Mobility Aspects in WSN - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 127

GRG is a combination of GA and a rotation which is applied in a node when its
GA movement is blocked. Rotation around PoI is performed in a counterclockwise
direction, and a node will stop rotating after it reaches a vertex when greedy move-
ment can resume (or when the rotation in the next hop is occupied, or else when it
returns to the starting vertex). The nodal rotation will form the final network in a
hexagon shape. The suspension and competition rules can be further implied.
The algorithms are localized self-deployment algorithms, and performance
analyses demonstrate that in a finite time they yield to a connected network with
full coverage. However, the results of analyses are achieved without taking into
consideration the possible obstacles in the sensor field.
Comparisons among the various strategies for coverage improvement are sum-
marized in Table 6.1 . The comparison is based on the goals and advantages vs.

Table 6.1 Comparison of different approaches for coverage improvement

Goals and
performances Algorithm Advantages Disadvantages

PFA Coverage

improvement
while
maintaining
k-connectivity

Scalability,
no need of
centralized
control and
localization

Computation expensive,
assumption that
every node knows the
position and bearing
of the other nodes

VFA Increasing coverage

after random
sensor deployment

Only local knowledge,
no need of
centralized control
and localization,
flexibility, negligible
computation time

Possible coverage holes
near the obstacles,
computation expensive

DSSA Maximizing coverage

and maintaining
uniformity

Distributed algorithm,
limits possible
oscillations

Requires location awareness,
obstacles are not
considered

VEC, VOR,
min-max

Reducing or eliminating
coverage holes

Distributed
algorithms, local
communications
and movements

Poor performances in
disconnected and
clustered networks

BIDP Coverage improvement

with distributed
allocation of
mobile nodes to the
coverage holes

Distributed protocol,
cost balance

Several nodes can move
towards same hole,
requires knowledge of
the nodes positions

PROXY Reducing energy

consumption and
load balancing,
while maintaining
coverage

One time movement,
multiple healing
avoidance

Requires location awareness,
bandwidth demanded,
high complexity for
implementation

Quorum based Reduction of the sensor

relocation time,
balance of the
energy consumption

Distributed algorithm,
relocation towards
failed nodes

Requires pre-knowledge of
the sensor field, message
overheads, replaces
sensors after failing
(continued)