Two‐tone continuous‐wave Doppler radar based on envelope detection method

A frequency-shift keying (FSK) radar in the 2.45-GHz band is proposed for highly accurate vital-signs detection. The measurement accuracy of the proposed detector for the heartbeat is increased by using the cross-correlation between the phase differences of signals at two frequencies used by the FSK radar, which alternately transmits and receives the signals with different frequencies. Two frequencies—2.45 and 2.5 GHz—are effectively discriminated by using the envelope detection with the frequency control signal of the signal generator in the output waveform of the FSK radar. The phase difference between transmitted and received signals at each frequency is determined after calibrating the I / Q imbalance and direct-current offset using a data-based imbalance compensation algorithm, the Gram–Schmidt procedure, and the Pratt method. The absolute-distance measurement results for a human being show that the vital signs obtained at each frequency using the proposed FSK radar have a cross-correlation. The heartbeat detection results for the proposed FSK radar at a distance of < 2.4 m indicate a reduction in the error rate and an increase in the signal-to-noise ratio compared with those obtained using a single operating frequency.

Section: Vital-signs Detection Using Fsk Radarmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vital-Signs Detector Based on Frequency-Shift Keying Radar

Sim¹,

Park²,

Yang³

2020

“…In addition, high integration and low power consumption of the VCO-based readout circuit are advantageous for implementing a large-scale sensor array [ 6 , 7 ]. Radar sensors that monitor the change of electromagnetic-wave between the transmitted and received signals generated from the VCO remotely measure the distance, velocity, and vital-signs in real time [ 8 , 9 , 10 ]. Various sensors using VCOs require low phase noise characteristics in VCOs [ 11 , 12 , 13 ].…”

Section: Introductionmentioning

confidence: 99%

Switched-Biasing Techniques for CMOS Voltage-Controlled Oscillator

Kang

Moon

Yang

2021

Self Cite

A voltage-controlled oscillator (VCO) is a key component to generate high-speed clock of mixed-mode circuits and local oscillation signals of the frequency conversion in wired and wireless application systems. In particular, the recent evolution of new high-speed wireless systems in the millimeter-wave frequency band calls for the implementation of the VCO with high oscillation frequency and low close-in phase noise. The effect of the flicker noise on the phase noise of the VCO should be minimized because the flicker noise dramatically increases as the deep-submicron complementary metal-oxide-semiconductor (CMOS) process is scaled down, and the flicker corner frequency also increases, up to several MHz, in the up-to-date CMOS process. The flicker noise induced by the current source is a major factor affecting the phase noise of the VCO. Switched-biasing techniques have been proposed to minimize the effect of the flicker noise at the output of the VCO with biasing AC-coupled signals at the current source of the VCO. Reviewing the advantages and disadvantages reported in the previous studies, it is analyzed which topology to implement the switched-biasing technique is advantageous for improving the performance of the CMOS VCOs.

“…The CW radar can be extended to a frequency-shift keying (FSK) radar based on a similar hardware configuration. This can measure an absolute distance in a short range by using the phase differences between the transmitted and received signals obtained by continuously switching between two or more CW signals with different frequencies [ 10 , 11 , 12 ].…”

Section: Introductionmentioning

confidence: 99%

Detrending Technique for Denoising in CW Radar

Lee

Park

Yang

2021

Self Cite

A detrending technique is proposed for continuous-wave (CW) radar to remove the effects of direct current (DC) offset, including DC drift, which is a very slow noise that appears near DC. DC drift is mainly caused by unwanted vibrations (generated by the radar itself, target objects, or surroundings) or characteristic changes in components in the radar owing to internal heating. It reduces the accuracy of the circle fitting method required for I/Q imbalance calibration and DC offset removal. The proposed technique effectively removes DC drift from the time-domain waveform of the baseband signals obtained for a certain time using polynomial fitting. The accuracy improvement in the circle fitting by the proposed technique using a 5.8 GHz CW radar decreases the error in the displacement measurement and increases the signal-to-noise ratio (SNR) in vital signal detection. The measurement results using a 5.8 GHz radar show that the proposed technique using a fifth-order polynomial fitting decreased the displacement error from 1.34 mm to 0.62 mm on average when the target was at a distance of 1 m. For a subject at a distance of 0.8 m, the measured SNR improved by 7.2 dB for respiration and 6.6 dB for heartbeat.