Detrending Technique for Denoising in CW Radar

Abstract

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.

Radar-Based Monitoring of Vital Signs: A Tutorial Overview

“…To overcome this limitation, a DC coupled radar system has been proposed in [68]. Other techniques have been proposed in [70], [69], and [67] and are based on polynomial fitting and on an LS approach.…”

“…The last formula and (64) lead to the conclusion that a larger bandwidth leads to a better granularity in range estimation, i.e., results in a better range resolution (see also Section VI-A). 2) Some methods, similar to the ones described above for CW Doppler radars, are available for the compensation of a DC offset or of large movements; in fact, they are based on filtering techniques or on polynomial fitting [21], [67], [69]. 3) If the distance between the chest wall and the radar is known with a certain accuracy (e.g., when the radar is employed for monitoring the vital signs of a patient in a bed), a procedure for reducing the region of interest (ROI) can be implemented to simplify the estimation of l. In particular, l can be searched in the ordered set {lm, lm + 1, .…”

“…8(b); the overall number of VAs forming this array is NV = 16, whereas the distance between adjacent virtual elements is d = λ/4. Our data have been processed by the deterministic algorithm illustrated in Section V-B; N ′ 0 = 2 and NA = 4 have been selected in the computation of the 2D-FFT output Xn (69). The range-azimuth map J[0] generated based on the measurements acquired through the MIMO radar in the first chirp interval is represented in Fig.…”

Radar-based Monitoring of Vital Signs: A Tutorial Overview

“…a) The contribution of DC offset and strong low frequency components to the received signal phase can be mitigated by exploiting the method illustrated in [47] and based on polynomial fitting. This method allows to capture the slow temporal variations of that phase and to subtract them from it.…”

“…is the bin-to-meters conversion factor. b) Some methods, similar to the ones described above for CW Doppler radars, are available for the compensation of a DC offset or of large movements; in fact, they are based on filtering techniques or on polynomial fitting [17,47,51].…”