Quadrature Imbalance Compensation With Ellipse-Fitting Methods for Microwave Radar Physiological Sensing

Abstract

Accurate displacement measurement using quadrature Doppler radar requires amplitudes and phase imbalance compensation. Previously, this imbalance calibration has required cumbersome hardware modifications and thus can only be performed in a laboratory setting. Recently, a data-based method that does not require hardware modifications has been proposed. This simplifies the calibration process and allows the calibration to be performed on-site periodically. The method is called ellipse fitting. In this paper, the different factors affecting imbalance estimation accuracy, namely, arc length, initial phase angle, and noise level were thoroughly investigated. The Levenberg-Marquardt (LM) algorithm is proposed for the first time to increase the estimation accuracy as compared to the previously suggested algebraic fitting. Comprehensive simulations and experimental data show that the algebraic fitting method results in biased estimates. The proposed LM method has also been demonstrated to be more robust to noise, varying arc lengths, and different initial angles. The LM method reaches sufficient imbalance estimation accuracy with an arc length of 40% and a noise level of 1.5%.

A 24 GHz Waveguide based Radar System using an Advanced Algorithm for I/Q Offset Cancelation

“…Several subsequent optional calibration steps minimize the remaining absolute measurement error, e.g., by applying ellipse fitting algorithms (Singh et al, 2013;Zakrzewski et al, 2014;Linz et al, 2014) or polynomial approximation based error correction (Will et al, 2017a;Vinci et al, 2011;AOlopade and Helaoui, 2014), or by utilizing a look-up table (Vinci et al, 2011). Thus, the importance of repeatability as a figure of merit increases, which is typically analyzed by evaluating the standard deviation at each calibration point.…”

“…An orthogonalization of the elliptical shape had been investigated in preliminary experiments which yield best results by minimizing the I/Q offset. Furthermore, several algorithms for estimating and reconstructing elliptic I/Q representations have already been published (Singh et al, 2013;Zakrzewski et al, 2014;Linz et al, 2014).…”

Novel Approach for Vibration Detection Using Indented Radar

“…For an Indented Radar setup, these techniques will become error prone because of mismatches such as amplitude, DC and phase imbalances. Even though there are many ellipse based fitting techniques to compensate for mismatch errors but most of these calibrations is a one time process [22,23]. To do them repeatedly in real time scenario would be challenging as the mismatch in a Indented Radar would be prominent and unpredictable.…”

Short-Range Noncontact Sensors for Healthcare and Other Emerging Applications: A Review

“…Researchers later developed more advanced demodulation techniques including the complex demodulation [ 54 ] and the arctangent demodulation [ 55 ]. Other signal processing methods such as adaptive DC calibration [ 17 , 56 ], noise cancellation [ 57 ], distortion cancellation [ 58 ], and I / Q mismatch mitigation [ 59 , 60 ] have been proposed to make radar systems robust enough for practical applications. This paper reviews the recent technical advances in CW Doppler radar sensors for healthcare applications, including system hardware improvement, digital signal processing, and chip integration.…”