Biomedical Engineering Reference
In-Depth Information
reliability is low, this could lead to a wrong diagnosis and it can be life
threatening.
• 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.
• Scalability—Data rates for WBAN ranges 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 con-
sidered in a WBAN MAC scheme.
• Latency—WBAN contains time critical data, therefore latency is another
important factor to be considered in a WBAN MAC protocol.
• Interference mitigation—As the WBAN nodes are mobile, the channel con-
dition 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.
• 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.
2.13 Conclusion
An UWB WBAN system should be considered as a combination of a MAC pro-
tocol and the UWB hardware platform. The MAC protocols for UWB systems
should be designed in a way such that it enhances the advantages provided by
UWB signals and overcomes the drawbacks, specially the high complexity of a
receiver. MAC protocols mentioned in this chapter have not considered manipu-
lation of the physical layer properties of the UWB systems such as number of
pulses per data bit, and transmit duty cycle, which can be incorporated with the
MAC algorithm in order to make the system more dynamic in terms of data rate
and QoS. These studies consider UWB for both up-link and down-link commu-
nication; hence they do not consider the complexities introduced by UWB
receivers. Although the transmit-only MAC protocol suggested in [
5
,
24
] addresses
the problem of high power consumption, which arises due to the use of UWB
receiver at the WBAN sensor node, it has several drawbacks. When the network
traffic increases, collisions that occur due to asynchronous transmission of UWB
pulses adversely affect the data delivery capability of the network. There is no
feedback path to dynamically adjust the transmit signal in accordance with the
changing channel conditions. Rescheduling of the network requires manual
intervention with the sensor nodes. It also has to occupy different receiver nodes
for each patient, since different pulse repetitive frequencies are being used to
identify different users.
