Biomedical Engineering Reference
In-Depth Information
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) for media
access.
Zigbee network topology defines three types of nodes: end-devices, router
nodes and coordinator nodes. A Zigbee coordinator node initiates the network and
manages network resources. Zigbee router nodes enable multi-hop communication
between the devices in a network. Zigbee's end-devices communicate with parent
nodes (router nodes or coordinator nodes) and operate with minimal functionality
in order to reduce the power consumption.
The Zigbee Alliance acts as the main body that provides application profiles for
Zigbee based applications. Zigbee based healthcare applications are intended to be
used in non-invasive healthcare platforms. MICAZ by Crossbow [
13
]isan
example of a commercial hardware platform that supports Zigbee communication.
Zigbee technology has several drawbacks for healthcare applications. It oper-
ates in the 2.4 GHz unlicensed industrial, scientific and medical (ISM) band
alongside with WLANs and Bluetooth making the 2.4 GHz band more crowded.
The power consumption of a Zigbee based sensor node is considerably high. For
example, the Chipcon IC (CC2420), which is a commercially available transceiver
has a current consumption of 17.4 mA in transmit mode and 19.7 mA in receive
mode [
14
].
1.2.2 Wireless Local Area Networks
Wireless Local Area Networks (WLAN) operate based on the physical and MAC
layer protocols developed in the IEEE 802.11 standard. Different versions of the
IEEE 802.11 standards use different physical layer communication mechanisms.
For example, the IEEE 802.11 g standard uses Orthogonal Frequency Division
Multiplexing (OFDM) while the IEEE 802.11b standard uses Direct Sequence
Spread Spectrum (DSSS) for physical layer communication. Even though WLAN
standards are able to cater for the high data rate requirement of WBAN applica-
tions, it is rarely used in WBAN applications because of its large power
consumption. For example, the most recent implementations of WLAN trans-
mitters consume around 82 mW of power [
15
].
1.2.3 Medical Implant Communication Services
Medical Implant Communication Services (MICS) band uses the 401-406 MHz
frequency band allocated by the Federal Communications Commission (FCC) in
order to transmit data from an implanted device to an outside controller [
16
]. Ten
channels with 300 kHz bandwidth are allocated for communication within this
band. The transmit power of the communication devices that uses the MICS band
