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1.7.3 Communication Media
A huge part of energy consumption is dependent on the medium of communication.
Since WSN uses radio-frequency (RF) communication, a great deal of effort has gone
into modeling the wireless channel so that it can help in characterizing the behavior of
WSN. Furthermore, multipath fading adds new complexities to transmission of wire-
less data in WSN. Research suggests that the radio irregularity model (RIM) is more
applicable than disc or spherical propagation models.
1.7.4 Integrated Circuit (IC) Technology
The use of custom-designed ICs rather than commercial ICs for WSN has greatly
reduced the consumption of battery power and has increased the lifetimes of the sensor
nodes. Furthermore, with advances in miniaturization technology, the size of the sen-
sor nodes has been reduced drastically and scalability has increased. However, integra-
tion of node supply voltages with custom ICs is still an open research problem (Cook
et al. 2006).
1.8 The Routing Problem in WSN
Routing in sensor networks has been very complex and challenging due to their intrin-
sic characteristics that differentiate them from other legacy wireless networks. First and
foremost, the assignment of a global addressing scheme is not possible due to the usage
of a relatively large number of sensor nodes. Furthermore, the ad-hoc, decentralized
nature of WSN compels the nodes to self-organize themselves to form a connected
network. Although routing in WSN has been more data-centric as opposed to address-
centric, it does raise serious security issues concerning authentication of sensor nodes
in a data-centric networking model. Second, the acceptance of a data-centric model
requires an efficient data aggregation model (discussed in Section 1.9.3) to reduce
redundancy and retransmission of packets. In addition, the resource-constrained
nature of WSN requires new energy-aware routing schemes. Some of the challenges
include the following.
• Routing protocols in WSN should aim to reduce the energy consumed per
packet. However, one of the major challenges is the uneven distribution of sensor
nodes. Due to the uneven topology, some intermediate nodes may expend more
energy when transmitting packets. In addition, if nodes are along an active rout-
ing path, the energy depletion rate will be higher than for other nodes. Therefore,
choosing an active routing path should consider the power levels of each node in
the network on a time basis.
• Proposing a global addressing scheme in a WSN network is very challenging,
due to the relatively large number of sensor nodes. In addition, IP headers can be
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