Biomedical Engineering Reference
In-Depth Information
Synchronization
Frame
Guard
Interval
SYNC
PHR
Guard
Interval
Data Frame
Preamble
Data
Fig. 2.8
Frame structure for Transmit-only MAC protocol for WBAN
for data reception. The data frame overhead is kept to a minimum in order to keep
the transmission period short and thus reducing the chances of collision.
Drawbacks: Although the transmit-only MAC protocol 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, the number of collisions, which occur due to
asynchronous transmission of pulses, adversely affect the data delivery capa-
bility in the network.
• There is no feedback path to dynamically adjust the transmit power in accor-
dance with the changing channel conditions.
• Rescheduling of the network requires manual intervention with the sensor
nodes.
This MAC protocol can be further improved by the use of a narrow band
receiver in order to eliminate the issues regarding the network reconfigurations and
network expansion while achieving low power consumption in the sensor nodes.
Such a MAC protocol is suggested in [
27
]. The MAC protocol described in [
27
]
uses a narrow band receiver at the sensor node to receive feedback on properties,
such as receive BER. This MAC protocol will be discussed further in
Chap. 3
.
2.12 Comparison of UWB-Based MAC Protocols
for WBAN Applications
The MAC protocols discussed above have advantages in different areas when they
are used in WBAN applications. A summary of the selected MAC schemes dis-
cussed in this section is tabulated in Table
2.1
based on their performance attri-
butes described below.
• Energy efficiency—Factors affecting the energy efficiency of a MAC scheme
are energy wastage due to protocol overhead, idle listening, collisions, over-
emitting and overhearing.
• QoS—Quality of Service (QoS) is crucial in a WBAN system due to the sen-
sitivity of the data collected by sensor nodes. If the QoS is poor and the data
