VitalCSI: Contactless Respiratory Rate Estimation Using Consumer-Grade Wi-Fi Channel State Information

Journal article

Continuous respiratory rate (RR) monitoring can improve the detection of clinical events, such as pulmonary infections, cardiac arrests, and sleep apnoea. Wi-Fi-based systems offer a low-cost, contactless alternative to radar and video. However, existing studies are limited to narrow respiratory ranges and small-scale validation. We present VitalCSI, a vital sign monitoring system using off-the-shelf, low-power Wi-Fi hardware. We recorded 15 healthy university athlete volunteers and developed RR estimation algorithms benchmarked against nasal airflow sensors. VitalCSI uses a consumer Wi-Fi access point and a Raspberry Pi computer to capture channel state information (CSI). We estimated the RR from CSI via principal component analysis (PCA), spectral peak detection, and breath (counting in 30 s windows), which were then fused by a multidimensional Kalman filter. VitalCSI showed strong agreement with airflow references (r2=0.93, MAE = 1.20 brpm), tracking RR across 6–33 brpm and outperforming prior Wi-Fi studies. VitalCSI demonstrates the feasibility of RR monitoring with a single-antenna, single-board microcomputer as the Wi-Fi transmitter. It is the first validated system for continuous, contactless RR monitoring using consumer-grade Wi-Fi over an extended respiratory range, paving the way for use in both home and sports monitoring contexts.

Authors: Michaelis, T; Jorge, J; Bijlani, N; Villarroel, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: MDPI
• Journal: Sensors
• Volume: 26
• Issue: 1
• Pages: 225
• Article number: 225
• Publication date: 2025-12-29
• Acceptance date: 2025-12-24
• DOI: 10.3390/s26010225
• EISSN: 1424-8220
• ISSN: 1424-8220
• Language: English
• Keywords: Wi-Fi; respiratory rate (RR) monitoring; channel state information (CSI); continuous monitoring