Frequency-modulated Continuous-wave Mode Research Articles

Contactless and short‐range vital signs detection with doppler radar millimetre‐wave (76–81 GHz) sensing firmware

AbstractVital signs such as heart rate (HR) and respiration rate (RR) are essential physiological parameters that are routinely used to monitor human health and bodily functions. They can be continuously monitored through contact or contactless measurements performed in the home or a hospital. In this study, a contactless Doppler radar W‐band sensing system was used for short‐range, contactless vital sign estimation. Frequency‐modulated continuous wave (FMCW) measurements were performed to reduce the influence of a patient's micromotion. Sensing software was developed that can process the received chirps to filter and extract heartbeat and breathing rhythm signals. The proposed contactless sensing system eliminates the need for the contact electrodes, electric patches, photoelectric sensors, and conductive wires used in typical physiological sensing methods. The system operates at 76–81 GHz in FMCW mode and can detect objects on the basis of changes in frequency and phase. The obtained signals are used to precisely monitor a patient's HR and RR with minimal noise interference. In a laboratory setting, the heartbeats and breathing rhythm signals of healthy young participants were measured, and their HR and RR were estimated through frequency‐ and time‐domain analyses. The experimental results confirmed the feasibility of the proposed W‐band mm‐wave radar for contactless and short‐range continuous detection of human vital signs.

Emulation and Malicious Attacks to Doppler and FMCW Radars for Human Sensing Applications

This article presents emulation and adverse attack scenarios for Doppler radar-based motion sensors and frequency-modulated continuous-wave (FMCW) radars employed for noninvasive vital signs measurement and human presence sensing. In contrast to existing radar threat models, the proposed model is tuned to mimic two characteristics of a human target measured by radars, i.e., the motion artifacts generated by a walking human and the inherent chest motion. Electronically synthesizing the abovementioned characteristics can interfere with the normal operation of radar systems used for automation, bioauthentication, and surveillance applications. The attacking/emulation systems were realized using commercially available radio frequency (RF) components. The 5.8-GHz benchtop prototypes of the Doppler- and FMCW-mode systems were designed, and experiments were conducted to validate the threat of these systems. First, a single-sideband (SSB) mixer is utilized to electronically modulate the continuous-wave (CW) signal transmitted by a Doppler radar to resemble a walking human subject. Next, fake human targets are injected into an FMCW radar by using an analog phase shifter that mimics the vital sign motion of a real human subject. In addition to impersonating the human vital sign motion, the FMCW mode spoofing system has the capability to alter the range of the human target without requiring any synchronization with the victim radar. The FMCW mode spoofing system successfully deceived two state-of-the-art human detection algorithms. Finally, a brief discussion is presented on the feasibility of using the proposed Doppler and FMCW mode spoofing device architecture as respective radar target emulators.

A 24 GHz FMCW/Doppler Dual-Mode Frequency Synthesizer With 68.8 kHz RMS FM Error and 1.25 GHz Chirp Bandwidth

This brief presents a 24 GHz dual-mode frequency synthesizer designed in a 55-nm CMOS technology supporting both Doppler and frequency modulated continuous wave (FMCW) radars. The effects of chirp linearity and delta-sigma modulation (DSM) resolution on the rms FM error is analyzed. A design procedure for the PLL loop bandwidth and time interval of the frequency step to reduce the rms FM error is proposed. A voltage-controlled oscillator (VCO) featuring a four-coil transformer load is developed providing differential local oscillation (LO) signals for the transmitter (TX) and quadrature LO signals for the 2-channel receiver (RX). The prototype is designed with a loop bandwidth of 350 kHz, a frequency step time interval of <inline-formula> <tex-math notation="LaTeX">$2 ~\mu s$ </tex-math></inline-formula>, and a VCO tuning linearity of 26&#x0025;. In the FMCW mode, it achieved an rms FM error of 68.8 kHz over a 1.25 GHz chirp bandwidth. In the Doppler mode, the VCO operates in the free-running mode to save power consumption. An 8-bit digital-to-analog converter (DAC) is used to provide the VCO control voltage compensating process and voltage variations. The free-running VCO operates at a 24.125 GHz and has a frequency error of less than 1 MHz.

G-Band Radar for Humidity and Cloud Remote Sensing

VIPR (vapor in-cloud profiling radar) is a tunable G-band radar designed for humidity and cloud remote sensing. VIPR uses all-solid-state components and operates in a frequency-modulated continuous-wave (FMCW) radar mode, offering a transmit power of 200-300 mW. Its typical chirp bandwidth of 10 MHz over a center-frequency tuning span of 167-174.8 GHz results in a nominal range resolution of 15 m. The radar's measured noise figure over the transmit band is between 7.4 and 10.4 dB, depending on its frequency and hardware configuration, and its calculated antenna gain is 58 dB. These parameters mean that with typical 1 ms chirp times, single-pulse cloud reflectivities as low as -26 dBZ are detectable with unity signal-to-noise at 5 km. Experimentally, radar returns from ice clouds above 10 km in height have been observed from the ground. VIPR's absolute sensitivity was validated using a spherical metal target in the radar antenna's far-field, and a G-band switch has been implemented in an RF calibration loop for periodic recalibration. The radar achieves high sensitivity with thermal noise limited detection both by virtue of its low-noise RF architecture and by using a quasioptical duplexing method that preserves ultrahigh transmit/receive isolation despite operation in an FMCW mode with a single primary antenna shared by the transmitter and receiver.

A 32-GHz Nested-PLL-Based FMCW Modulator With 2.16-GHz Bandwidth in a 65-nm CMOS Process

This article presents a 32-GHz frequency modulated continuous wave (FMCW) modulator based on the phase-locked loop (PLL) with nested sub-PLL structure in a 65-nm CMOS process. With the sub-PLL, the low-pass effect in phase domain is realized, reducing the noise folding effect, quantization noise, and spurs due to the delta sigma modulator (DSM). To achieve good stability and phase noise performance, both the phase-domain model and the phase noise model are analyzed and simulated. Based on these models, the chirp linearity is discussed and simulated, which helps to determine the design parameters and verifies the linearity improvement. The measurement results illustrate that in fractional-N mode, the nested-PLL achieves the phase noise of -91 dBc/Hz at 1-MHz offset frequency and the fractional spurs of less than -54 dBc at 30.78-GHz output frequency. In FMCW mode, the proposed modulator achieves a triangular chirp with 1.08-2.16-GHz bandwidth at about 32-GHz center frequency. In addition, the measured root mean square (rms) frequency errors of 400 and 770 kHz are achieved with the ramp slopes of 1.08 GHz/93 μs and 2.16 GHz/93 μs, respectively. Measurement results prove the improvements of the phase noise and chirp linearity with the sub-PLL. Including all pads, the chip occupies a silicon area of 1.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and consumes 62-mW dc power.

Multiple Range and Vital Sign Detection Based on Single-Conversion Self-Injection-Locked Hybrid Mode Radar With a Novel Frequency Estimation Algorithm

This article presents a single-conversion self-injection-locked (SIL) (SCSIL) hybrid mode radar with a novel frequency estimation algorithm, which improves the range resolution in a frequency-modulated continuous-wave (FMCW) mode and simultaneously detects the vital signs of multiple subjects in the CW mode. The system architecture includes an SIL oscillator (SILO), a frequency converter, two antennas, and a noncoherent frequency demodulator. Due to the frequency–phase relationship in the spectrum of the beat signal in the FMCW mode, the distance to the closely spaced subjects can be determined. Moreover, the algorithm will identify the most dominant component and remove it from the input signal, and the steps are repeated until the residual-to-input energy ratio is less than the threshold value. This iterative method can thus distinguish multiple signals whose frequencies are close to each other and can support a superresolution analysis in both FMCW and CW modes. In an experiment, the radar with a 150-MHz bandwidth and a sensing period of 20 s can simultaneously provide accurate range and vital sign information of two adjacent subjects with radial and azimuth spacings of 60 cm and 5°, respectively.

Fully Integrated Dual-Mode X-Band Radar Transceiver Using Configurable Receiver and Local Oscillator

In this paper, a fully-integrated dual-mode X-band radar transceiver that supports Doppler radar and frequency modulated continuous wave (FMCW) radar is proposed. To remove large off-chip DC-blocking capacitors in the Doppler mode, the double-conversion technique and local oscillator (LO) chopping technique are introduced. These techniques remove the DC offset and makes the transceiver more robust to the TX to RX leakage. In addition, they also improve the noise figure (NF) by filtering out 1/f noise of the analog baseband. The FMCW radar is realized using a direct-conversion receiver and a chirp generator. The chirp generator consists of a frequency sweep generator (FSG) and a fractional-N phase-locked loop (PLL). All the analog baseband components including a programable gain amplifiers (PGA) and 1/R 4 range compensation filters are integrated on the chip as well as a bandgap and low-dropout regulators. The operating frequency is from 9.7 to 12.3 GHz, which consumes 216 mW in Doppler mode and 201.6 mW in FMCW mode from a 1.2-V supply voltage. The maximum chirp bandwidth is 750 MHz and the maximum receiver gain is 76 dB with 6-dB gain step. The chip size of the transceiver is 7.68 mm 2 including all the pads.

Vital-SAR-Imaging With a Drone-Based Hybrid Radar System

Full-coverage synthetic-aperture radar (SAR) imaging and human target identification in complex scenes are very important for security and rescue applications. In this paper, a drone-based vital-SAR-imaging hybrid radar system is proposed to realize targets’ imaging and human identification simultaneously. Carried by an operational custom-built drone with a designed S-shaped trajectory, 2-D SAR images of the entire region could be obtained through the frequency-modulated continuous-wave mode, and the “vital Doppler” effect of human target can be searched through the Doppler mode. Then, the vital-SAR-imaging could be achieved. Several experiments including cart-based SAR imaging with three trajectories, cart-based vital-SAR-imaging, and drone-based multitrajectory vital-SAR-imaging were carried out to reveal the capability and distinct operational features of the proposed system. Experimental results demonstrate that the system has the ability to obtain SAR imaging results in different scenes with multiple trajectories, and the human target could be effectively distinguished from other stationary objects. The results show that the lowest human target location error is 0.06 m in a $4\,\,\text {m} \times 9$ m indoor region, which illustrates the great potential for search and rescue applications.

A Portable FMCW Interferometry Radar With Programmable Low-IF Architecture for Localization, ISAR Imaging, and Vital Sign Tracking

This paper presents a portable radar system for short-range localization, inverse synthetic aperture radar imaging, and vital sign tracking. The proposed sensor incorporates frequency-modulated continuous-wave (FMCW) and interferometry (Doppler) modes, which enable this radar system to obtain both absolute range information and tiny vital signs (i.e., respiration and heartbeat) of human targets. These two different operation modes can be switched through an on-board microcontroller. To simplify the system, the proposed radar utilizes the audio card of a laptop to sample the baseband signal. The FMCW mode of the radar uses operational-amplifier-based circuits to generate an analog sawtooth signal and a reference pulse sequence (RPS). The RPS is locked to the sawtooth signal to obtain coherence for the radar system. For the interferometry mode, a low-intermediate-frequency modulation method is implemented to avoid the slow vital signs from being distorted by the high-pass filter of the audio card. Several experiments were carried out to reveal the capability and distinct operational features of the proposed portable hybrid radar. The experiments also showed that the system can easily detect glass, which is usually difficult to identify for optical-based sensors. In addition, 2-D scanning in a complex environment revealed that the proposed radar was able to differentiate human targets from other objects. Moreover, ISAR images were used to isolate moving human targets from surrounding clutter. Finally, the proposed radar also demonstrated its ability to accurately measure vital signs when a human subject sits still.

A Hybrid FMCW-Interferometry Radar for Indoor Precise Positioning and Versatile Life Activity Monitoring

This paper presents a hybrid radar system that incorporates a linear frequency-modulated continuous-wave (FMCW) mode and an interferometry mode for indoor human localization and life activity monitoring applications. The unique operating principle and signal processing method allow the radar to work at two different modes for different purposes. The FMCW mode is responsible for range detection while the interferometry mode is responsible for life activities (respiration, heart beat, body motion, and gesture) monitoring. Such cooperation is built on each mode's own strength. Beam scanning is employed to determine azimuth information, which enables the system to plot 360° 2-D maps on which the room layout and objects' location can be clearly identified. Additionally, the transmitted chirp signal is coherent in phase, which is very sensitive to physiological motion and allows the proposed technique to distinguish human from nearby stationary clutters even when the human subjects are sitting still. Hence, the proposed radar is able to continuously track the location of individuals and monitor their life activities regardless of the complex indoor environment. A series of experiments have been carried out to demonstrate the proposed versatile life activity monitoring system.

K-Band Dual-Mode Receiver CMOS IC for FMCW/UWB Radar

This brief presents a fully integrated CMOS receiver that is capable of dual-mode frequency-modulated continuous-wave (FMCW) and ultrawideband (UWB) radar operations using the 0.13- $\mu\hbox{m}$ CMOS technology. The circuit consists of a low-noise amplifier, active mixers, an in-phase and quadrature generator, and buffers. In the proposed receiver, not only the gain but also the bandwidth of the overall receiver can be tailored by the switching of the center frequencies of stages and without lowering the quality factor of each stage. As a result, the receiver achieves a conversion gain of 36.7 dB, a 1-dB power gain compression point (P1dB) of $-$ 29.7 dBm, and a double sideband (DSB) noise figure (NF) of 6.1 dB in the narrowband FMCW mode. The receiver also achieves a conversion gain of 27.4 dB with a 3-dB bandwidth of 6.1 GHz, a P1dB of $-$ 21.6 dBm, and a DSB NF of 7.4 dB in the UWB pulse mode. Its performance is comparable with that of previously published chips that only operate in a single mode.

Efficient and precise frequency-modulated continuous wave synthetic aperture radar raw signal simulation approach for extended scenes

Frequency-modulated continuous wave (FMCW) synthetic aperture radar (SAR) system is widely used for earth observation and space detection, where short revisits time at low cost are desirable, or small size is required. Therefore a FMCW SAR raw signal simulator is required to quantitatively support the design of a SAR mission operating in the FMCW mode, to help mission planning, test processing algorithms and analyse jamming and noises. Time-domain SAR raw signal simulation can be easily conceived, but it is extremely time and memory consuming. In this study, an efficient FMCW SAR raw signal simulation approach for extended scene is proposed based on chirp-Z transform (CZT). This is the first time that a FMCW SAR simulator is proposed in the two-dimensional frequency domain. By taking advantage of fast Fourier transform, the proposed approach highly reduces the computational load with respect to the time domain approach. Furthermore, CZT algorithm can accurately simulate the range-variation of the range cell migration term, which guarantees the precision of the proposed approach. Wavenumber domain algorithm is applied to focus the conceived raw signal. Finally, point targets, the electromagnetic imaging and real FMCW image are used to validate the proposed simulation approach.

Towards Three-Dimensional Millimeter-Wave Radar With the Bistatic Fast-Factorized Back-Projection Algorithm—Potential and Limitations

In this paper, we report on a time-domain approach for 3-D synthetic image reconstruction at stand-off distances called the bistatic fast-factorized back-projection (BiFFBP) algorithm. Although the algorithm is suited for multiple purposes, it is applied in this paper to a millimeter-wave radar system that operates in a frequency-modulated continuous-wave mode between 234 and 306 GHz. After initially mapping the bistatic to a quasi-monostatic configuration, the algorithm recursively factorizes both, the aperture positions and the target area. Three-dimensional reconstructions are shown for a simulated point-target in order to evaluate the point-spread-function of the system. In addition, 2-D-imaging is performed on real objects at stand-off distances using a scanner system that consists of 8 transmitters and 16 receivers. Reconstructions with the BiFFBP-algorithm are compared with the global back-projection (GBP) algorithm that serves as a benchmark. The results show that the BiFFBP-approach yields similar results to the GBP with respect to dynamic range in the image and the overall image quality. It is also shown that a resolution of 2 cm can be achieved with relatively few elements, no scanning, and over a large field-of-view.