Biomedical Engineering Reference
In-Depth Information
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Priority traffic
—In a WBAN system, the MAC should be able to support on-
demand traffic and provide a method for critical data to be transmitted reliably
with minimum latency.
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Scalability
—Data rates for WBAN range from a few kilobytes to tens of
megabytes. The number of nodes in a WBAN system can vary from a single node
to tens of nodes. Therefore, scalability is an important factor to be considered in
a WBAN MAC scheme.
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Latency
—WBAN contains time critical data, therefore latency is another impor-
tant factor to be considered in a WBAN MAC protocol.
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Interference mitigation
—As the WBAN nodes are mobile, the channel condition
is constantly changing. The channel condition deteriorates significantly in areas
densely populated with other WBAN users. The MAC scheme should be resilient
to multiple network interference.
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Channel access
—A WBAN constitutes of both implantable and on-body nodes.
When selecting a channel access scheme, type of the nodes and the physical layer
characteristics should be taken into consideration in order to ensure the reliability
of the system.
Conclusion
Low power consumption and reliable operation are the two of the utmost important
considerations when developing a WBAN system. In order to develop a platform to
satisfy these two requirements, a cross-layer solution that involves both the PHY and
MAC layer is required. The IEEE 802.15.6 standard is recently released in order to
standardize the WBAN communication. Although the IEEE802.15.6 standard pro-
vides a good platform for WBAN applications, it lacks some critical properties when
it comes to using the unique feature of the UWB signals for WBAN applications.
The IEEE 802.15.4a MAC is commonly used as a reference scheme for developing
new MAC protocols for UWB-based WBAN application and as a baseline indica-
tor for performance comparison. Power saving is achieved in a MAC protocol by
reducing the need for retransmission and overhearing. A MAC protocol can be used
to overcome the hardware limitation of a WBAN platform. For example, the power
consumption of a UWB-based WBAN platform can be significantly reduced by using
a MAC scheme that minimizes the use of the receiver. Except for the transmit-only
MAC, all the other MAC protocols have ignored the complexity that arises by using
a UWB receiver at a power critical WBAN sensor node. Although the transmit-only
MAC avoids this by using a transmit-only mechanism, it lacks the ability to dynam-
ically adjust the sensor nodes according to the changing network conditions. The
use of a simple narrowband receiver instead of an UWB receiver will avoid most of
these problems; however, the MAC protocols have to be adjusted in order to achieve
optimized data communication using this method.
In conclusion, this chapter has highlighted the requirement and characteristic
of UWB-based WBANs. A comparison of the various wireless schemes and MAC
protocols for UWB-based WBAN applications is presented.
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