# Respiration Rate Extraction of Moving Subject Using Velocity Change in FMCW Radar
## 2 Methods
### The Study Protocol  
The conventional research method, based on \(M(t,\ r_{k})\) of data obtained from the FMCW radar, and the proposed method, based on only \(D_{v}(t)\), are compared in four experiments. The FMCW radar used in the experiment has the MOD602 (Bitsensing Inc., Seongnam, Korea) configuration, as shown in Figure 4, and its parameters are listed in Table 1.  
\[\Delta R=\frac{c}{2 BW} \tag{7}\]  
\[\Delta V=\frac{\lambda}{2\cdot N\cdot T_{C}} \tag{8}\]  
Figure 4: FMCW radar.  
The number of chirps of the FMCW radar used in this paper is 64. The distance resolution can be calculated by Equation (7), and it is 0.05 m. In addition, the velocity resolution can be obtained using Equation (8), and it is 0.15 m/s. The radar shown in Figure 4 has two transmit antennas and four receive antennas. To evaluate the accuracy of the respiration rate extracted using the radar, the actual respiration rate value is required. To this end, a contact-type respiration sensor (Neulog Respiratory Monitor Belt Logger Sensor; Neulog Inc., Rochester, NY, USA) is used to measure the actual exact respiration rate. The respiratory rate data measured by this sensor are used as the ground truth. To implement the conventional research method, the range-bin corresponding to the subject's chest is selected through the range spectrum, and the respiration rate is measured by considering the chest displacement caused by respiration. In experiment (a), the body is in a stationary state, supported by a wall. Both the conventional and proposed methods can achieve an accurate respiration rate in this stationary situation. In subsequent experiments, as shown in Figure 5b-d, the subject stands still without leaning against a wall, is seated on a chair and moves forward and backward, and is seated on a chair and moves left and right, respectively. We compared the accuracy of the respiration rate extraction using the conventional proposed methods. In all experiments, the FMCW radar is installed approximately 0.6 m in front of the subject's chest, as shown in Figure 6. The respiration signal obtained using the contact sensor in the experiments is defined as the ground truth. In addition, the ground truth signal is compared with the signal extracted using a 0.1-0.4 Hz band-pass filter for the conventional approach, and the signal from which DC is removed is extracted using a 0.1 Hz high-pass filter for the proposed approach. Ten subjects were involved in each experiment and were asked to breathe naturally and normally.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Center frequency & 60 GHz \\ Detection range & \(\sim\)6.4 m \\ Bandwidth & 3 GHz \\ Chirp duration & 256 \(\upmu\)s \\ Sampling rate & 1 MHz \\ Scan interval & 50 ms \\ Rx antenna spacing & 0.5 \(\uplambda\) \\ Range revolution & 0.05 m \\ Velocity revolution & 0.15 m/s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Radar parameters and specifications.  
Figure 5: Subject’s postures and movements: (**a**) leaning against the wall; (**b**) without leaning against the wall; (**c**) moving forward and backward; (**d**) moving left and right.