Biomedical Engineering Reference
In-Depth Information
Fig. 6.19 Current
measurement test set up
Power supply
Oscilloscope
-
+
Sensor node
10
Ω
operation after receiving the acknowledgement packet for the data packet that is
transmitted during the super frame time slot.
It can be seen from the results that all the data communication scenarios
consume a peak current of approximately 16.5 mA. Sleep mode current con-
sumption for periodic sensor nodes is observed to be 0.3 mA. UWB transmission
consumes the most amount of current during a data communication cycle. Current
consumption of the UWB transmitter is mostly affected by the operation of high
frequency Voltage Controlled Oscillator (VCO) in the RF portion of the circuit.
However, due to the high data rate of UWB transmission, duration of data
transmission occupies only a small percentage of the super frame duration
resulting in low energy consumption. This presents a unique advantage of the
UWB technology over other technologies in terms of energy saving. Periodic
sensor nodes largely benefit from this duty-cycled transmission since a large
amount of data can be accumulated over a long time before sending at a high data
rate. Furthermore, dual-band MAC protocol ensures that UWB sensor nodes are
transmitting at the optimum PPB value for a given distance. For example, UWB
transmitter of a particular continuous sensor node located at a separation distance
of 0.2 m transmits data at 20 PPB rather than transmitting at the maximum
allowable value of 100 PPB. This results in an energy saving of approximately
5 % for that particular distance. This energy saving increases to a large value over
the long life cycle of a WBAN sensor node. Use of a narrowband receiver further
enhances the power savings of a dual-band sensor node. An equivalent UWB
receiver has a power consumption that is several times larger than a narrowband
receiver [
11
-
13
]. Hence, use of a narrowband receiver in the sensor node pre-
sented in
Chap. 5
increases its lifetime by several times.
Table
6.2
depicts the average power and energy consumption of major sections
of the sensor node that are related to data communication scenarios shown in
Fig.
6.20
. Power is averaged over one transmission cycle. For example, trans-
mission cycle for a continuous sensor node is considered to be the duration of one
super frame (1 ms) and transmission cycle for a period sensor node is considered
to be the duration between two consecutive transmissions (10 s for this particular
experiment). Table
6.2
also show the energy consumption per useful data bit
transmitted using the UWB transmitter that can be obtained using (
6.2
).
¼
I
TX
ðÞ
V
s
ðÞ
T
TX
ðÞ
B
TX
J
bit
E
bit
ð
6
:
2
Þ
