Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 44

Ad Hoc network routing protocols are difficult to design in general. There are two
main reasons for that; the highly dynamic nature of the Ad Hoc networks due to high
mobility of the nodes, and the need to operate efficiently with limited resources such
as network bandwidth and limited memory and battery power of the individual
nodes in the network.
Moreover, routing protocols in Ad Hoc networks, unlike static networks, do not
scale well due to frequently changing network topology, lack of predefined infra-
structure like routers, peer-to-peer mode of communication, and limited radio com-
munication range [ 1 ].
For these reasons, many routing protocols that are compatible with the character-
istics of Ad Hoc networks have been proposed. In general, they can be divided into
two main categories: topology-based and position-based. Topology-based routing
protocols use information about links that exist in the network to perform packet
forwarding. They are, in turn, divided into three categories: proactive, reactive, and
hybrid (hierarchical) protocols.
Proactive routing protocols periodically broadcast control messages in an attempt
to have each node always know a current route to all destinations, and remove local
routing entries if they time out. We observed that proactive routing protocols are less
suitable for Ad Hoc wireless networks because they constantly consume power
throughout the network, regardless of the presence of network activity. Also they are
not designed to track topology changes occurring at a high rate.
On the other hand, reactive routing protocols are deemed more appropriate for
wireless environments because they initiate a route discovery process only when
data packets need to be routed. Many Ad Hoc routing protocols that use reactive
route determination have been developed such as Ad Hoc On-demand Distance
Vector (AODV) [ 2 ] protocol. One advantage of reactive routing protocols is that no
periodic routing packets are required. However, they may have poor performance
in terms of control overhead in networks with high mobility and heavy traffic loads.
Scalability is said to be another disadvantage because they rely on blind broadcasts
to discover routes.
As seen, proactive routing uses excess bandwidth to maintain routing informa-
tion, while reactive routing involves long route request delays. Reactive routing
also inefficiently floods the entire network for route determination. Hybrid routing
protocols aim to address these problems by combining the best properties of both
approaches. The disadvantage of ZRP is that for large values of routing zone the
protocol can behave like a pure proactive protocol, while for small values it behaves
like a reactive protocol [ 3 ]. In general, topology-based are considered not to scale
in networks with more than several hundred nodes [ 4 ].
In recent developments, position-based routing protocols exhibit better scalabil-
ity, performance, and robustness against frequent topological changes [ 1, 4 ].
Position-based routing protocols use the geographical position of nodes to make
routing decisions, which results in improving efficiency and performance. These
protocols require that a node be able to obtain its own geographical position and the
geographical position of the destination. Generally, this information is obtained via
Global Positioning System (GPS) and location services [ 5 ]. The routing decision at