Routing in ad hoc networks

The aim of ad hoc networks is to connect communicating entities (which may be mobile) outside any pre-existing infrastructure, within spontaneous networks. An intuitive and simple way of conceiving ad hoc networks is to consider them as the ultimate generalization of wireless networks, since they limit the role of fixed infrastructure to a minimum. This generalization is achieved by enhancing the connectivity capabilities of wireless LANs.

An ad hoc network must be able to be deployed on demand and to cover a wide range of practical situations. It must not be centralized, as this would limit the range of possible applications, and wireless technologies, which are inherently easier to implement, would be expected to take precedence. Finally, an ad hoc network must be a genuine network; it must not suffer from any strong limitation in terms of its coverage area. Consequently, an ad hoc network, which uses radio transmission technology as its preferred technology, must use the relaying technique to ensure the possible extension of its coverage area. Being spontaneous by nature, an ad hoc network is likely to include a large percentage of mobile nodes.

The ad hoc network can be seen as the ultimate generalization of the wireless network. The motivations for this are to be found among those wireless network applications that have not received a completely satisfactory response from this technology. If wireless networks can handle mobility in areas of limited coverage, ad hoc network applications will seek to generalize this mobility. The applications that will turn to ad hoc networks are naturally those that can't make do with restricted mobility, or that rely on an existing infrastructure. These applications naturally include military networks, but also emergency networks and temporary exhibition or event networks.

The military is a prime area for ad hoc networks. A tactical communications network must be able to be deployed on demand and operate without any pre-existing communications infrastructure. It must, of course, tolerate mobility; it must also remain stealthy, which forbids centralized systems with antennae on a high point. It must also be high-performance, since more and more information exchanged on the battlefield includes images, which entail high transmission costs in terms of volume. Many military programs in Europe use ad hoc network technology:

• the FÉLIN program (Fantassin à Équipement et Liaisons INtégrées), a DGA (Délégation Générale de l'Armement) program;

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