Fu-Kang Wang

Single-Antenna Doppler Radars Using Self and Mutual Injection Locking for Vital Sign Detection With Random Body Movement Cancellation

This work presents a single-antenna self-injection-locked (SIL) radar to reduce the hardware complexity of continuous-wave (CW) Doppler systems. The theory provides a basis for determining the signal-to-noise spectral density ratio (SNDR) with the effects of clutter. Experimental results agree closely with the theoretical predictions, showing that the clutter does not affect the optimal SNR performance in an SIL radar. A single-antenna SIL radar array is designed to detect vital signs with random body movement cancellation. To this end, a subject is placed between two single-antenna SIL radars to measure the rates of respiration and heartbeat using Doppler shift, and the effects of random movement of the subject are cancelled by wireless mutual injection locking (MIL) of the two radars. In an experiment, a prototype of such a two-radar array with a spacing of 2 m was implemented at 2.4 GHz, providing accurate and reliable cardiopulmonary monitoring of a subject who jogged on a treadmill with random body motion of many centimeters.

A Novel Vital-Sign Sensor Based on a Self-Injection-Locked Oscillator

A novel vital-sign sensor with a self-injection-locked oscillator and a frequency demodulator to reduce system complexity and improve sensitivity is proposed. The theory provides a delta-sigma model to account for the excellent signal-to-noise spectral density ratio in a parametric study of the sensitivity performance. Then, the experiments verify the sensing principle and the predicted performance. Accordingly, a prototype sensor with high sensitivity is realized for noncontact cardiopulmonary monitoring, achieving a long sensing distance without the need for a low-noise amplifier. The sensing distance can grow four times longer by doubling the operating frequency. Furthermore, the sensor using a swept frequency can eliminate the null detection points and the external radio interference. As an experimental result, the sensor, which is placed 4 m away from the subject, can reliably detect the heartbeat signal an the operating frequency of 3.6 GHz and an output power level of 0 dBm.

A Rigorous Analysis of a Phase-Locked Oscillator Under Injection

This study presents injection-pulling effects on a local oscillator (LO) for wireless applications. A discrete-time analysis is provided to predict output spectra of the LO pulled by a sinusoidal and angle-modulated injection signal. A phase-locked loop synthesizer with an injection signal is analyzed in frequency domain to account for the inherent bandpass filtering on the injection signal. In addition, a phase noise model is developed by using the proposed frequency-domain approach to characterize the overall phase noise of a phase-locked oscillator under injection. Comparison between theoretical predictions and experimental results shows excellent agreement.

A Review on Recent Progress of Portable Short-Range Noncontact Microwave Radar Systems

This paper reviews recent progress of portable short-range noncontact microwave radar systems for motion detection, positioning, and imaging applications. With the continuous advancements of modern semiconductor technologies and embedded computing, many functionalities that could only be achieved by bulky radar systems in the past are now integrated into portable devices with integrated circuit chips and printed circuits boards. These portable solutions are able to provide high motion detection sensitivity, excellent signal-to-noise ratio, and satisfactory range detection capability. Assisted by on-board signal processing algorithms, they can play important roles in various areas, such as health and elderly care, veterinary monitoring, human-computer interaction, structural monitoring, indoor tracking, and wind engineering. This paper reviews some system architectures and practical implementations for typical wireless sensing applications. It also discusses potential future developments for the next-generation portable smart radar systems.

An injection-locked detector for concurrent spectrum and vital sign sensing

This paper proposes a concurrent spectrum and vital sign sensor using an injection-locked detector. To achieve this goal, two different sensing mechanisms are involved. One is to employ the injection locking and pulling effects in an oscillator to fast detect the frequency and power of a wireless communication signal. The other is to use a self-injection-locked oscillator to detect Doppler shift for measuring the breathing and heartbeat rate of a target. A prototype system operating in S-band has been implemented to validate the proposed sensor architecture.

Concurrent Vital Sign and Position Sensing of Multiple Individuals Using Self-Injection-Locked Tags and Injection-Locked I/Q Receivers With Arctangent Demodulation

This work presents a wireless system that operates in the 2.4 GHz ISM band for concurrently sensing the vital signs and positions of multiple individuals. Characterized by low complexity and high accuracy, the proposed system consists of two main parts. One is a self-injection-locked (SIL) tag carried by a subject, which emits a sinusoidal frequency-modulated (SFM) signal with vital sign information. The other is a group of injection-locked (IL) I/Q receivers, which performs arctangent demodulation of the SFM signal to obtain the position information without using RF reference signals, and simultaneously extracts the vital sign information of the subject. In the experiment, the system is capable of sensing multiple individuals based on frequency division multiple access (FDMA) technique. Moreover, fidgeting effect on the detection of vital signs has been greatly reduced by a spectral product approach. Accordingly, it is demonstrated that the experimental prototype provides accurate information about the vital signs and positions of different individuals in an indoor environment.

Mutual injection-locked SIL sensor array for vital sign detection with random body movement cancellation

This paper presents a self-injection-locked (SIL) sensor array for cancelling the effects of random body movement on the detection of vital signs. To achieve this goal, a subject is seated between two SIL sensors to measure rates of respiration and heartbeat using the Doppler shift, and the effects of random movements by the subject are cancelled by wireless mutual injection locking (MIL) of the two sensors. In the experiments, a prototype for such a two-sensor array with a spacing of 2 m was implemented at 2.4 GHz, providing accurate and reliable cardiopulmonary monitoring of a subject who exhibited random body motions of several centimeters.

A Novel RF Sensing Circuit Using Injection Locking and Frequency Demodulation for Cognitive Radio Applications

A novel RF sensing circuit for a cognitive radio to sense spectral environment is proposed using injection locking and frequency demodulation techniques. The research starts with deriving a generalized locking equation for oscillators as a theoretical basis, and then develops the sensing principle and circuit architecture to a practical and useful level. To accurately evaluate the sensing performance, a discrete time approach is investigated to compute the sensed output signal. In the experiments, a prototype circuit is designed in the 2.4-GHz industrial-scientific-medical band to cover a sensing frequency range from 2.4 to 2.484 GHz. The spectrum scanning over the 84-MHz bandwidth is accomplished in less than 1 ms. The experimental results agree quite well with the theoretical predictions, showing that the proposed RF sensing circuit can fast and reliably detect frequency and power for analog and digital modulation signals.

Analysis and Improvement of Direct-Conversion Transmitter Pulling Effects in Constant Envelope Modulation Systems

Elucidating how local oscillator (LO) pulling affects a wireless direct-conversion transmitter that uses constant envelope modulation is of concern for global system for mobile communication (GSM). Therefore, this paper presents a phase dynamic model for a phase-locked loop (PLL) under directly modulated self-injection to evaluate the degraded phase noise performance of an LO pulled by a feedback modulation signal from the power amplifier output. Additionally, based on theoretical analysis, the proposed model can instruct system designers on how to optimize PLL parameters, as well as introduce an inner self-injection to minimize the impact of pulling effects. The improved performance is verified by implementing a Gaussian minimum-shift keying transmitter for GSM applications. Furthermore, the theoretical and experimental results correlate well with each other.

Gesture Sensing Using Retransmitted Wireless Communication Signals Based on Doppler Radar Technology

This paper presents a Doppler radar based on an injection-locked quadrature receiver (ILQR) architecture that can use the wireless communication signals from an input cable or an antenna to perform gesture sensing at a short distance. Since the proposed radar does not require an illumination source, radio interference does not occur. To study parametrically the effect of the signal parameters on radar detection performance, a simulation was carried out by modeling the radar system in the discrete-time domain, and the results were verified experimentally using an actuator. In demonstrated applications, the radar uses an input 20 MHz Long-Term Evolution (LTE) signal or captures an ambient Wi-Fi signal to detect several gestures quite successfully.