A novel 4-D gesture sensing technique using reconfigurable virtual array method with a 60-GHz frequency-modulated continuous wave (FMCW) radar is presented. The 4-D sensing includes the 3-D spatial ...positioning and the 1-D motion tracking, which combines detection in both spatial and temporal domains. The proposed technique can be used for gesture sensing for both macro gestures such as handwriting letters and numbers, hand drawing different patterns in space and micro gestures such as the fingers' actions of virtual slider, finger tap, and finger wave. Moreover, this work presents a method to reconfigure the working modes of different transmitting and receiving channels in the multiple input and multiple output (MIMO) architecture, which effectively increases the sensing range of the radar sensor and the signal-to-noise ratio (SNR) of the beat signal. For various gestures at different distances or in different environments, the proposed technique can adaptively achieve the best detection by reconstructing the virtual array of the MIMO radar. A series of experiments are carried out in both microwave anechoic chamber and office environments to validate the proposed technique. The experimental results show that the proposed technique performs well in sensing a variety of both macro gestures andmillimeter-level micro gestures. Compared with the conventional MIMO method, the proposed technique increases the sensing range by 3.5 times, and the SNR is also greatly improved by 12 dB when the radar performs gesture sensing at the distance of 0.65 m.
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 subject's 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.
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.
In this article, a novel technique combining asynchronous bandpass sampling and an optimized phase extraction technique (PET) is proposed to demodulate single-channel intermediate frequency (IF) ...signals for displacement motion detection in a dual-phase-locked-loop (PLL) single-sideband (SSB) low-IF radar. The proposed technique leverages the SSB low-IF radar to enable single-channel demodulation of IF signal, thereby preventing any demodulation performance degradation resulting from I/Q channel imbalances. Additionally, asynchronous bandpass sampling is employed to achieve spectral shifting of the IF signal based on a suitable sampling rate interval, consequently reducing the sampling rate and the volume of data. An optimized PET utilizing a sliding window and Fourier transform is introduced to demodulate single-channel IF signals, which offers a higher theoretical maximum unambiguous velocity compared to the conventional PET. Furthermore, compared to the commonly used digital downconversion (DDC) technique, the proposed technique has higher accuracy of the recovered motion trajectory, whose signal-to-noise ratio (SNR) is proven to be approximately 7 dB higher in both theory and experiments under a certain window length. Finally, comprehensive experiments on detecting low and high-speed actuator motion, as well as physiological monitoring, were implemented to demonstrate the advantages of the proposed technique in terms of detection accuracy, SNR, maximum unambiguous velocity, and effectiveness of vital signs detection.
This article presents a framework for frequency modulated continuous wave (FMCW) multiple input multiple output (MIMO) radar vital sign monitoring to achieve accurate heart rate (HR) in home ...application scenarios and low SNR environments. The framework consists of two main parts. The first part includes a 4-D cardiac beamformer, which is a beamformer composed of the distance dimension, azimuth and zenith angles, and the time-frequency dimension. A novel time-domain FMCW radar interference-resistant (IR) phase extraction method is proposed and combined with a spectrum-based cardiac signal quality evaluation model, ultimately focusing the radar array beams on the position of the human heart. The second part involves a modified adaptive HR trace carving technique. This technique involves the analysis of the time-frequency domain vital sign signal, utilizing forward accumulation and backward propagation to reconstruct faint heartbeat trajectory information concealed beneath respiratory harmonics and noise. To validate the proposed framework, a K-band 2T4R FMCW MIMO radar prototype was designed and fabricated. In a total of 20 overnight sleep experiments, the overall RMSE of respiratory rate and HR estimation obtained by the radar prototype based on the proposed framework were 0.53 and 2.68 bpm, respectively. The proposed framework demonstrates robust IR and the capability to operate in extremely low SNR conditions, which holds significant potential in long-term vital sign monitoring applications.
The interferometric radar sensor is superior in detecting the relative displacement motions. The conventional motion-recovery techniques leverage the quadrature <inline-formula> <tex-math ...notation="LaTeX">I/Q </tex-math></inline-formula> signals to reconstruct the phase information, where accurate calibration of the <inline-formula> <tex-math notation="LaTeX">I/Q </tex-math></inline-formula> signals is a prerequisite. Accurate phase demodulation depends on the precision of signals calibration. Incorrect signals calibration and hardware imperfections may lead to false phase demodulation. In this letter, based on the signal segmentation and Hilbert transformation principle, a novel linear phase reconstruction technique is proposed, which not only involves a single receiver channel without bothering the <inline-formula> <tex-math notation="LaTeX">I/Q </tex-math></inline-formula> signals but also gets rid of the <inline-formula> <tex-math notation="LaTeX">I/Q </tex-math></inline-formula> signals calibration. Both simulation and experimental results show that the proposed single channel based phase demodulation (ScD) technique recreates the target motion without any phase ambiguity and improves the accuracy with an root mean squared error (RMSE) less than 0.01 mm, which is over 9 times than that of the other state-of-the-art approaches.
The frequency-modulated continuous-wave (FMCW) radar sensor is subject to phase ambiguity in measuring large displacement of over half a wavelength, which is particularly severe in the ...millimeter-wave FMCW radar sensor due to its short wavelength. The state-of-the-art linear phase demodulation techniques were mostly developed for single tone quadrature continuous-wave (CW) radars such as the Modified differentiate and cross-multiply (MDACM) algorithm. This paper presents a novel linear interferometric displacement measurement technique which can synthesize the quadrature <inline-formula> <tex-math notation="LaTeX">{I}/{Q} </tex-math></inline-formula> signals across slow time from a single-channel FMCW radar. In this way, the linear phase demodulation technique developed for the CW radar can now be leveraged for the FMCW radar. The theoretical analysis and working principles are discussed. Exhaustive experiments are performed to validate the proposed technique. It is demonstrated that the displacement motions as large as 10 times of the wavelength can be precisely extracted from a single channel FMCW radar with micrometer accuracy and without any phase ambiguity.
Signal distortion may happen in conventional accoupled interferometric radar when measuring slow target movements. Existing solutions to preserve signal integrity add to hardware complexity and are ...at extra cost. In this paper, a digital post-distortion (DPD) technique is proposed to compensate the signal distortion in baseband digital domain. For the first time, at no extra hardware cost, an ac-coupled interferometric radar can be used to measure slow movements without losing any signal information-even those with stationary moment. The DPD technique is realized by applying a compensation function, which is the inverse of the baseband system response and obtained in hardware calibration, to the digitized baseband I/Q signals. Both simulation and experimental results show that the proposed technique is robust to recover distorted signals.
The conventional short-range interferometric radar sensors usually employ two separate transmitting (TX) and receiving (RX) antennas for improved TX-RX isolation. However, they are subject to ...increased system size and misalignment of the TX/RX radiation patterns. In this article, a portable 5.8 GHz dual circularly polarized (CP) interferometric radar sensor is presented, which leverages the proposed dual CP common-aperture antenna that reduces the size of the entire radar system. The common-aperture nature gets rid of the radiation pattern misalignment and ensures that the object can be in the optimal boresight direction. Cross polarization, i.e., right-hand CP (RHCP) for TX and left-hand CP (LHCP) for RX or vice versa, was employed based on the sequentially rotated array (SRA), which not only improves the TX-RX isolation but also adapts with the polarization change in radar sensing. Moreover, a near-field cancellation technique was proposed to further increase the TX-RX isolation in the small form factor. A portable 5.8 GHz radar sensor integrated with the proposed dual CP antenna was custom-designed. Compared to the conventional two-antenna architecture, the proposed radar sensor is reduced in size by 140% but can still achieve a high TX-RX isolation of >60 dB at 5.8 GHz. Experiments were carried and the results illustrate that the proposed radar sensor has high micrometer accuracy in detecting the predefined displacement motions and is able to precisely track the human vital signs in the office environment.
Frequency-modulated continuous-wave (FMCW) radar is commonly employed for target detection. Nevertheless, leakage often occurs between the transmitter (Tx) and the receiver (Rx), leading to degrade ...the detection of targets in short range. It happens because the Tx-Rx leakage introduces a time delay that is comparable with that of the backscattered reflections from the target, which worsens the signal-to-noise ratio (SNR) and the signal-to-interference ratio (SIR). This article proposes a novel and versatile time-frequency characteristic-based leakage cancellation technique (TFCBLC). By cleverly exploiting the frequency-domain features of the intermediate frequency (IF) signal, the leakage is mitigated through the IF compensation with an antileakage signal. Moreover, the multichirps convolution technique (MCCT) based on the equivalent FMCW radar has been developed to address the problems associated with challenging detection caused by residual leakage and inherent noise. The proposed technique effectively suppresses the Tx-Rx leakage and attenuates noise, enhancing the system's ability for short-range target detection. A series of simulations and experiments were conducted to demonstrate the effectiveness of the proposed technique for short-range detection with strong leakage and significant noise environments. The results indicate that the SIR and SNR have been improved by around 30 and 17 dB, respectively.
