Abstract
The quadrature continuous-wave (QCW) radar has been extensively studied for small vibrational displacement detection such as non-contact sensing of human vital signals. One of the challenges of the QCW radar is the IQ-imbalance and DC-offset estimation by using curve fitting algorithms. Many algorithms have been proposed and have shown that the fitting error increases when the displacement length is small, in which case sufficient data is not provided to the algorithms. This paper presents a quadrature frequency-group (QFG) radar which utilizes a group of frequencies to enhance the fitting performance even with the small displacement. The grouped-frequencies in the QFG radar gives more data than the single-tone of the QCW radar under the same displacement condition. This paper presents the framework and properties of the QFG radar. Some fitting algorithms for the QFG radar are presented and the most adequate algorithm is suggested by simulation and experiments. Simulation and experimental results shows that the QFG radar outperforms the QCW radar. Specifically, it is shown that the fitting accuracy of the QFG radar is up to 100 times better than the QCW radar in the experiment.
Highlights
Small displacement induces the phase change of the baseband signal of the quadrature continuous-wave (QCW) radar, and it can be detected by linear or non-linear demodulation method4
After the IQ-imbalance correction as described in previous section, the baseband signals of the quadrature frequency-group (QFG) radar are shown in Fig. 10 for four different bands fc = 400 MHz, 2.4 GHz, 10 GHz, 24 GHz
The relative errors of the displacement calculation are 2.3%, 1.4%, and 0.8%, respectively. These results are comparable with the results using CW Doppler radar39, where the results39 used the pre-calibration step to get the DC-offset using sufficiently long arc while the QFG radar uses no pre-calibration step
Summary
Small displacement induces the phase change of the baseband signal of the QCW radar, and it can be detected by linear or non-linear demodulation method. Common point in the literature is that the center estimation performance increases when the elliptic arc is sufficiently long. To secure such a long arc, a pre-calibration step is preferred for radar systems. Huang et al. presented a semi-definite programming algorithm for center estimation of the short arc. It requires no calibration environment, and the center estimation is performed using only the target’s small displacement. Disadvantage of the semi-definite programming is high computational complexity, where the worst case complexity is bounded to O(n6) Another approach to make sufficiently long elliptic arc without pre-calibration step is proposed. The experimental results show that the fitting accuracy of the QFG radar is up to 100 times better than the QCW radar
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