Biomedical Engineering Reference
In-Depth Information
Table 3.2 Commonly monitored medical parameters
Medical parameter
Transmit period
Sampling rate (samples/s)
Bits per sample
Data rate
WCE
Continuous
5 Mbps
ECG
Continuous
300
12
3.6 kbps
EEG
Continuous
200
12
2.4 kbps
Heart beat
Every 1 s
100 bps
Oxygen saturation
Every 1 s
100 bps
Blood pressure
Every 1 min
12 bps
Temperature
Every 1 min
12 bps
3.3.4 Super Frame Structure
A Beacon enabled super frame structure is considered for the UWB WBAN MAC
protocol. The network topology for the simulated system is developed based on a
simplified version of the IEEE 802.15.4/4a [
21
,
22
] beacon enabled star topology
with modifications added to make it better suited for low power IR-UWB trans-
mission. Beacon enabled mode provides the timeliness guarantees to the network.
Super frame structure depends on three major factors; the data rate and priority
requirements of the sensor nodes, duty cycle requirement, which itself depends on
the maximum power limitations and finally, the total number of active sensor
nodes in the network.
A set of commonly monitored physiological parameters are shown in Table
3.2
.
A WBAN consists of two types of sensor nodes depending on their data trans-
mission rate. WCE, ECG and EEG
2
are continuously transmitting sensors that
require high data transmission rate and high guarantee of delivery [
3
]. These
signals can be classified as critical parameters and the MAC protocol is designed to
prioritize the delivery of such data. Sensor nodes that transmit heart rate and blood
pressure are periodic sensors and do not require high data rate.
The super frame structure described in this section is divided into a Contention
Access Period (CAP) and a Contention Free Period (CFP). CFP offers Guaranteed
Time Slots (GTS) for the sensor nodes to transmit data. Continuously transmitting
sensor nodes are thus assigned with GTS to increase the reliability of the network.
Periodic sensor nodes contend for transmission during the CAP.
Data rates for the sensor nodes in the simulation are chosen in order to represent
the sensor nodes that require highest data rates from each type. This means, an
effective data rate of 5 Mbps is chosen for a continuous sensor node and it is
assumed that the periodic sensor nodes produce 100 bits every one second.
However, this 100-bit payload for a particular periodic sensor node is sent during
one time slot in the CAP to increase the efficiency of the MAC protocol.
2
These continuous medical signals are usually considered as crucial in hospital environments.
However classification of medical signals can easily be prioritised according to the individual
patient being monitored.
