Wireless Network Design: Optimization Models and Solution ...

200 Khaldoun Al Agha and Steven Martin
Thus, delivering packets to a specific destination becomes a complex task due to
frequent and unpredictable topology changes.
The development of wireless ad hoc networks was initially motivated by military
applications, but nowadays, these networks are involved in many civil applications.
Therefore, these networks have to offer differentiated services, according to the application’s
requirements. This also implies admission control mechanisms. All these
topics have constituted hot research issues for the last decade. Obviously, solutions
leading to single-hop and multi-hop ad hoc networks are complex. They are all
the more complex when considering specific problems such as connectivity, security,
quality of service, energy consumption, and routing optimization. Indeed, not
only do ad hoc networks inherit the classical problems of wireless networks (e.g.
air medium propagation, unreliability, and hidden nodes), but also generate new
problems and complexities (e.g. autonomy, lack of infrastructure, dynamicity, and
scalability).
The remainder of this chapter is structured as follows. First, in Section 9.2, we
present routing issues, the constraints to take into account and the characteristics
of routing protocols. Then, we describe in Section 9.3 the two main link layer solutions
which enable single-hop ad hoc networks: the IEEE 802.11 standard and
the Bluetooth specification. In Section 9.4, the existing ad hoc routing protocols
are presented: ad hoc on-demand distance vector (AODV), dynamic source routing
(DSR), optimized link state routing (OLSR), and topology broadcast based on
reverse path forwarding (TBRPF). Finally, in Section 9.5 we present several methods
that provide quality of service (QoS) in mobile ad hoc networks: flexible QoS
model for MANETs (FQMM), core extraction distributed ad hoc routing (CEDAR),
ticket based probing (TBP), INSIGNIA, stateless wireless ad hoc network (SWAN),
and QoS for OLSR (QOLSR). Section 9.6 concludes the chapter.
9.2 What is Routing?
The main idea of an ad hoc network is that each wireless node can communicate
directly with any other wireless node, without the use of any existing network infrastructure.
Thus, the architecture is totally decentralized. Such networks are limited
by the fact that each wireless node has to be within the transmission range of all
the others; this leads to small networks as illustrated in Figure 9.1. The main problems
in ad hoc networks are how to transmit in, and share ,the air medium. There
exist two major link layer technologies used in ad hoc networks: the IEEE 802.11
standard and the Bluetooth specifications (see Section 9.3).
The architecture of an ad hoc network applies to small networks, due to the limited
transmission range of wireless network interfaces. As shown in Figure 9.1, extending
connectivity to a larger area requires a multi-hop ad hoc network architecture
in which each node assumes the role of a router and relays packets toward their
final destinations. Thus, network nodes cooperate to forward packets for each other