Biomedical Engineering Reference
In-Depth Information
(SAR). Hence, transmit power control is important in wireless technologies used
for WBAN applications. Basic requirements of a WBAN are listed below [
7
,
8
];
• Support of scalable data rates
• Low power consumption.
• Small form factor.
• Controllable transmit power.
• Ability to prioritise data transmission of crucial signals.
• Secure data transmission.
• Coexistence with other wireless technologies.
• Ability to operate in multi user environments.
A typical WBAN uses a three- tier network structure as shown in Fig.
1.1
.
Sensor nodes and gateway nodes communicate using short range wireless com-
munication mechanisms. Gateway nodes can choose to communicate with a
coordinator node either via a short range wireless communication link or a long
range wireless communication link. A Coordinator node forwards data to the
internet where data can be transferred to a remote data base. Sensor nodes are
connected to a gateway node in a star topology, while several gateway nodes can
be connected to a coordinator node using the same topology. Sensor nodes are
always attached to the body as either implant devices or wearable devices.
Gateway nodes may not be attached to the body; hence, they are not power
restricted like sensor nodes. Gateway nodes can communicate with coordinator
nodes either using short range Wireless Personnel Area Networks (WPAN) or long
range Wireless Local Area Networks (WLAN). WPAN has a range of 10 m while
WLAN expands for more than 100 m.
WBANs are used in both medical and non-medical applications. Wireless
Electrocardiogram (ECG) monitoring systems and wireless neural recording sys-
tems are examples of medical applications that can be implemented using WBAN
techniques. WBANs can also be used for non-medical applications such as gaming
and smart home control [
9
]. Several key components can be identified in a WBAN
system for healthcare monitoring applications. Sensor nodes are either implantable
or on-body devices that transmit vital physiological information, such as ECG,
Electroencephalogram (EEG) and body temperature to an outside node. A
coordinator node or a router node is used to collect and route the information sent
by a sensor node and forward this information to a computer based application for
interpretation. Figure
1.2
illustrates the key components of a WBAN.
A WBAN used for healthcare monitoring inherits several key requirements. An
implanted or on-body sensor node is battery powered. Especially in the implant-
able case, human intervention in replacing the batteries should be kept at a
minimum level, since it might involve surgical procedures. Hence a WBAN sensor
node should consume low power. Low power transmission of signals limits the
communication range (usually 0.1-2 m). As a result, an optimized low complexity
MAC protocol should be used in WBANs so that it would enhance the low power
operation of the sensor node.
