Biomedical Engineering Reference
In-Depth Information
•
Unlike the sensor nodes, the gateway node is allowed to have higher processing
power and battery power.
•
Communication is mostly one directional from the sensor nodes to the gateway.
Communication from the gateway node to the sensor nodes consist mainly of
network information and feedback.
A WBAN differs from a wireless sensor network (WSN) because of its specific
requirements. Differences between a WBAN and a more generic WSN are listed in
Table
1
.
Ultra-wideband (UWB) is defined as signals that have a fractional bandwidth
larger than 0.2 or at least 500 MHz. It is allowed to operate in the 0-960 MHz and
3.1-10 GHz bands; however, the effective isotopic radiated power (EIRP) must be
kept below
41.3 dBm/MHz [
4
]. UWB technology inherits several key properties
that make it a strong candidate for WBAN applications. These properties are briefly
discussed below:
−
1. Low power consumption of UWB transmitters
WBAN devices are considered as battery-powered devices; hence, the power
consumption of the data transmission devices involved in the WBAN should be
kept at a minimum in order to elongate the battery life of the devices. This is
very critical especially for implantable applications of WBANs, since replacing
a device or a battery will involve invasive surgery.
UWB transmitters use discrete pulses in order to transmit data [
5
,
6
], whereas
the traditional narrowband transmitters use data modulated continuous wave sig-
nals for wireless transmission [
7
]. Because of the discrete pulse transmission, a
significant portion of the data transmission time for the UWB transmitters con-
sists of a transmitter silent period, where the electronic components involved in
pulse generation can be operated at the low power mode. In contrast, traditional
narrowband transmitters operate continuously throughout the data transmission
period for most of the modulation schemes. This difference in the data mapping
principal results in a significant difference in the power consumption between the
former and the latter for longer periods of operation.
The implementation of an UWB transmitter involves very few radio frequency
(RF) components compared with the continuous wave transmitters. In fact, all
digital realizations of the UWB transmitters are achievable with the aid of state
of the art complementary metal-oxide semiconductor (CMOS) technology [
5
,
8
].
In contrast, traditional narrowband transmitters utilize power-consuming RF and
analog components, such as RF power amplifiers (PA) and analog phase-locked
loops (PLL), extensively because of the nature of the signal generation [
9
].
Furthermore, because of the possibility of direct mapping of the data into the
UWB pulses, complex modulation schemes are not required for UWB transmit-
ters. This further reduces the data processing requirement at the transmitter end
for UWB communication devices. This feature enhances the achievable power
savings of the UWB transmitters. Hence, the UWB transmitters hold a signifi-
cant advantage over the traditional narrowband transmitters for power-intensive
WBAN applications.
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