Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 47

the shortest path and are robust against the failure of individual nodes and position
inaccuracy.
The third forwarding strategy is to form a hierarchy in order to scale to a large
number of mobile nodes. Some strategies combine nodes location and hierarchical
network structures by using the zone-based routing such as LABAR. Others use the
dominating set routing such as GRID. Some others, such as TERMINODES, present
a two-level hierarchy within them; if the destination is close to the sender (in num-
ber of hops), packets will be routed based on a proactive distance vector. Greedy
routing is used in long-distance routing; therefore, they have characteristics similar
to those of greedy forwarding.

4.3 Overview of Selected Position-Based Routing Protocols

In this section the selected protocols are described. For each protocol, we tried to
summarize its main objectives, how it works, and its advantages and disadvantages
compared to other protocols.

4.3.1 MFR

Some greedy position-based routing protocols, such as Most Forward within distance
R (MFR) [ 8 ], aim to minimize the number of hops by selecting the node with the
largest progress from the neighbors, where progress is defined as the projection of the
distance of the next hop from the sender on the straight line between the sender and
the destination [ 4, 7, 12 ]. In Fig. 4.2 , if the MFR is used the source S will choose the
node A as the next hop since it has the largest progress to the destination D.
As other greedy forwarding protocols, MFR has the shortcomings of either not
guaranteeing to find a path to the destination or finding a path which is much longer
than the shortest path. Moreover, nodes periodically should broadcast beacons to
announce their positions and enable other nodes maintain a one-hop neighbor table.

Fig. 4.2 MFR example