Motivation
The average age of the world’s population has increased because mortality has declined, resulting in an increase of people aged over 65 years during 2010-2030. The growing number of elderly increases the demand for public health care and medical social services. This results in increased health costs and decreased quality of life, since older adults are affected by chronic illnesses that require proper medical care [1]. The following figure shows how the adult population of different countries will evolve until 2050 [2].
![World population ageing: 1950-2050 [2].](doc_images/wban01.png)
Fig. 1. World population ageing: 1950-2050 [2].
The Alliance for Health & Future aims at developing a prosperous society for all people regardless of age, enjoying a healthy and fulfilling life at home, at work, and in their communities [3]. Wireless Body Area Networks (WBANs) are considered a promising solution to health care of people by reducing health care costs and improving quality of life. With these networks people can be monitored continuously and lead a normal life. In this way, hospitals will have more available rooms for people with serious illnesses, while other diseases can be treated at home.
WBANs are used to monitor a person’s vital signs, as depicted in Fig. 2. They are formed by sensors on and/or in the human body, which are responsible for sensing biological signals such as temperature, pulse, movement, electrocardiogram, electromyography, oxygen saturation, etc. Various monitoring technologies have emerged as a solution for health care and are used as a promising means to continuously monitor a person’s health status from a central station or hospital without impeding the person’s mobility.
![Typical WBAN application [4].](doc_images/wban02.png)
Fig. 2. Typical WBAN application [4].
The acquisition of a person’s data can be used for the diagnostic support of clinical personnel. In this application, there are data sets corresponding to physical variables (vital signs). These data sets must be handled with special care ensuring reliability, security, and accuracy since a wrong signal could jeopardize the person’s life or generate unnecessary alerts, rendering the health system inadequate to improve his or her quality of life.
Research problems
Wireless Sensor Networks (WSNs) may be used for monitoring vital signs. Similar to WBANs [5], WSNs use the IEEE standard 802.15.4 [6], which defines the physical (PHY) and medium access control (MAC) layers and serves as the base of the ZigBee specification [7], as shown in Fig. 3. ZigBee benefits from low energy consumption and cost and is approved by the Continua Health Alliance [8] as a suitable solution for health care applications.
![ZigBee specification [4].](doc_images/wban03.png)
Fig. 3. ZigBee specification [4].
To improve WBAN performance, quality-of-service (QoS) solutions have been proposed at the MAC layer level, where the behavior of MAC protocols such as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) are investigated in detail. An interesting research can be to find an efficient solution for WBANs such that they have a better performance in terms of QoS metrics, e.g., delay, throughput, energy consumption, packet loss, and priority, among others.
Another solution for improving WBAN performance is the so-called Impulse Radio-Ultra Wide Band (IR-UWB) technology, which is used for high data rate applications. This technology can be used in wireless health monitoring applications due to its low power consumption, high data rates, low cost, and multipath fading detection in indoor environments. Also, UWB permits the reuse of spectrum.
MAC protocols in WBANs: performance metrics
MAC protocols operate at the link layer and are responsible for coordinating channel access, achieve maximum transfer rates, and avoid collisions. In addition, they should ensure minimal latency and low power consumption.
An efficient MAC protocol for WBAN applications should meet the following performance requirements.
Energy efficiency
It is important that WBANs have nodes operating for a long time, even though the battery of nodes can be affected by overhead, idle listening, collisions, over-emitting, and overhearing.
QoS
This term may have different meanings depending on the application [5]. It is important to ensure network reliability, security, and accuracy since they may generate alerts, thus jeopardizing the patient’s life.
Priority traffic
MAC protocols must allow the delivery of critical data with the least possible latency and must be also reliable.
Heterogeneous traffic
The network must handle various traffic types with low to high data rates.
Scalability
It is very important to consider this factor, because WBANs may vary with respect to the number of nodes such that the network is able to tolerate such changes.
Interoperability
WBANs may have multiple PHY techniques and must connect many devices working on different bands.
Latency
If a WBAN carries critical data, they must be sent as soon as possible.
Network structure
A star topology, scalable network size, and a sensor device communicating to a WBAN that can be implemented in a PDA or laptop.
Security and privacy
The communication between sensors in a WBAN is confidential and should be encrypted to protect the person’s privacy, at the expense of an increased energy consumption.
Research directions
The most important attribute of a WBAN MAC protocol is energy efficiency. Depending on the application, some sensors will require a battery lifetime of months, years, or only a few hours. Flexible duty cycle techniques are required to minimize idle listening, packet collisions, overhearing, packet overhead, and latency. A MAC protocol for WBANs should consider electrical properties of the human body and diverse nature of traffic nodes (in-body and on-body) and may be based on UWB technologies. Therefore, it is important to identify how we can simplify and modify them for WBANs, giving rise to novel MAC protocols.
Another important research direction is the co-existence with home area networks (HANs) based on ZigBee and WiFi. These networks integrate a variety of computers, network communication and electrical devices. A HAN permits to centralize the management and services in a house and helps people optimize their living style. It helps reduce bills and energy consumptions in a house.
WBAN architecture design
The network consists of nodes (end devices) that communicate with a central node (coordinator) using a star topology. The nodes are connected with vital sign sensors and are responsible for sending the information captured by them to the central node of the network, as shown in Fig. 4. The coordinator in turn sends the information to a remote server or hospital. Typically, the end devices are located in/on the human body and the coordinator is located outside the human body.
Fig. 4. WBAN architecture.
Sensors
These devices sense the biological variables of a person’s body, including temperature, pulse, movement, oxygen saturation, among others, and communicate with WBAN nodes.
QoS metrics
New performance metrics are to be defined apart from conventional QoS metrics such as delay, packet loss, power consumption, throughput, priority, jitter, reliability, etc.
Processing algorithms
It is necessary to implement algorithms for processing a person’s biological signals in order to analyze the measurements made by the respective sensors. These algorithms can be implemented in the nodes or coordinator, but it is preferable to implement them at the central node because the other nodes have memory and energy constraints. The coordinator (cell phone, PDA) can be connected to a battery or power outlet.
Experimental system
There are many platforms for wireless sensor networks, for example Tmote Sky, TelosB, MICAZ, MICA2, IRIS, Imote2, etc. Among the most important for healthcare applications is Shimmer [9]. As shown in Fig. 5, Shimmer is a small wireless sensor platform that can record and transmit physiological and kinematic data in real-time. Designed as a wearable sensor, Shimmer incorporates wireless ECG, EMG, GSR, accelerometer, Gyro, Mag, GPS, tilt, and vibration sensors. Shimmer is an extremely extensible platform that enables researchers and engineers to be at the leading edge of sensing technology.
![SHIMMER platform [6].](doc_images/wban05.png)
Fig. 5. SHIMMER platform [6].
Researchers
Advisors
- Prof. Tiago H. Falk
- Prof. Martin Maier
Graduate Student
- Diana Patricia Tobón Vallejo
Publications
- D. P. Tobón, T. H. Falk, and M. Maier,
“MS-QI: A Modulation Spectrum-Based ECG Quality Index for Telehealth Applications,”
IEEE Transactions on Biomedical Engineering, to appear
- D. P. Tobón, T. H. Falk, and M. Maier,
“Context Awareness in WBANs: A Survey on Medical and Non-Medical Applications,”
IEEE Wireless Communications, Special Issue on Wireless Networking for e-Health Applications, vol. 20, no. 4, pp. 30-37, Aug. 2013
- D. P. Tobón Vallejo and N. Gaviria,
“Quality of Service Strategies at Layer Level of Media Access in the IEEE 802.15.4 Standard: State of the Art,”
Proc., First International Conference in Telecommunications, Santo Tomás University, Bucaramanga, Colombia, 2011
References
[1]
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CDC,
“Center for Desease Control and Prevention,”
March 15, 2012 (www.cdc.gov).
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[2]
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Philips,
“Healthcare strategies for an ageing society,”
The Economist Intelligence Unit Limited, pp. 2-28, 2009.
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[3]
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OECD,
“Better policies for better lives,”
March 15, 2012 (www.oecd.org).
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[4]
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E. Jovanov et al,
“A Wireless Body AreaNetwork of Intelligent Motion Sensors for Computer Assisted Physical Rehabilitation,”
Journal of Neuroengineering and Rehabilitation, pp. 2-6, 2005.
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[5]
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M. A. Ameen et al,
“QoS Issues with Focus on Wireless Body Area Networks,”
Proc., International Conference onConvergence Information Technology, Los Alamitos, CA, USA, vol. 1, pp. 801-807, 2008.
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[6]
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IEEE,
“IEEE Standard for Information Technology - Telecommunications and Information Exchange Between Systems - Local and Metropolitan
Area Networks - Specific Requirements Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for
Low-Rate Wireless Personal Area Networks (WPANs),”
IEEE Std 802.15.4-2006 (Revision of IEEE Std 802.15.4-2003), 2006.
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