Biomedical Engineering Reference
In-Depth Information
Fig. 3.15 Variation of the
percentage throughput for
each sensor type in the two
simulated topologies
100
90
80
70
60
50
40
30
Topology 1-Continuous sensors
Topology 2-Continuous sensors
Topology 1-Periodic sensors
Topology 2-Periodic sensors
20
10
0
1
2
3
4
5
6
7
Number of Patients
periodic nature, there is a possibility of sudden network load increase when a set of
sensor nodes from a patient is turned on at the same time. This should not hinder
the capability of the network to deliver the offered traffic from the sensor nodes.
Since priority is given for critical physiological data, throughput of continuous
data should be kept at a high value throughout the period of data transmission.
Periodic signals like body temperature and heart rate are comparatively less time
critical. Hence it is reasonable to allocate higher percentage of network capacity
for continuous sensor nodes while dynamically varying the network capacity
allocated for periodic sensors.
From Fig.
3.15
it can be seen that throughput percentage that can be achieved
for both continuous and periodic traffic in Topology 1 is higher than that of
Topology 2. Router nodes in Topology 1 offer channel resources only to their child
nodes while in Topology 2, channel resources from coordinator node are shared
between all the sensor nodes.
The throughput percentage for periodic data decreases with increasing sensor
nodes in all two topologies. This is due to the fact that as the contention free traffic
increases, timeslots available in the super frame for a contention based traffic
decrease. The priority is given to continuous sensor nodes that transmit data in the
contention free period.
3.5.4 Energy Consumption
A system with low power consumption will allow the battery powered sensor nodes
in a WBAN to operate in an autonomous manner with less human intervention.
From Fig.
3.16
it can be observed that the consumed energy at sensor nodes per
useful bit is comparatively higher in Topology 2, which does not use an interme-
diate router. This power consumption value contains the power consumed for
retransmissions as well. From the simulations it is observed that the number of
retransmissions in Topology 1 is less than that of Topology 2 due to the distributed
