Biomedical Engineering Reference
In-Depth Information
This is mainly due to higher BER of Scenario 2 compared to other scenarios over
this separation distance range. These results further highlight the importance of the
multiple PPB scheme in order to keep the sensor initialization delay at an
acceptable level.
6.7 Power Consumption of Dual-Band Sensor Nodes
in WBAN Operation
Power consumption is one of the important areas for battery powered WBAN
applications. Both wearable and implantable WBAN sensor nodes should be able
to operate with minimum intervention for longer periods. UWB transmitters are
inherently low power consuming compared to UWB receivers mainly due to its
low complexity circuit design. The sensor platform presented in
Chap. 5
avoids
the high complexity and power hungry UWB receiver by using a narrowband
receiver. Even further improvements in power consumption can be achieved by
proper design of the MAC protocol.
One of the main attributes of the MAC protocol design presented in this chapter
is that it uses the minimum PPB value that is achievable at a given time in order to
transmit data while maintaining the BER approximately at 10
-4
. Using the min-
imum PPB value for data transmission ensures that the duration of UWB data
transmission is kept at its optimum value throughout the data transmission cycle.
Duration of data transmission is one of the key factors that determine the energy
consumption of a MAC protocol. Hence, keeping the duration of data transmission
slot to an optimum value helps to optimize the power consumption of sensor
nodes.
The experimental setup shown in Fig.
6.19
is used in order to measure the
overall current consumption of the sensor nodes. A probe with low capacitance is
used for voltage measurement across the 10 X resistor and all the higher order
bypass capacitors are removed from sensor nodes in order to minimize the
capacitive effects on the measured waveforms.
Figure
6.20
depicts the overall current consumption of a periodic sensor node
that transmits at 100 PPB with a packet length of 50 bits and two continuous sensor
nodes that transmit at 20 and 100 PPB with a packet length of 100 bits. All the
sensor nodes transmit at a PRF of 100 MHz. Current consumption measurements
have been carried out over a period of 2 ms (i.e. two super frame durations).
Figure
6.20
also shows current consumption for different stages of a sensor start-
up period. Sensor nodes are programmed to send data packets with dummy pay-
load after the first beacon reception for the purpose of demonstrating the variation
of current consumption during a data communication period of the dual MAC
protocol. Narrowband receiver is continuously operated throughout the data
communication period for continuous sensor nodes in order to receive control
packets from the coordinator node. Periodic sensor nodes go into sleep mode
