Vital sign monitoring is a critical step in health assessment in clinical settings. A rising interest in contactless options is pushing for innovative solutions for heart rate (HR) and respiration rate (RR) estimation. Low-power millimeter-wave radars are emerging as a solution because of their invariance to lightning conditions, subject phenotype, and privacy guarantees. On the side, the robustness of radar-based systems is still a concern due to incomplete characterization of the systems, evaluation of different frequencies, and limited evaluation on human subjects. Moreover, low-power options have not been rigorously explored, despite their potential in ubiquitous deployment. This article evaluates three low-power frequency-modulated continuous wave (FMCW) radars with the frequencies of 24, 60, and 120 GHz, investigating their performance and the influence of the carrier frequency in vital sign estimation. An initial characterization of the displacement noise is conducted using a phantom device. Various techniques to enhance the signal to noise ratio (SNR) of the radar signal and the extraction of the chest displacement signal are combined. Finally, a lightweight and accurate algorithm based on the second-order derivative of the displacement is proposed, developed, and evaluated to assess the HR and RR. The evaluation is conducted for all three radar systems on a dataset with 24 subjects. We demonstrate with the experimental evaluation that the three systems accurately estimate the RR with a mean absolute error (MAE) of less than 2 brpm (±3.05). The 60- and 120-GHz system estimates the HR accurately with an MAE of 1.8 ± 3.1 bpm and 3.2 ± 5.3 bpm, respectively, while the 24-GHz system is less effective with an MAE of 9.0 bpm, mainly due to its high noise profile. This evaluation demonstrates the feasibility of HR and RR with low-power FMCW radars, underlying the importance of the operating frequency, and the necessity of an appropriate characterization when designing the algorithms.

中文翻译：

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频率很重要：用于生命体征监测的低功率 FMCW 雷达的比较分析

生命体征监测是临床环境中健康评估的关键步骤。人们对非接触式选项的兴趣日益浓厚，正在推动心率 (HR) 和呼吸率 (RR) 估计的创新解决方案的发展。低功率毫米波雷达因其对闪电条件、主体表型和隐私保证的不变性而成为一种解决方案。另一方面，由于系统的表征不完整、不同频率的评估以及对人体的评估有限，基于雷达的系统的鲁棒性仍然是一个问题。此外，尽管低功耗选项具有普遍部署的潜力，但尚未经过严格的探索。本文评估了频率为 24、60 和 120 GHz 的三种低功率调频连续波 (FMCW) 雷达，研究它们的性能以及载波频率对生命体征估计的影响。使用模型设备进行位移噪声的初始表征。结合了增强雷达信号的信噪比（SNR）和提取胸部位移信号的各种技术。最后，提出、开发和评估了一种基于位移二阶导数的轻量级精确算法，以评估 HR 和 RR。该评估是在包含 24 个受试者的数据集上对所有三个雷达系统进行的。我们通过实验评估证明，这三个系统可以准确估计 RR，平均绝对误差 (MAE) 小于 2 brpm (±3.05)。 60 GHz 和 120 GHz 系统可准确估计 HR，其 MAE 分别为 1.8 ± 3.1 bpm 和 3.2 ± 5.3 bpm，而 24 GHz 系统的 MAE 为 9.0 bpm 时效率较低，这主要是由于其高噪声轮廓。该评估证明了 HR 和 RR 与低功率 FMCW 雷达的可行性、工作频率的重要性以及设计算法时适当表征的必要性。