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Complex Networks by Kayhan Erciyes

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Chapter 13
Ad hoc Wireless Networks
13.1 Introduction
A wireless network consists of computing nodes which communicate using wire-
less communication channels. Wireless networks can be formed as in frastructured
or ad hoc. A static wired backbone usually consisting of host computers provides
the communication in infra-structured networks whereas nodes of an ad hoc wire-
less network communicate using multi-hop packet transfers. Two important types of
ad hoc wireless networks are the mobile ad hoc networks (MANETs) and wireless
sensor networks (WSNs). There is no fixed infrastructure in a MANET as the nodes
in such a network change their positions dynamically. Nodes in a MANET commu-
nicate with their current immediate neighbors to transfer messages to destinations.
Figure 13.1 displays a MANET with host computers A,...H which communicate us-
ing wireless links. It can be seen that mobile hosts F and G have a more central
function than others as most of the message transfers between any nodes should pass
through them.
Routing is the process of determining the lowest cost paths between source nodes
and destination nodes in a computer network. Since the topology of a MANET
changes frequently, finding efficient routes dynamically is one of the main challenges
in these networks. Another challenge is the provision of access control to the shared
medium as concurrent accesses will result in collisions of packets and should be
avoided.
A WSN consists of hundreds and thousands of sensor nodes each equipped with
a battery and antenna to communicate with neighbors. These sensor nodes gather
data from the surrounding area and send this data to a special node called the sink,
which has better processing capabilities and performs further fine processing of the
data and may transfer it to a remote host computer for analysis. Figure 13.2 shows
the general structure of a sensor network where nodes send their data to the sink
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Complex Networks: An Algorithmic Perspective
A
D
E
F
G
C
B
Figure 13.1: A MANET example
SINK
DATA
CENTER
ANALYZING
Figure 13.2: A WSN example
using a spanning tree structure and the sink transfers the data to a data analyzing
center after initial processing. Different from a MANET, data transfer is oriented to-
ward the sink and routing of data packets to the sink in this manner is an important
issue in a WSN. Furthermore, limited lifetime of the on-board batteries necessitates
employment of energy efficient algorithms with low message complexities for rout-
ing and other tasks as message transfers are the main source of energy dissipation

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