Instrumentation & Measurement Magazine 24-2 - 33

2). The ending shows the participant awake but lying in bed
with the covers exposed and therefore relates to the cooler temperature and high HRV activity.
Heaters and air conditioning units can regulate the temperature during sleep but could be expensive to use all night
during sleep. Cold temperature may not affect sleep as much,
however, as people normally sleep with clothing and bedding
to create a comfortable microclimate which regulates their
body temperature [13]. An individual can adjust how much of
their body is covered under the bedding to maintain an appropriate balance of the microclimate and external temperatures
allowing them to cool or warm up during sleep. However, during warmer environments, it could be difficult to cool down
their body temperature, as the ambient environment could still
be too hot even without any bed covers over their body. Environmental factors can affect people during their sleep, and the
following section describes the experimental setup for the demonstrative IoT platform that combines both wearable and
non-wearable sleep tracking devices to evaluate sleep quality
and validate the impact of the ambient environment.

Experimental Setup
Fig. 3 shows the bedroom setup for the IoT platform with a volunteer sleep study participant donning a full PSG system with
an inertial measurement unit (IMU) for actigraphy and a noncontact BCG device on the mattress. The portable Embletta®
X100 PSG system from Embla Systems Inc. (Broomfield, CO,
USA) was used as the reference to all the sleep scores. The sensors employed by Embletta® X100 are EEG, EMG, ECG, EOG,
respiration bands, pulse oximetry and nasal cannula. The BCG
sensor used was the SCA11H bed sensor from Murata Manufacturing Co. Ltd. (Nagaokakyo, Kyoto, Japan). In addition,
environmental data loggers were placed around the room to

measure temperature, humidity, light and sound, and a temperature/humidity probe was placed in the bed to measure the
microclimate under the bedsheet. This study was approved by
the Simon Fraser University Office of Research Ethics (study
no. 2017s0629). The BCG sensor output heart rate (HR), HRV,
respiration rate (RR), respiration depth, stroke volume (SV),
B2B intervals, and time [15]. It was attached to the bedsheet on
the mattress through a magnetic clamp so it would not move
around during the night. The actigraphy sensor used was the
Xsens MTw Awinda wireless motion tracker (Enschede, Netherlands) that comprises tri-axial accelerometers, gyroscopes,
and magnetometers [19]. It was attached to the non-dominant
arm with a hook and loop strap that was easy to fasten right before lying to sleep. The environmental sensors comprised the
Ubibot WS1 Pro, to measure temperature, humidity, and light
in the room, with a sensing probe placed in the bed while the
participant slept to measure microclimate temperature and
humidity. Finally, the Tekcoplus sound level meter with data
logging function was used to measure the decibel level in the
room throughout the night.
As a demonstration example for this paper, a sleep experiment was carried out on the volunteer participant, over six
nights for at least seven hours of sleep each night. It also served
as a pilot human trial to evaluate the feasibility of deploying
all IoT sensors and PSG to a participant's home for an at-home
sleep test versus a more expensive and less convenient in-lab
test. As multiple devices were employed for the study, time
synchronization was an important factor to have device signals matched up as closely as possible. Most of the devices
offered an internal clock that would create a timestamp so
they could be synchronized. The PSG had specific sampling
frequencies for each device and would output sleep scores every 30 seconds. The sound, light and humidity sensors had a

Fig. 3. Full system setup. (a) Environmental sensors placed beside the bed; (b) Participant with all the devices and sensors attached.
April 2021	

IEEE Instrumentation & Measurement Magazine	33



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