In Wireless Sensor Networks (WSNs), a number of tiny, battery-powered com- puting devices are scattered throughout a physical environment. Each device is capable of sensing, and transmitting information. It is a packaged data collection and transmission component, which consists of a sensor module, an embedded processor, a transceiver module, and a power delivery mechanism. Components are held within an enclosure.
A sensor board is the part that actually interacts with the environment and sends an appropriate signal to the embedded processor (microcontroller unit).
The Shimmer ECG board is an example [Shimmer, 2013]. The microcontroller
unit may decide to forward the sensed signal to a base station, or to do some processing locally. When ready, the processor sends the signal to the transceiver board which contains the radio stack and antenna; the transceiver then uses a communications protocol (e.g. IEEE 802.15.4, Bluetooth, ZigBee) to pass the information to the base station.
WSNs have been used in commercial, industrial, and academic applications to monitor data that would be difficult or expensive to be captured using wired sensors. A variety of applications have been presented in the literature for wire-
less sensor networks. These include environmental monitoring [Oliveira and Ro-
drigues,2011], building monitoring [Yoon et al.,2011], natural disaster prevention
[Chen et al., 2013], and structural health monitoring [Hu et al., 2013]. Recently,
researchers have investigated the potential of developing WSNs for healthcare
systems [Aminian and Naji, 2013; Caldeira et al., 2012; Peiris, 2013]. What dif-
ferentiates healthcare from other WSN technology applications is the criticality of the application and the human centred aspect. To design a WSN for the solu- tion of healthcare problems, the following key principles should be kept in mind throughout the process:
• This is a healthcare problem, not a technology problem. The patient plays the decisive role, not the technology.
• There is often more than one approach to achieve a clinical or care objective. • The simpler the technology, the better the solution.
• It has to work in the home, not just in the lab.
Concerning the ability of the WSN to function properly and the impact on the safety of patients and caregivers, a range of new factors must be considered, not only technological but also user-centred and healthcare associated, at all stages of designing a WSN architecture for healthcare solutions. The most essential requirements include: Cost Efficiency, Fault Tolerance, Stability and Scalability,
Low Power Consumption, Long-term Usability, Privacy and Security. However, the interpretation and implementation of these guidelines totally depends on the particular design of each healthcare application. In some cases, not all the points above will be relevant.
Wireless Body Area Network (WBAN) Wireless Sensor Network (WSN)
Users GPRS/3G Healthcare Professional Hospital Facilities Remote Family/ Caregiver Medical Servers
Tier 1 Tier 2 Tier 3
Internet
Figure 2.3: Generalized WSN architecture for pervasive healthcare
Figure 2.3 shows a generalized WSN architecture for pervasive healthcare.
While this does not illustrate any specific system, it shows the components of a pervasive healthcare system and their relationships with one another. At the core of the system is the user, also referred to as the ”subject” (in a research environment) and as the ”patient” (in a clinical or therapeutic environment). The user is monitored by wireless sensor networks. This is referred to as Tier 1. The information gathered by the components of the WSN is sent to a base station, or home gateway (often a PC or a smart phone) for data processing and analysis. This is referred to as Tier 2. The communication links used between the WSN and the home gateway will vary according to circumstances (e.g. ZigBee, Bluetooth, WiFi). The home gateway connects over the internet and/or other long range communications protocols to various Tier 3 services. These may in- clude a medical server, a healthcare provider, a family member, a caregiver and emergency services etc. Again, a range of communications protocols are possible
here, depending on the requirements of the particular problem domain [Dishongh
and McGrath, 2010].
More and more prototype and commercial systems for pervasive healthcare monitoring have been developed for the elderly, and chronically ill people, using the generalized WSN architecture. After exploring these systems, it is observed that the main application areas include:
• Activities of daily living monitoring [Benzo et al.,2014;Charlon et al.,2013;
Lu and Fu,2009].
• Fall and movement detection [Gannot et al., 2013; Schwickert et al., 2013;
Wang et al., 2008].
• Location tracking [Lee et al.,2013;Marco et al.,2008;Thomas et al.,2013].
• Medication adherence prompting [Chen et al.,2014;Chu,2013;Pang et al.,
2009].
• Medical status monitoring [Kailanto et al., 2008; Tharion et al., 2013; Tri-
antafyllidis et al.,2013].
In the first category, applications try to identify and differentiate everyday activi- ties of the patients and the elderly such as watching television, sleeping, preparing meals, and be able to detect abnormal conditions. Fall and movement detection applications are focused on physiological conditions such as posture and fall de- tection for people that need special care like the elderly people who are susceptible to falls. Location tracking, medication intake reminders and monitoring systems can help cognitively impaired people to survive independently. Medical moni- toring applications make use of medical and environmental sensors in order to obtain comprehensive health status information of the patients, including ECG, heart rate, blood pressure, skin temperature, and oxygen saturation.
In this dissertation, a comprehensive WSN is developed, incorporating body area network and smart home sensors, to achieve monitoring of a person and surroundings in a home environment. Distinguished from existing works, which mostly focus on a single application area as listed above, the WSN is dedicated to gather as much as possible information about and around a person to cover multiple tasks of a healthcare application.