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Stephanie Kinsella
GEAR: Geographical and Energy Aware Routing
Definition
GEAR stands for Geographical and Energy Aware Routing. GEAR uses
energy aware and geographically informed neighbor selection to route a packet
towards the targeted region. Within that region, GEAR uses a recursive geographic
forwarding technique to disseminate the packet.
Summary
Each node in a sensor network may be comprised of one or more sensors, a low power
radio, portable power supply, and possibly a Global Positioning System. The most
important feature of networks such as these, is that their nodes are unattended and
have limited and non-replenishable energy sources, which makes energy efficiency an
important design consideration. In GEAR, the process of forwarding a packet to all
the nodes in the target region consists of two stages. The first is forwarding the
packets towards the target region and the second is disseminating the packet within
the region. This algorithm assumed that each query packet has a specified target
region, each node knows its own location and remaining energy level and it’s
neighbor’s locations and remaining energy levels and that the link between is bidirectional. Whenever a node receives a packet, it will pick the next hop among the
neighbors that are closer to destination. Once the packet is inside the target region,
the packets can be flooded inside the region. Flooding is expensive in terms of energy
consumption; therefore, GEAR uses a Recursive Geographic Forwarding
approach to disseminate the packet inside the target region. Under some conditions,
the geographically direct path is more energy efficient and as a result prolongs
network lifetime over the energy aware system. Pure geographic mode is used when
either the number of hops traversed crossed a certain threshold, after a packet
reaches a node whose neighbors are heavily depleted, or when nodes are near the
target region.
Performance Comparison
GEAR exhibits noticeably longer network lifetime than non-energy-aware
geographic routing algorithms. The most important performance measure is increased
network lifetime due to energy awareness. This algorithm is often compared to
Greedy Perimeter Stateless Routing, known as GPSR. Since the original GPSR
does not handle routing to a region, there is an augmented GPSR with the recursive
forwarding protocol to route packets to a region. With random/uniform traffic
distribution, the algorithm successfully delivers 25-35% more packets than GPSR.
One reason that GEAR prolongs network lifetime compared to GPSR, is that
GPSR tends to concentrate traffic on the perimeter when it routes around holes,
which burns out nodes on the perimeter faster. GEAR is roughly 50% more efficient
than its pure geographical variant and approximately 70% more efficient then GPSR.
Under non-uniform traffic, GEAR delivers 70-80% more packets than GPSR.
GEAR displays more gain in non-uniform traffic situations than in uniform traffic.
When traffic sources are clustered together, GEAR’s energy balancing efforts have
the most benefit. Under non-uniform energy distribution, where the nodes in the
target region have a higher initial energy value than others, the results of GEAR are
even greater. Results show that GEAR delivers 125% more packets than GPSR.