Database Reference
In-Depth Information
3.2 Active and Passive RFID Sensor Networks
The major limitation of the basic RFID sensor technology is that it
does not enable detailed sensing information. However, a number of
recent methods have been proposed to incorporate sensing into RFID
capabilities. One possibility is to use an onboard battery [106, 107]
in order to transmit more detailed sensing information about the en-
vironment. This is referred to as an
active
RFID tag. Of course, the
major limitation of such an approach is that the life-time of the tag is
limited by the battery. If a large number of objects are being tracked
at given time, then it is not practical to replace the battery or tag on
such a basis. Nevertheless, a significant amount of smart object tech-
nology is constructed with this approach. The major challenge from the
data-centric perspective is to clean or impute the missing data from the
underlying collection.
Recently, a number of efforts have focussed on the creating the abil-
ity to perform the sensing with
passive
RFID tags. Recently, a number
of efforts in this direction [22, 121] are designed to sense more detailed
information with the use of passive tags. The major challenge of this
approach is that the typical
range
at which the reader must be placed to
the tag is even smaller than the basic RFID technology, and may some-
times be less than three meters. This could lead to even more challenges
in terms of the dropped readings in a wide variety of application scenar-
ios. On the other hand, since the tag is passive, there are no limitations
on the life time because of battery-power consumption.
3.3 Wireless Sensor Networks
A possible solution is to use conventional wireless sensing technology
for building the internet of things. One, some, or all nodes in the sensor
network may function as gateways to the internet. The major advantage
is that peer-to-peer communications among the nodes are possible with
this kind of approach. Of course, this kind of approach is significantly
more expensive in large-scale applications and is limited by the battery
life. The battery-life would be further limited by the fact, that most
IP protocols cannot accommodate the sleep modes required by sensor
motes in order to conserve battery life. Since the network connectivity
of the internet of things is based on the IP protocols, this would require
the sensor devices to be on constantly. This would turn out to be a very
significant challenge in terms of battery life. The energy requirements
can reduced by a variety of methods such as lower sampling or trans-
mission rates, but this can impact the timeliness and quality of the data
available for the underlying applications. Wireless sensor networks also
