Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 61

When using a fixed transmission power, nodes may waste power by transmitting
with more power than is needed for correct reception. Hence, these new algorithms
use the idea of replacing the constant transmission power of the node with an
adjusted transmission power during neighbors' discovering and routing process
stages.
The first proposed algorithm is Power Adjusted Greedy algorithm (PAG); in this
algorithm all nodes use the low transmission range, which equals half of their maximum
transmission range, to discover their neighbors. This process is done periodically.
When a source needs to send a data packet to a specific destination the greedy routing
is started. If the packet is stuck at a node that does not have a neighbor that makes
progress to the destination, then the current node increases its transmission range by
a specific factor and runs neighbor nodes discovery step again. If the node does not
discover a new neighbor that makes progress to the destination, then the algorithm
fails, otherwise greedy routing continues.
PAG has a great advantage in terms of power saving. However, through simula-
tions authors discovered that it suffers from a low delivery rate if the network is very
sparse; thus, PAG:CFace(3) was proposed. It starts with PAG routing algorithm. If
the current node adjusts its transmission range and still stays in the local minimum
situation, then the algorithm changes to CFace(3). If CFace(3) fails to deliver the
message the algorithm fails. Their last algorithm is PAG:CFace(1):PAG. The only
difference between this algorithm and the second one is that instead of trying another
projective plane if the first projective plane fails, it returns immediately back to the
PAG algorithm.
Simulation results showed a significant improvement in the energy saving (up to
50%) compared with available power-aware routing algorithms. Moreover, the
second routing algorithm PAG:CFace(3) increases the delivery rate to around 100%
for both sparse and dense networks. Hence, the most important advantage of PAGs
is the great increase of the network lifetime while preserving the delivery rates.
On the other hand, using greedy forwarding and discovering the nodes' neighbors
using low transmission ranges will increase the probability of using paths that
are longer than the optimal path. Also the adjustment of transmission range and
the multiple switching among different algorithms, especially with the use of
CFace(3) that requires projection of nodes into the three planes may increase
processing overhead.

4.3.14 SPAAR

All the previously mentioned position-based routing protocols are vulnerable to some
attacks, as they focus on improving performance while disregarding security issues
[ 20 ]. In addition, most of them are not guaranteed to find the shortest path. In the past
few years, a limited work has been done to introduce some security issues to position-
based routing protocols. Examples of these are Secure Position Aided Ad Hoc Routing