Guochao Wang

Application of Linear-Frequency-Modulated Continuous-Wave (LFMCW) Radars for Tracking of Vital Signs

This paper focuses on the exploitation of linear-frequency-modulated continuous-wave (LFMCW) radars for noncontact range tracking of vital signs, e.g., respiration. Such short-range system combines hardware simplicity and tracking precision, thus outperforming other remote-sensing approaches in the addressed biomedical scenario. A rigorous mathematical analysis of the operating principle of the LFMCW radar in the context of vital-sign monitoring, which includes the explanation of key aspects for the maintenance of coherence, is detailed. A precise phase-based range-tracking algorithm is also presented. Exhaustive simulations are carried out to confirm the suitability and robustness against clutter, noise, and multiple scatterers of the proposed radar architecture, which is subsequently implemented at the prototype level. Moreover, live data from real experiments associated to a metal plate and breathing subjects are obtained and studied.

A Hybrid Radar-Camera Sensing System With Phase Compensation for Random Body Movement Cancellation in Doppler Vital Sign Detection

This paper presents a Doppler radar vital sign detection system with random body movement cancellation (RBMC) technique based on adaptive phase compensation. An ordinary camera was integrated with the system to measure the subjects random body movement (RBM) that is fed back as phase information to the radar system for RBMC. The linearity of the radar system, which is strictly related to the circuit saturation problem in noncontact vital sign detection, has been thoroughly analyzed and discussed. It shows that larger body movement does not necessarily mean larger radar baseband output. High gain configuration at baseband is required for acceptable SNR in noncontact vital sign detection. The phase compensation at radar RF front-end helps to relieve the high-gain baseband from potential saturation in the presence of large body movement. A simple video processing algorithm was presented to extract the RBM without using any marker. Both theoretical analysis and simulation have been carried out to validate the linearity analysis and the proposed RBMC technique. Two experiments were carried out in the lab environment. One is the phase compensation at RF front end to extract a phantom motion in the presence of another large shaker motion, and the other one is to measure the subject person breathing normally but randomly moving his body back and forth. The experimental results show that the proposed radar system is effective to relieve the linearity burden of the baseband circuit and help compensate the RBM.

Hybrid FMCW-interferometry radar system in the 5.8 GHz ISM band for indoor precise position and motion detection

A hybrid FMCW-interferometry radar sensor is presented. The proposed measurement system incorporates the linear frequency-modulated continuous-wave (FMCW) mode and the continuous wave (CW) interferometry mode. The radar system works in 5.8 GHz ISM band with a bandwidth of 160 MHz. Equipped with a special signal processing method, the hybrid system is capable of detecting absolute distance as well as slow motion. Experiments show that the absolute position detection has an average accuracy of 1.65 cm, and the accuracy of relative motion tracking is better than 2 mm.

Doppler radar vital sign detection with random body movement cancellation based on adaptive phase compensation

This paper presents a Doppler radar sensor system with camera-aided random body movement cancellation (RBMC) techniques for noncontact vital sign detection. The camera measures the subjects random body motion that is provided for the radar system to perform RBMC and extract the uniform vital sign signals of respiration and heartbeat. Three RBMC strategies are proposed: 1) phase compensation at radar RF front-end, 2) phase compensation for baseband complex signals, and 3) movement cancellation for demodulated signals. Both theoretical analysis and radar simulation have been carried out to validate the proposed RBMC techniques. An experiment was carried out to measure a subject person who was breathing normally but randomly moving his body back and forth. The experimental result reveals that the proposed radar system is effective for RBMC.

Isolate the Clutter: Pure and Hybrid Linear-Frequency-Modulated Continuous-Wave (LFMCW) Radars for Indoor Applications

Radars are among the best exponents of radio-frequency (RF)/microwave devices for remote sensing [1], [2]. Long-range radars have demonstrated outstanding potential not only for defense/security environments, such as the detection, location, and tracking of targets, but also on a plurality of civilian scenarios, such as meteorological/weather measurement tasks, imaging of the Earths surface through synthetic aperture radar (SAR) techniques, monitoring of animal migrations, and many others [3]-[7].

Noncontact large-scale displacement tracking: Doppler radar for water level gauging

Doppler radar has been used for small-scale displacement detection, e.g. respiration and heartbeat. The motion amplitude is less than half a carrier wavelength. In this letter, a novel Doppler radar technique is presented for accurate tracking of large-scale displacement of several carrier wavelengths, e.g., the water level variation. The DC-coupled architecture is used to ensure precise measurement of slow motions even with stationary moment. A novel signal processing approach is proposed to increase the demodulation linearity to deal with inconstant signal amplitude, dynamic dc offset and phase ambiguity in large-scale displacement tracking. Experiments have been carried out in the outdoor environment to monitor the relative water level position in a rain barrel when the water was pumped in or drained out. It is shown that the proposed technique can accurately gauge the relative water level variation of 3.5 wavelengths with mm accuracy.

Clutter interference reduction in coherent FMCW radar for weak physiological signal detection

Frequency modulated continuous wave (FMCW) radar is moving from long range detection to indoor short distance target monitoring and has already demonstrated its unique advantages over other approaches. The state-of-the-art coherent FMCW radar, especially, can provide very accurate result in small motion signal detection. However, the performance is sensitive to the clutters that surround the target. In this paper, a clutter reduction technique is developed to further enhance the performance and the robustness of coherent FMCW radar for physiological signal detection. Both theoretical and experimental results are presented to demonstrate the feasibility of the adopted solution.

Bridge Deflection Monitoring Using Small, Low-Cost Radar Sensors

The ability to accurately measure bridge deflections is an important aspect of bridge monitoring and maintenance, both in the US and internationally. Static deck deflections are used to provide load ratings while dynamic deflection measurements may be used to track changes in the dynamic behavior of the bridge due to environmental, loading, and condition changes. Directly measuring bridge deflection has proven challenging, requiring either a fixed reference point or the use of non-contact laser sensors. This presentation introduces wireless, continuous wave radar sensors developed for bridge monitoring applications. The small, bridge-mounted sensors provide a practical and low-cost solution for a range of measurement conditions. As the bridge moves, the radars send a continuous wave that is reflected by a stationary target (either the ground below or a fixed transponder, depending on the application). The reflected signal contains the information necessary to extract the bridge motion. While the theoretical operation is straightforward, there are challenges associated with signal demodulation and data processing in the presence of noise due to interference or long detection ranges. Characterization of the static and dynamic performance of the radar is presented, as well as guidelines for their practical application. The audience of this presentation will be both researchers and practitioners working to improve bridge inspection and monitoring practices. Specifically, the audience will learn about a novel technology to improve bridge testing, gain an understanding of the advantages and challenges of applying radar technology to structural monitoring, and be presented with strategies for achieving a network of distributed radar sensors to capture bridge responses.

Non-contact measurement of rotational movement using miniature Doppler radar

In this paper, the Doppler radar non-contact sensing technology is extended from measurement of one dimensional movement to a practical application in measuring rotational movement. Both simulation and experiment show that Doppler radar can detect the speed of angular movement such as electric fans or motor rotation. It has been shown that in Doppler radar based non-contact rotational movement measurement, the baseband output will have a dominant fundamental frequency that is multiple of the rotation frequency that depends on the structure of reflectors on the target.

Software-configured smart radar sensor for civil and biomedical applications

Software has shown much higher flexibility when compared to hardware so as to be widely used in digital signal processing. In fact, hardware and analog system can also gain merits from the flexibility of software. In this paper, a hybrid radar system is described. Its transmitted signal and operating mode are digitally configured by software, which is different from conventional radar front-end that is mainly decided by hardware. This method helps radar sensors to break through some bottlenecks that traditional radar systems have been long suffering. The limitations of conventional radar for portable civilian applications used to be considered as hardware problems since they are directly related to some physical parameters of radars. In this paper, the presented software-configured radar sensors were tested in civil and biomedical applications, and demonstrates that this method can lead the radar as a mean of wireless sensor to the areas dominated by contact or invasive technology, or can further boost the performance in existing applications.