1.Coverage and connectivity issues in wireless sensor networks: A survey

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21 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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1.

Coverage and connectivity issues in wireless sensor networks: A survey


Amitabha Ghosh,

Sajal K. Das



Description:
-


I only read some basic contents of this paper, such as:



Introduction



Coverage and
connectivity



Preliminaries



Coverage based on exposure



Summary
:
-


Coverage and connectivity

together can be treated as a measure of quality

of service in a sensor network; it tells us how well each point

in the region

is covered and
h
ow accurate is the information gathered by the nodes.

T
hree types of coverage have been

defined
:



Blanket Coverage

to achieve a static arrangement of nodes that maximizes the
detection rate of targets appearing in the sensing

eld,



Barrier Coverage

to achieve a static arrangement of nodes that minimizes the
probability of undetected intrusion through the barrier,



Sweep Coverage


to move a number of nodes across a sensing field, such that it
addresses a specified balance between
maximizing the detection rate of events and
minimizing the number of missed detections per unit area.


Sensing Model:
-


Empirical observations suggest that the quality of sensing (sensitivity)
gradually attenuates with increasi
ng

distance. The sensitivity, S, of a sensor
s
i

at point P is
modeled as:

S (s
i
, P) = λ
/
d (s
i
, P)

α


Where

λ and α are sensor
-
dependent parameters and d (si, P) is the Euclidean distance
between the sensor and the

point.

I
n this model the sensing range for

each node is

confined
within a circular disk of radius R
s

, and is commonly referred to as the sensing radius.








In this model, a quantity R
u

is defined, such that when R
u

< R
s
, the probability that a node

would detect an object at a
distance less than or equal to (R
s

− R
u
) is one, and at a distance
greater than or equal

to (R
s

+ R
u
) is zero. In the interval (R
s

− R
u
, R
s

+ R
u
), an object will be
detected with probability p. The quantity

R
u

is a measure of uncertainty in sensor detectio
n.

Based on the probabilistic sensing model, the notion

of probabilistic coverage
of a point

P (
x
i
, y
i

) by a sensor si is defined as follows:

C
xi yi
(s
i

) =

0,

Rs + Ru ≤ d(s
i

, P)


e

ωaβ
,

Rs − Ru <
d (
s
i

, P) < Rs + Ru


1,

Rs − Ru ≥
d (
s
i

, P)


Where

a =
d (
s
i

, P)−(Rs − Ru), and ω and β are parameters that measure the detection
probabilities when an object

is within a certain
distance from a node.

Communication Model
:
-


Each node S
i

is able to communicate only up to

a certain threshold
distance from itself, called the communication radius, denoted by Rc
i
.
Nodes can have
different communication ranges depending on their transmission power levels. Two nodes
S
i and

S
j

are able to communicate with each other if the Euclidean distance between them is
less than or equal to the minimum

of their communication radii
, i.e.,

When

d(si , sj ) ≤ min

Rc
i
, Rc
j

.

Coverage based on exposure
:
-


Two kinds of viewpoints exist in formulating the coverage
p
roblem:


(1) Worst
-
case coverage,


(2) Best
-
case coverage.

In
the worst
-
case coverage, the problem is formulated with the goal to find a path through
the sensing region such

that, an object moving along that path has the least observability by
the nodes, and thus, the probability of detecting the

moving object is mini
mum.

I
n the best
-
case coverage problem formulation, the goal is to find a path that has the
highest observability, and

therefore, an object moving along such a path will be most
probable to be detected.

















2.

The Coverage Problem in a Wireless
Sensor Network:


Chi
-
Fu
Huang, Yu
-
Chee Tseng



Summary:


T
he coverage problem, reflects how well a sensor network is monitored or
tracked

by sensors. T
his paper, f
ormulate this problem as a deci
sion problem, whose
goal is to determine
whether every point in

the service area of the sensor netwo
rk is
covered by at least k sen
sors, where k is a predefined value. The sensing ranges of
sensors

can be unit disks or non
-
unit disks.

This
present polynomial
-
time

algorithm, in
terms of the number

of sensors.

Applications of

the result include:

(i)

positioning applications,

(ii)

situations which

require stronger environmental monitoring capability,

(iii)

Scenarios

which impose more stringent fault
-
tolerant capability.

T
his paper, have proposed solutions to two v
ersions of the

coverage problem,
namely k
-
UC

(Unit
-
disk
-
Coverage)

and k
-
NC

(Non
-
unit
-
disk
-
Coverage)
, in a wireless
sensor

network.
It

model the coverage problem as a decision problem,

whose goal is
to determine whether e
ach location of the target sens
ing a
rea is sufficiently covered
or not. Rather than determining

the level of coverage of each location, our solutions
are based on

checking the perimeter of each sensor’s sensing range. Although

this
r
scheme

can give an exact answer in O(nd log d) time.













3.

Coverage Problems in Wireless Ad
-
hoc Sensor Networks :


Seapahn Meguerdichian, Farinaz Koushanfar, Miodrag Potkonjak, Mani B.
Srivastava


Summary:


This paper,
address one of the fundamental problems, namely coverage.
Coverage in general, answers the questions about quality of service (surveillance)
that can be provided by a particular sensor network.

It

defines

the coverage problem from several points of view
i
ncluding:

Deterministic
, statistical, worst and best
case

and present examples in each domain.
By combining computational geometry and graph theoretic techniques, specifically
the Voronoi diagram and graph search
algorithms,

it

establishes

-

optimal polyno
mial
time worst and average case algorithm for coverage calculation.

In most sensor networks, two seemingly contradictory, yet related viewpoints of
coverage exist:
worst and
best case coverage
.

In worst
-
case coverage, attempts are made to quantify the
quality of service by
finding areas of lower observability from senso
r nodes and detecting breach re
gions.


In best
-
case cov
erage, finding areas of high ob
servability from sensors and
identifying the best support and guidance regions are of primary concern
.























4.

Energy
-
aware Node Placement in Wireless Sensor Networks:


Peng Cheng, Chen
-
Nee Chuah , Xin Liu



Summary:


One of the main design issues for wireless sensor

networks is the
sensor
placement problem. T
his paper,

formulate a constrained multivariable nonlinear
programming problem to determine both the locations of the sensor nodes and

data transmission pattern.

The two objectives studied in the paper are to maximize the network lifetime and to
minimize the
application
-
specific total cost, given a finite number of sensor/

aggre
-
gation nodes in a region with certain coverage requirement.

In this paper, we will examine many
-
to
-
one wireless sensor networks, where
information collected from all nodes is
aggrega
ted to a sink node
or fusion center.


Nodes closer to the sink node have heavier traffic load, since they not only collect
data within their sensing range but relay data for nodes further away as well.


Such an unbalanced traffic load introduces an unev
en power consumption
d
istribution among different sensor nodes.

Since traffic load and power
c
onsumption of each node are location
-
dependent, the
lifetime of a sensor network can be limited by those nodes with heavier traffic load
and th
us greater power co
nsumption.
Hence, node placement schemes will have
considerable impact on the lifetime of the whole sensor network.

The

contributions are threefold.


First, it

formulate a constrained multivariable nonlinear programming problem to

determine

both the locations of the nodes and the data

transmission pattern
considering two objectives: maximize the network lifetime and minimize the
application
-
specific total cost, given a finite number of sensor/aggregation nodes

in a geographical coverage.



Second, we present two optimal placement strategies, together with performance
bounds, for linear networks, i.e., sensors deployed along a straight line.

Third, after exploring and understanding the fundamentals of a linear network,
it

extends the resu
lts to a more sophisticated planar network.






5.

Coverage planning of Wireless Sensors for Mobile Target Detection:


Edoardo Amaldi, Antonio Capone, Matteo Cesana, Ilario Filippini

Politecnico di Milano, Italy



Summary:


This paper
proposes

an optimization framework for selecting the positions
of wireless sensors to detect mob
ile targets travers
ing a given area.

T
he main contributions of this paper are the

following:


1)
An

optimization approach to the planning of

sensor positions wh
ere
coverage
quality, defined accord
ing to the concept of exposure, depends on the Euclidean

distance from the intruder;

2)
Optimal

solution of different

planning problem versions based on MILP
f
ormulations;

3) An

efficient

heuristic algorithm that can be used to solve

large size instances in
reasonable time.


This paper

propose
s

and investigates two WSN

planning problems.

In the first one, sensors must be positioned in order to maximi
ze the exposure of the
least ex
posed pat
h, subject to a budge
t on the installation cost (num
ber of sensors).
In the se
cond one, sensors have to be po
sitioned so as to minimize the installation
cost, provided

that the exposure of the least
-
exposed path is above a given


threshold.

C
overage
quality depends on the

distance from sensors and is measured by the path
exposure,

which quantifies the capability of the network to detecting

a mobile object
moving along a given path.















6.

Mobility Improves Coverage of Sensor Networks

:


Benyuan
Liu
,
Peter Brass
,
Olivier Dousse
,
Philippe Nain
,
Don Towsley



Summary:


In this

paper, we study the dynamic aspects of the coverage of a

mobile
sensor network that depend on the process of sensor

movement. As time goes by, a
position is m
ore likely to be

covered; targets that might never be detected in a
stationary

sensor network can now be detected by moving sensors.


The main contributions of our work are:

First, we characterize the fraction of the area covered by

sensors for a randomly
-
deployed stationary sensor network.

This characterization shows how the covered
area depends

on the density and sensing characteristics of the sensors.

It
then
considers

a random mobility model for sensors

and
studies

the effect of
sensor mobility on variou
s aspects of

network coverage.

W
e study the detection time of an intruder, which is defined

to be the time elapsed
before the intruder is first detected.

For mobile intruders, the detection time
depends on both

the sensor and intruder mobility strategies.

For a given sensor mobility
behaviour
, we

assume that an intruder can choose its
mobility strategy so

as to maximize its detecti
on time (its lifetime before be
ing
d
etected).

On the other hand, sensors choose a mobility

strategy that minimizes th
e maximum
detection time result
ing from the intruder’s mobility strategy.

This paper

proves

that the

optimal sensor mobility strategy is for each sensor to
c
hoose

its direction uniformly
at random. The corresponding in
truder mobility
strategy is to remain stationar
y in order to

maximize the time before it is detected.