A choice between the traditional structure and the proposed one through a maximum-of criterion is proposed to achieve an improved equal detection performance for all Doppler frequencies. The detection superiority of the proposed method for slowly moving or high speed targets detection over the traditional one is validated for different target scenarios through the Receiver Operating Characteristic (ROC). Implementation considerations for single delay line integrator such as complexity and stability are discussed. A suggested scheme is proposed to achieve complexity reduction as well as stable operation.

Photonic Deramp Receiver for Dual-Band LFM-CW Radar

A photonic deramp receiver based on a photonic mixer for dual-band linear frequency-modulated continuous wave radar is proposed. In the receiver, a novel modulation scheme is developed, employing a dual polarization quadrature phase shift keying modulator which contains four sub-Mach-Zehnder modulators (sub-MZMs). The echoes and reference signal of the first band are modulated to light waves on a pair of peak-biased sub-MZMs for tracking, while the echoes and reference signal of the second band are modulated on the other pair of null-biased sub-MZMs for imaging. An experimental system, operating in C-band and Ku-band with a bandwidth of 850 and 3600 MHz, respectively, is demonstrated and evaluated via a series of inverse synthetic aperture radar imaging tests. The results verify the idea of the dual-band radar receiver, which provides a solution for receiving dual-band echo signals with a single hardware platform.

On fundamental operating principles and range-doppler estimation in monolithic frequency-modulated continuous-wave radar sensors

The diverse application areas of emerging monolithic noncontact radar sensors that are able to measure object?s distance and velocity is expected to grow in the near future to scales that are now nearly inconceivable. A classical concept of frequency-modulated continuous-wave (FMCW) radar, tailored to operate in the millimeter-wave (mm-wave) band, is well-suited to be implemented in the baseline CMOS or BiCMOS process technologies. High volume production could radically cut the cost and decrease the form factor of such sensing devices thus enabling their omnipresence in virtually every field. This introductory paper explains the key concepts of mm-wave sensing starting from a chirp as an essential signal in linear FMCW radars. It further sketches the fundamental operating principles and block structure of contemporary fully integrated homodyne FMCW radars. Crucial radar parameters like the maximum unambiguously measurable distance and speed, as well as range and velocity resolutions are specified and derived. The importance of both beat tones in the intermediate frequency (IF) signal and the phase in resolving small spatial perturbations and obtaining the 2-D range-Doppler plot is pointed out. Radar system-level trade-offs and chirp/frame design strategies are explained. Finally, the nonideal and second-order effects are commented and the examples of practical FMCW transmitter and receiver implementations are summarized.

High‐precision estimation of target range, radial velocity, and azimuth in mechanical scanning LFMCW radar

This study investigates the effects of antenna rotation on range, radial velocity, and azimuth estimation during coherent integration in linear frequency-modulated continuous wave (LFMCW) radars. When antenna scans during the coherent integration time, theoretical analysis indicates that the angle sensing with the traditional sum-difference amplitude-comparison (SDAC) monopulse method and the range, radial velocity estimation with interpolation method are different from that in staring mode. Simulation demonstrates that the estimation performance is heavily impaired by the antenna rotation. In this study, a generalised mathematical model of coherent integration for LFMCW radar is established. Furthermore, a high-precision estimation method, which consists of generalised SDAC monopulse method, radial velocity estimator with modified interpolation curves, and range estimator refined by Doppler frequency, is proposed. A complete signal-processing scheme is proposed for the accurate estimation of the target parameter in mechanical scanning LFMCW radar. A sub-optimal method is provided for practical implementation. Experimental and simulation results show that the proposed method achieves high accuracy and robustness.

Dual-band dechirping LFMCW radar receiver with high image rejection using microwave photonic I/Q mixer.

In this paper, a photonics-based dual-band linear frequency-modulated continuous wave (LFMCW) radar receiver is proposed. The system core is a microwave photonic in-phase and quadrature (I/Q) mixer, whose inherent large bandwidth, high I/Q balance and favorable uniformity enable the receiver to operate over an extremely wide frequency range. An integrated dual-band waveform offers the possibility of independent detection, allowing the sharing of hardware resources and joint dechirp processing of dual bands. In the proof-of-concept experiment, the distance measurements of S- and C-bands are implemented, with a high and uniform image rejection exceeding 28 and 30 dB, respectively. The image rejections of the two bands can be further improved to 43 and 41 dB at least by digital signal processing (DSP). The proposed photonic-assisted receiver is thus able to simplify the architecture and improve performance for the multispectral sensing application.

A phase match based frequency estimation method for sinusoidal signals.

Accurate frequency estimation affects the ranging precision of linear frequency modulated continuous wave (LFMCW) radars significantly. To improve the ranging precision of LFMCW radars, a phase match based frequency estimation method is proposed. To obtain frequency estimation, linear prediction property, autocorrelation, and cross correlation of sinusoidal signals are utilized. The analysis of computational complex shows that the computational load of the proposed method is smaller than those of two-stage autocorrelation (TSA) and maximum likelihood. Simulations and field experiments are performed to validate the proposed method, and the results demonstrate the proposed method has better performance in terms of frequency estimation precision than methods of Pisarenko harmonic decomposition, modified covariance, and TSA, which contribute to improving the precision of LFMCW radars effectively.

Mitigation of stationary clutter in vital‐sign‐monitoring linear‐frequency‐modulated continuous‐wave radars

Stationary clutter can seriously degrade the performance of radar sensors. In the specific context of vital-sign monitoring, this deterioration can lead to the impossibility of tracking the desired motions. Pure linear-frequency-modulated continuous-wave (LFMCW) radars have arisen as an interesting solution to monitor vital signs, featuring both an increased phase-based range precision and an advantageous range-isolation capability. In this study, the impact of clutter on healthcare LFMCW radars is mathematically analysed and a Doppler high-pass filtering technique is proposed for its suppression. Simulation results are provided to highlight the key aspects of the derived mathematical framework and associated Doppler processing. Real experiments are also conducted to prove the validity of the devised clutter-mitigation procedure.

Airport Runway FOD Detection from LFMCW Radar and Image Data

Airport runway Foreign Object Debris (FOD) jeopardizes flight safety and leads to a large amount of financial cost on flight maintenance constantly. Several FOD detection systems based on a variety of detection techniques and architectures have been developed. This paper gives a brief introduction of our FOD detection system, in comparison with FOD detection systems currently in the international market. What distinguish our system from all the others is that, our detection approach is based on both linear frequency modulated continuous wave (LFMCW) radar signal and image data. This innovation combines the advantages of radar in shape detection and image in appearance detection. As a result, it increases the FOD detection rate and reduces the false alarming rate. Experiments following Federal Aviation Administration (FAA) advisory indicate that our system has reached the FAA requirements.