Route discovery schemes in Mobile Ad hoc Networks with variable-range transmission power
Abstract
Broadcasting in MANETs is important for route discovery but consumes significant
amounts of power that is difficult to renew for devices that rely heavily on batteries.
Most existing routing protocols make use of a broadcast scheme known as simple
flooding. In such an on-demand routing protocol (e.g. AODV) the source node
originates a Route Request (RREQ) packet that is blindly rebroadcast via neighbouring nodes to all nodes in the network. Simple flooding leads to serious redundancy, together with contention, and collisions, which is often called the broadcast
storm problem. This thesis proposes two improvement strategies: topology control
(adjusting transmission power) and reduced retransmissions (reducing redundant rebroadcasts) to reduce energy consumption. For energy efficient route discovery the
main idea is to reduce the energy consumed per broadcast during route discovery.
An Energy Efficient Adaptive Forwarding Algorithm (called EEAFA) is proposed
to reduce the impact of RREQ packet flooding in on-demand routing protocols. The
algorithm operates in two phases: 1) Topology construction phase, which establishes
a more scalable and energy efficient network structure where nodes can adjust their
transmission power range dynamically, based on their local density. 2) A Forwarding Node Determination phase, that utilises network information provided by the
constructed topology, where nodes independently decide to forward a RREQ packet
or not without relying on GPS or any distance calculations.
A further Enhanced EEAFA (called E-EEAFA) algorithm is also proposed, which
combines two techniques: graph colouring and sectoring techniques. Graph colouring increases awareness at network nodes to improve the determination of a forwarding node, while the sectoring technique divides neighbours into different forwarding
sectors. This helps to reduce overlap between forwarding nodes and select suitable
nodes in each sector to forward RREQ packets. These techniques are employed in
a distributed manner and collaborate to reduce the number of forwarding nodes,
which thus reduces the volume of RREQ packets populating the network. These algorithms have been validated as effective by NS2 simulation studies that are detailed
in the thesis.