A novel 2.4 GHz passive duplexer with mismatched load impedance and high isolation between transmitting (TX) and receiving (RX) is proposed for integrated sensing and communication (ISAC) ...applications. By adjusting the impedance of a canceling tuner located between the quadrature coupler and the antenna, the load impedance of the coupler is tactfully mismatched, which reflects a portion of the TX power with the desired amplitude and phase to cancel out the TX/RX leakage to achieve a high TX/RX isolation of >56 dB. In the meantime, by leveraging the quadrature nature of the quadrature coupler, the proposed duplexer makes it possible for the transceiver to operate at dual circularly polarized (CP) mode, which is beneficial for the polarization requirement of ISAC. The proposed duplexer is fully characterized and evaluated in the custom-designed communication and radar sensing systems, and the simulation and experimental results demonstrate the feasibility for ISAC applications.
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.
This paper presents PhysioChair which is a novel sensing technique integrated in smart chairs for noninvasive and continuous detection of multiple physiological signatures. A dual-frequency radar ...system is designed and integrated in the PhysioChair, including a 5.8 GHz single-antenna radar for chest movement detection and a 120 GHz miniaturized radar for pulse detection. The dual-frequency multi-radar sensing system is calibrated to ensure systematic synchronization. Besides the conventional vital signs such as respiration, heartbeat and pulse, this paper proposes techniques and approaches to make it possible for the PhysioChair to estimate additional physiological signatures including heart rate variability (HRV), pulse transit time (PTT), pulse wave velocity (PWV), and blood pressure (BP). Experiments have been launched in an office environment with Photoplethysmography (PPG) and digital sphygmomanometer as reference. The experimental results show a great performance of the proposed PhysioChair in detection of weak physiological signatures. Compared to the ground truth, the estimated physiological signatures such as HRV and BP have mean relative errors below 3%, and 6 out of 7 subjects have an over 90% probability of absolute errors less than 5mmHg. The results reveal the possibility for the PhysioChair to be employed outside the clinic, such as applications in the vast internet-of-things (IoT) and in-home health monitoring.
This article presents a novel 5.8-GHz ISM-band dual-circularly polarized (CP) simultaneous transmit and receive (STAR) common-aperture antenna array (CAAA) for integrated sensing and communication ...(ISAC) in Internet of Things (IoT). A new near-field cancellation technique based on differential feeding and geometrical symmetry is proposed for dual-CP to realize high TX/RX isolation. In addition, a high-impedance surface is introduced to further improve the TX/RX isolation. Furthermore, the parasitic patches are added to enhance the gain and isolation bandwidth (BW). The simulation results demonstrate that the proposed CAAA possesses the merits of high isolation (up to 67 dB), wide isolation BW (better than 40 dB for 240 MHz BW), high gains (up to 10/10.5 dB for right-hand CP (RHCP)/left-hand CP (LHCP)), wide 1-dB gain BWs (better than 230/350 MHz BW for RHCP/LHCP), and low-axial ratios (lower than 1.4 dB). The designed CAAAs are fully characterized and the experimental results meet the simulation very well. For the first time, systematic validations for both wireless communication and radar sensing have been thoroughly carried out by integrating the proposed CAAA in the custom-designed full-duplex radio system. The experimental results not only prove the validity of the design methodology but also the feasibility of employing the proposed CAAA for ISAC, which indicates potential applications in IoT era.
Doppler radar uses phase demodulation to extract the target displacement motion contained in the phase of the echo signal. The demodulation performance is vulnerable to the additive Gauss noise. ...Especially when the signal-to-noise ratio (SNR) is extremely low in the scenarios of long-range or subtle displacement motion sensing, it may be impossible to extract the correct phase information. In this article, a phase demodulation method with high robustness against additive noise is proposed for accurate displacement motion reconstruction. Mathematical derivations are performed to analyze the noise effect on phase demodulation, and it shows that the influence of phase noise is much smaller than the additive noise. Based on this finding, the key idea of the proposed method is to transform the additive noise of <inline-formula> <tex-math notation="LaTeX">I</tex-math> </inline-formula>/<inline-formula> <tex-math notation="LaTeX">Q</tex-math> </inline-formula> signals into phase noise. The simulation results validate the noise analysis and verify the high robustness of the proposed method against additive noise. Furthermore, experiments were carried out to evaluate the proposed method under different radial distances and displacement amplitudes. The experimental results show that the proposed method enables accurate motion sensing even in low-SNR scenarios. In our experiments, we observe that the relative root-mean-square error (RRMSE) of the reconstructed displacement motion can be greatly reduced with the proposed method.
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.
Annually, a significant number of premature infants suffer from apnea, which can easily cause a drop in oxygen saturation levels, leading to hypoxia. However, infant cardiopulmonary monitoring using ...conventional methods often necessitates skin contact, and they are not suitable for long-term monitoring. This article introduces a non-contact technique for infant cardiopulmonary monitoring and an adjustable apnea detection algorithm. These are developed using a custom-designed K -band continuous-wave biomedical radar sensor system, which features a DC-coupled adaptive digital tuning function. By using radar technology to detect chest motions without physical contact, it is feasible to extract significant biological information regarding an infant's respiration and heartbeat. The proposed algorithm utilizes an adaptively adjusted threshold and personalized apnea warning time to automatically measure the total number of apneic events and their respective durations. Experiments have been conducted in clinical environment, demonstrating that both the accurate cardiopulmonary signals and the apneas of varying durations can be effectively monitored using this method, which suggest that the proposed technique has potential applications both inside and outside of clinical settings.
In this letter, a novel co-linearly polarized full-duplex antenna-in-package (AiP) with high Tx/Rx isolation and wide decoupled bandwidth is proposed for integrated sensing and communication (ISAC). ...Fan-out wafer-level packaging technology is employed, and the preparation process is discussed in details. To improve Tx/Rx isolation, the current direction of the patch elements is orthogonal to that of the feeding ports. Two identical 1×2 patch antenna arrays are used as Tx and Rx antennas, respectively. To further suppress mutual coupling, a decoupling loop is proposed to enhance Tx/Rx isolation. In addition, a wideband full-duplex AiP with high isolation and wide decoupled bandwidth is also proposed by using the parasitic technique and the proposed decoupling method. Prototypes are fabricated and measured to verify the proposed AiPs. The measurement results demonstrate that the proposed AiP possesses the merits of high Tx/Rx isolation (up to 53 dB), wide isolation bandwidth (up to 9.2%) and low cost, providing a foundation for chip-level applications in ISAC.
As the most important organ of human body, heart has many measures and indicators to assess the cardiac function in clinic. Ventricular systolic time intervals (STIs) are of major relevance in ...providing crucial information regarding cardiovascular state. However, the existing measurement technologies are costly, complicated to operate, and also require contact sensors. Based on the human cardiovascular model and principle of Doppler cardiogram (DCG), the differential DCG (D-DCG) and quadratic D-DCG (QD-DCG) carry the aortic pressure (AP) information by which the STIs can be calculated. A 24-GHz digital dc-tuning Doppler radar sensor (DRS) has been implemented to detect the accurate DCGs. To assess the feasibility of contactless measurement of the STIs by DRS, clinical experiments and evaluations are carried out in the operation theater (OT). The preejection period (PEP) and the left ventricular ejection time (LVET) estimation results reached 95.23% and 93.12% accuracy, respectively, which indicates that the proposed method has great potential to be used for STIs estimation and could be convenient for patient home monitoring.
In this work, we propose a novel radar-based cardiogram detection technique for contactless RR interval estimation. This technique includes linear baseband signal demodulation process and cardiogram ...extraction algorithm to achieve accurate RR interval estimation with anti-respiration interference performance. At the first step of the proposed technique, the modified differential and cross-multiply algorithm (MDACM) is employed to obtain the accurate reconstruction of the phase shift caused by chest-wall motion in Doppler-radar-based vital sign detection. Secondly, continuous wavelet transform (CWT) with Daubechies wavelet is used for cardiogram extraction from recovered chest-wall motion. Then, the characteristic point indicating the R-peak position can be easily found on the extracted cardiogram. In the meanwhile, the RR interval can be computed after the R-peak positioning. With a custom-designed 24GHz Doppler radar, the experimental validation was carried out. The results show that the RR intervals estimation reached 99.4% accuracy with respect to the simultaneously detected ECG signal, which indicates the proposed technique can be used for further contactless heart rate variability (HRV) measurement.
