Mobility Aspects in WSN - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 118

The presented sensor self-deployment approach is advantageous because it
allows nodes to use only their local knowledge to make their deployment decision.
It does not require centralized control and localization. Possible weaknesses which
can be enumerated include coverage holes near the obstacles and frequent topology
changes (if nodes failures are often, thus causing frequent requirements for nodes
movements). It is computationally expensive and assumes that each node can sense
the exact relative range and bearing of its neighbors.
A similar idea with a different approach is presented in [ 20 ], where the sensor
locations are determined based on a virtual force assumed to exist among sensors
and between the sensors and obstacles in the field. Each sensor locally calculates
the sum of the vectors (representing relative positions) of neighboring nodes acting
it and moves according to the movement vector thus computed.
In the so-called virtual force -based mobile sensor deployment algorithm (VFA),
there is a powerful cluster head (CH) which executes the algorithm. The CH com-
municates with all the sensors, collects sensor position information, and calculates
forces and desired position for each sensor. In VFA, the distance between two adja-
cent nodes, when all nodes are evenly distributed, is defined as a threshold to distin-
guish attractive or repulsive force between the nodes. The total force on a node will
be the sum of all the forces given by other sensors together with obstacles and
preferential coverage in the area (Fig. 6.3 , Eq. 6.3). In terms of forces, the sensor nodes
are subject to three types of forces: repulsive forces due to the obstacles ( re F ),
attractive forces from the areas with pure coverage ( att F ), and forces (either attrac-
tive or repulsive) from the other sensor nodes depending on their distance and
orientation (

F ).

sensor

( )

k

∑

F F FF
=≠

= ++ (6.3)

i sensor rep attr

ij i i

j ji 1,

Among the virtual force and potential field-based approaches, a distributed
self-deployment algorithm (DSSA) has been proposed in [ 21 ]. The objective of

Y

Frep

Sb

Sa

X

Sa

Sb

Sd

attractive force

Fa total

Sa

Sb Fattr

Sc

repulsive force

Fig. 6.3 Attractive and repulsive virtual forces