Biomedical Engineering Reference
In-Depth Information
Fig. 3.16 Variation of
consumed energy by a sensor
node per useful data bit (in
nJ) with increasing number of
patients for two topologies
and for sensor nodes with
narrowband receivers and
sensor nodes with UWB
receivers
14
13
Topology 1-with NB feedback
Topology 2-with NB feedback
Topology 1-with UWB feedback
Topology 2-with UWB feedback
12
11
10
9
8
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
Number of Patients
nature of the network. It should be noted that the router node is not required to be
implantable or wearable; it can be kept at close proximity to its child sensor nodes.
Both wearable and implantable sensor nodes should be designed to maximize the
power savings, especially in health monitoring. For example, it is not practical to
recharge a wearable ECG data transmitter frequently. It should be designed to
operate without any intervention as long as possible. In the Topology 1, which uses
a router, the transmit power of the sensor node can be kept at a minimum in order to
achieve a given bit error rate (10
-4
in this simulation). Hence the number of pulses
that needs to be transmitted is comparatively lower than a sensor node in Topology
2. Since the channel characteristics at the receiver are fairly constant over short
distance, the need of dynamically changing the number of pulses is lessen. Because
of all these factors the sensor nodes in Topology 1 consume less power than sensor
nodes of Topology 2. Energy consumption is also compared between sensor nodes
with a narrow band receiver and a UWB receiver. From the obtained results it is
obvious that the use of narrow band receiver reduces the power consumption sig-
nificantly in the sensor node compared to the use of an UWB receiver. It should be
noted that only transmitter and receiver power consumption figures are considered
in these simulations and the power consumption of peripheral electronics are not
considered since they affect all communication scenarios in a similar manner.
3.5.5 Comparison of Some Existing MAC Protocols
A comparison of the MAC protocol presented in this chapter with some of the
existing MAC designs in the literature is shown in Table
3.5
. The UWB MAC
protocol discussed in this chapter demonstrates the ability to change the number of
pulses per data bit in real-time. Thus, it is possible to cater variable data rate
requirements while keeping the network utilization at a maximum level for high
priority sensor nodes. The MAC protocol example presented in this chapter also
