RespTracker:Multi-user Room-scale Respiration Tracking with Commercial Acoustic Devices Haoran Wan,Shuyu Shi,Wenyu Cao,Wei Wang,Guihai Chen State Key Laboratory for Novel Software Technology,Nanjing University [wanhr,wenyucao}@smail.nju.edu.cn,[ssy,ww,gchen}@nju.edu.cn Abstract-Continuous domestic respiration monitoring provides vital information for diagnosing assorted diseases.In this paper,we introduce RESPTRACKER,the first continuous, multiple-person respiration tracking system in domestic settings using acoustic-based COTS devices.RESPTRACKER uses a two-stage algorithm to separate and recombine respiration signals from multiple paths in a short period so that it can track the respiration rate of multiple moving subjects.Our experimental results show that our two-stage algorithm can distinguish the respiration of at least four subjects at a distance of three meters. I.INTRODUCTION Background and Motivation:Respiration is one of the vi- tal signs that contain valuable information to diagnose assorted diseases,e.g.,pulmonary disease [1],heart failure [2],anxi- Figure 1.General application scenario of RESPTRACKER. ety [3].and sleep disorders [4].Clinical instruments,such as capnography or plethysmography,provide reliable respiration measurements.However,they need professional operators and for a Wi-Fi bandwidth of 40 MHz.Existing works either cannot be deployed in the domestic scenario to perform long- rely on the differences in the respiration rate [11]or use term monitoring,which is vital to early diagnoses of chronic specialized high bandwidth frequency modulated continuous diseases,such as obstructive sleep apnea syndrome (OSAS) wave (FMCW)radar and Independent Component Analysis and chronic obstructive pulmonary disease (COPD).As a (ICA)[9]to separate multiple users.These solutions impose result,the development of domestic continuous respiratory extra assumptions on respiration patterns or need specialized monitoring systems has attracted increasing research interest devices that increase the domestic deployment cost.Acoustic- in recent years. based systems turn the speaker-microphone pair integrated There are domestic respiratory monitoring systems based with COTS devices,such as mobile phones and smart speak- on cameras [5]or using special devices,including belt integ- ers,into an active sonar to perform the respiration monitoring rated with capacitive sensors 6]or smart cushion with air task.The advantage of acoustic-based systems is the higher pressure sensors [7].However,user studies have shown that range resolution [10],e.g.,a typical bandwidth of 4kHz people are reluctant to deploy these devices due to privacy leads to a range resolution of 8.5 cm for ultrasound signals. concerns [5],[8]or the high cost and long-term physical However,due to the fast attenuation of sound signals,most contact requirements [6],[7].A more promising solution is acoustic-based systems have a limited range of 0.7~1.1 m enabling device-free respiratory monitoring with ubiquitously [10].[13],[14].Therefore,their applications are limited to available wireless signals emitted by commercial off-the-shelf sleep monitoring instead of room-scale domestic deployment (COTS)devices in domestic settings [9]-[11]. for continuous respiratory monitoring and tracking. Limitations of Prior Art:Existing device-free respiratory Proposed Approach:In this paper,we introduce monitoring systems leverage two types of signals emitted RESPTRACKER,the first continuous,multiple-person respira- by COTS devices:radio frequency (RF)signals and ultra- tion tracking system in domestic settings using acoustic-based sound signals.One popular solution for RF-based systems is COTS devices.As shown in Figure 1,the respiration signal collecting Wi-Fi channel state information(CSD)for further of different users may arrive at the receiver through multiple respiration measurements [12].However,due to the narrow paths.RESPTRACKER proposes a multipath separation and bandwidth of Wi-Fi signals,the range resolution of CSI is too combination framework for robust respiration signal tracking. low to separate two nearby respiration signals.For example, First,RESPTRACKER utilizes inaudible sound signal mod- the aliasing range between two non-resolvable paths is 7.5 m ulated by the Zadoff-Chu (ZC)sequence to separate sound re- flections from different users.Compared to traditional FMCW- Shuyu Shi is the corresponding author. based systems,the key advantage of our separation schemeRespTracker: Multi-user Room-scale Respiration Tracking with Commercial Acoustic Devices Haoran Wan, Shuyu Shi, Wenyu Cao, Wei Wang, Guihai Chen State Key Laboratory for Novel Software Technology, Nanjing University {wanhr, wenyucao}@smail.nju.edu.cn, {ssy, ww, gchen}@nju.edu.cn Abstract—Continuous domestic respiration monitoring provides vital information for diagnosing assorted diseases. In this paper, we introduce RESPTRACKER, the first continuous, multiple-person respiration tracking system in domestic settings using acoustic-based COTS devices. RESPTRACKER uses a two-stage algorithm to separate and recombine respiration signals from multiple paths in a short period so that it can track the respiration rate of multiple moving subjects. Our experimental results show that our two-stage algorithm can distinguish the respiration of at least four subjects at a distance of three meters. I. INTRODUCTION Background and Motivation: Respiration is one of the vi￾tal signs that contain valuable information to diagnose assorted diseases, e.g., pulmonary disease [1], heart failure [2], anxi￾ety [3], and sleep disorders [4]. Clinical instruments, such as capnography or plethysmography, provide reliable respiration measurements. However, they need professional operators and cannot be deployed in the domestic scenario to perform long￾term monitoring, which is vital to early diagnoses of chronic diseases, such as obstructive sleep apnea syndrome (OSAS) and chronic obstructive pulmonary disease (COPD). As a result, the development of domestic continuous respiratory monitoring systems has attracted increasing research interest in recent years. There are domestic respiratory monitoring systems based on cameras [5] or using special devices, including belt integ￾rated with capacitive sensors [6] or smart cushion with air pressure sensors [7]. However, user studies have shown that people are reluctant to deploy these devices due to privacy concerns [5], [8] or the high cost and long-term physical contact requirements [6], [7]. A more promising solution is enabling device-free respiratory monitoring with ubiquitously available wireless signals emitted by commercial off-the-shelf (COTS) devices in domestic settings [9]–[11]. Limitations of Prior Art: Existing device-free respiratory monitoring systems leverage two types of signals emitted by COTS devices: radio frequency (RF) signals and ultra￾sound signals. One popular solution for RF-based systems is collecting Wi-Fi channel state information (CSI) for further respiration measurements [12]. However, due to the narrow bandwidth of Wi-Fi signals, the range resolution of CSI is too low to separate two nearby respiration signals. For example, the aliasing range between two non-resolvable paths is 7.5 m Shuyu Shi is the corresponding author. Figure 1. General application scenario of RESPTRACKER. for a Wi-Fi bandwidth of 40 MHz. Existing works either rely on the differences in the respiration rate [11] or use specialized high bandwidth frequency modulated continuous wave (FMCW) radar and Independent Component Analysis (ICA) [9] to separate multiple users. These solutions impose extra assumptions on respiration patterns or need specialized devices that increase the domestic deployment cost. Acoustic￾based systems turn the speaker-microphone pair integrated with COTS devices, such as mobile phones and smart speak￾ers, into an active sonar to perform the respiration monitoring task. The advantage of acoustic-based systems is the higher range resolution [10], e.g., a typical bandwidth of 4kHz leads to a range resolution of 8.5 cm for ultrasound signals. However, due to the fast attenuation of sound signals, most acoustic-based systems have a limited range of 0.7∼1.1 m [10], [13], [14]. Therefore, their applications are limited to sleep monitoring instead of room-scale domestic deployment for continuous respiratory monitoring and tracking. Proposed Approach: In this paper, we introduce RESPTRACKER, the first continuous, multiple-person respira￾tion tracking system in domestic settings using acoustic-based COTS devices. As shown in Figure 1, the respiration signal of different users may arrive at the receiver through multiple paths. RESPTRACKER proposes a multipath separation and combination framework for robust respiration signal tracking. First, RESPTRACKER utilizes inaudible sound signal mod￾ulated by the Zadoff-Chu (ZC) sequence to separate sound re- flections from different users. Compared to traditional FMCW￾based systems, the key advantage of our separation scheme