<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
(	O
WSNs	B-Architecture
)	O
refer	O
to	O
networks	O
of	O
spatially	O
dispersed	O
and	O
dedicated	O
sensors	O
that	O
monitor	O
and	O
record	O
the	O
physical	O
conditions	O
of	O
the	O
environment	O
and	O
forward	O
the	O
collected	O
data	O
to	O
a	O
central	O
location	O
.	O
</s>
<s>
WSNs	B-Architecture
can	O
measure	O
environmental	O
conditions	O
such	O
as	O
temperature	O
,	O
sound	O
,	O
pollution	O
levels	O
,	O
humidity	O
and	O
wind	O
.	O
</s>
<s>
These	O
are	O
similar	O
to	O
wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
networks	I-General_Concept
in	O
the	O
sense	O
that	O
they	O
rely	O
on	O
wireless	O
connectivity	O
and	O
spontaneous	O
formation	O
of	O
networks	O
so	O
that	O
sensor	O
data	O
can	O
be	O
transported	O
wirelessly	O
.	O
</s>
<s>
WSNs	B-Architecture
monitor	O
physical	O
conditions	O
,	O
such	O
as	O
temperature	O
,	O
sound	O
,	O
and	O
pressure	O
.	O
</s>
<s>
A	O
WSN	B-Architecture
is	O
built	O
of	O
"	O
nodes	O
"	O
–	O
from	O
a	O
few	O
to	O
hundreds	O
or	O
thousands	O
,	O
where	O
each	O
node	O
is	O
connected	O
to	O
other	O
sensors	O
.	O
</s>
<s>
Each	O
such	O
node	O
typically	O
has	O
several	O
parts	O
:	O
a	O
radio	O
transceiver	O
with	O
an	O
internal	O
antenna	O
or	O
connection	O
to	O
an	O
external	O
antenna	O
,	O
a	O
microcontroller	B-Architecture
,	O
an	O
electronic	O
circuit	O
for	O
interfacing	O
with	O
the	O
sensors	O
and	O
an	O
energy	O
source	O
,	O
usually	O
a	O
battery	O
or	O
an	O
embedded	B-Architecture
form	O
of	O
energy	O
harvesting	O
.	O
</s>
<s>
A	O
sensor	B-Device
node	I-Device
might	O
vary	O
in	O
size	O
from	O
a	O
shoebox	O
to	O
(	O
theoretically	O
)	O
a	O
grain	O
of	O
dust	O
,	O
although	O
microscopic	O
dimensions	O
have	O
yet	O
to	O
be	O
realized	O
.	O
</s>
<s>
Sensor	B-Device
node	I-Device
cost	O
is	O
similarly	O
variable	O
,	O
ranging	O
from	O
a	O
few	O
to	O
hundreds	O
of	O
dollars	O
,	O
depending	O
on	O
node	O
sophistication	O
.	O
</s>
<s>
The	O
topology	O
of	O
a	O
WSN	B-Architecture
can	O
vary	O
from	O
a	O
simple	O
star	B-Architecture
network	I-Architecture
to	O
an	O
advanced	O
multi-hop	B-General_Concept
wireless	O
mesh	O
network	O
.	O
</s>
<s>
Propagation	O
can	O
employ	O
routing	B-Protocol
or	O
flooding	B-Protocol
.	O
</s>
<s>
In	O
computer	B-General_Concept
science	I-General_Concept
and	O
telecommunications	O
,	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
are	O
an	O
active	O
research	O
area	O
supporting	O
many	O
workshops	O
and	O
conferences	O
,	O
including	O
International	O
Workshop	O
on	O
Embedded	B-Architecture
Networked	I-Architecture
Sensors	I-Architecture
(	O
EmNetS	O
)	O
,	O
IPSN	B-Device
,	O
SenSys	B-Application
,	O
MobiCom	O
and	O
EWSN	B-Device
.	O
</s>
<s>
As	O
of	O
2010	O
,	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
had	O
deployed	O
approximately	O
120million	O
remote	O
units	O
worldwide	O
.	O
</s>
<s>
Area	O
monitoring	O
is	O
a	O
common	O
application	O
of	O
WSNs	B-Architecture
.	O
</s>
<s>
In	O
area	O
monitoring	O
,	O
the	O
WSN	B-Architecture
is	O
deployed	O
over	O
a	O
region	O
where	O
some	O
phenomenon	O
is	O
to	O
be	O
monitored	O
.	O
</s>
<s>
There	O
are	O
several	O
types	O
of	O
sensor	B-Architecture
networks	I-Architecture
for	O
medical	O
applications	O
:	O
implanted	O
,	O
wearable	O
,	O
and	O
environment-embedded	O
.	O
</s>
<s>
Devices	O
embedded	B-Architecture
in	O
the	O
environment	O
track	O
the	O
physical	O
state	O
of	O
a	O
person	O
for	O
continuous	O
health	O
diagnosis	O
,	O
using	O
as	O
input	O
the	O
data	O
from	O
a	O
network	O
of	O
depth	B-Algorithm
cameras	I-Algorithm
,	O
a	O
sensing	O
floor	O
,	O
or	O
other	O
similar	O
devices	O
.	O
</s>
<s>
Especially	O
due	O
to	O
the	O
integration	O
of	O
sensor	B-Architecture
networks	I-Architecture
,	O
with	O
IoT	B-Operating_System
,	O
the	O
user	O
authentication	O
becomes	O
more	O
challenging	O
;	O
however	O
,	O
a	O
solution	O
is	O
presented	O
in	O
recent	O
work	O
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
have	O
been	O
used	O
to	O
monitor	O
various	O
species	O
and	O
habitats	O
,	O
beginning	O
with	O
the	O
Great	O
Duck	O
Island	O
Deployment	O
,	O
including	O
marmots	O
,	O
cane	O
toads	O
in	O
Australia	O
and	O
zebras	O
in	O
Kenya	O
.	O
</s>
<s>
For	O
research	O
purposes	O
,	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
have	O
been	O
deployed	O
to	O
monitor	O
the	O
concentration	O
of	O
dangerous	O
gases	O
for	O
citizens	O
(	O
e.g.	O
,	O
in	O
London	O
)	O
.	O
</s>
<s>
A	O
network	O
of	O
Sensor	B-Device
Nodes	I-Device
can	O
be	O
installed	O
in	O
a	O
forest	O
to	O
detect	O
when	O
a	O
fire	O
has	O
started	O
.	O
</s>
<s>
The	O
early	O
detection	O
is	O
crucial	O
for	O
a	O
successful	O
action	O
of	O
the	O
firefighters	O
;	O
thanks	O
to	O
Wireless	B-Architecture
Sensor	I-Architecture
Networks	I-Architecture
,	O
the	O
fire	O
brigade	O
will	O
be	O
able	O
to	O
know	O
when	O
a	O
fire	O
is	O
started	O
and	O
how	O
it	O
is	O
spreading	O
.	O
</s>
<s>
A	O
landslide	O
detection	O
system	O
makes	O
use	O
of	O
a	O
wireless	B-Architecture
sensor	I-Architecture
network	I-Architecture
to	O
detect	O
the	O
slight	O
movements	O
of	O
soil	O
and	O
changes	O
in	O
various	O
parameters	O
that	O
may	O
occur	O
before	O
or	O
during	O
a	O
landslide	O
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
can	O
be	O
effective	O
in	O
preventing	O
adverse	O
consequences	O
of	O
natural	O
disasters	O
,	O
like	O
floods	O
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
have	O
been	O
developed	O
for	O
machinery	O
condition-based	O
maintenance	O
(	O
CBM	O
)	O
as	O
they	O
offer	O
significant	O
cost	O
savings	O
and	O
enable	O
new	O
functionality	O
.	O
</s>
<s>
Wireless	B-Architecture
sensors	I-Architecture
can	O
be	O
placed	O
in	O
locations	O
difficult	O
or	O
impossible	O
to	O
reach	O
with	O
a	O
wired	O
system	O
,	O
such	O
as	O
rotating	O
machinery	O
and	O
untethered	O
vehicles	O
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
also	O
are	O
used	O
for	O
the	O
collection	O
of	O
data	O
for	O
monitoring	O
of	O
environmental	O
information	O
.	O
</s>
<s>
The	O
advantage	O
of	O
WSNs	B-Architecture
over	O
conventional	O
loggers	O
is	O
the	O
"	O
live	O
"	O
data	O
feed	O
that	O
is	O
possible	O
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
can	O
be	O
used	O
to	O
monitor	O
the	O
condition	O
of	O
civil	O
infrastructure	O
and	O
related	O
geo-physical	O
processes	O
close	O
to	O
real	O
time	O
,	O
and	O
over	O
long	O
periods	O
through	O
data	O
logging	O
,	O
using	O
appropriately	O
interfaced	O
sensors	O
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
are	O
used	O
to	O
monitor	O
wine	O
production	O
,	O
both	O
in	O
the	O
field	O
and	O
the	O
cellar	O
.	O
</s>
<s>
The	O
Wide	B-Architecture
Area	I-Architecture
Tracking	I-Architecture
System	I-Architecture
(	O
WATS	O
)	O
is	O
a	O
prototype	O
network	O
for	O
detecting	O
a	O
ground-based	O
nuclear	O
device	O
such	O
as	O
a	O
nuclear	O
"	O
briefcase	O
bomb.	O
"	O
</s>
<s>
Data	O
picked	O
up	O
by	O
the	O
sensors	O
undergoes	O
"	B-General_Concept
data	I-General_Concept
fusion	I-General_Concept
"	I-General_Concept
,	O
which	O
converts	O
the	O
information	O
into	O
easily	O
interpreted	O
forms	O
;	O
this	O
data	O
fusion	O
is	O
the	O
most	O
important	O
aspect	O
of	O
the	O
system	O
.	O
</s>
<s>
The	O
data	O
fusion	O
process	O
occurs	O
within	O
the	O
sensor	B-Architecture
network	I-Architecture
rather	O
than	O
at	O
a	O
centralized	O
computer	O
and	O
is	O
performed	O
by	O
a	O
specially	O
developed	O
algorithm	O
based	O
on	O
Bayesian	O
statistics	O
.	O
</s>
<s>
Data	O
processed	O
in	O
the	O
field	O
by	O
the	O
network	O
itself	O
(	O
by	O
transferring	O
small	O
amounts	O
of	O
data	O
between	O
neighboring	O
sensors	O
)	O
is	O
faster	O
and	O
makes	O
the	O
network	O
more	O
scalable	B-Architecture
.	O
</s>
<s>
One	O
barrier	O
to	O
the	O
implementation	O
of	O
WATS	O
is	O
the	O
size	O
,	O
weight	O
,	O
energy	O
requirements	O
and	O
cost	O
of	O
currently	O
available	O
wireless	B-Architecture
sensors	I-Architecture
.	O
</s>
<s>
Using	O
low-power	O
electronics	O
,	O
WSN:s	O
can	O
be	O
cost-efficiently	O
applied	O
also	O
in	O
supply	O
chains	O
in	O
various	O
industries	O
.	O
</s>
<s>
Because	O
of	O
the	O
interference	O
between	O
the	O
different	O
users	O
,	O
access	O
conflicts	O
,	O
fading	O
,	O
and	O
the	O
change	O
of	O
environment	O
in	O
the	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
,	O
traditional	O
layered	O
approach	O
for	O
wired	O
networks	O
is	O
not	O
applicable	O
to	O
wireless	O
networks	O
.	O
</s>
<s>
Sensor	B-Device
nodes	I-Device
can	O
be	O
imagined	O
as	O
small	O
computers	O
which	O
are	O
extremely	O
basic	O
in	O
terms	O
of	O
their	O
interfaces	O
and	O
their	O
components	O
.	O
</s>
<s>
They	O
usually	O
consist	O
of	O
a	O
processing	O
unit	O
with	O
limited	O
computational	O
power	O
and	O
limited	O
memory	O
,	O
sensors	O
or	O
MEMS	B-Architecture
(	O
including	O
specific	O
conditioning	O
circuitry	O
)	O
,	O
a	O
communication	O
device	O
(	O
usually	O
radio	O
transceivers	O
or	O
alternatively	O
optical	B-Device
)	O
,	O
and	O
a	O
power	O
source	O
usually	O
in	O
the	O
form	O
of	O
a	O
battery	O
.	O
</s>
<s>
RS-232	O
or	O
USB	B-Protocol
)	O
.	O
</s>
<s>
The	O
base	O
stations	O
are	O
one	O
or	O
more	O
components	O
of	O
the	O
WSN	B-Architecture
with	O
much	O
more	O
computational	O
,	O
energy	O
and	O
communication	O
resources	O
.	O
</s>
<s>
They	O
act	O
as	O
a	O
gateway	O
between	O
sensor	B-Device
nodes	I-Device
and	O
the	O
end	O
user	O
as	O
they	O
typically	O
forward	O
data	O
from	O
the	O
WSN	B-Architecture
on	O
to	O
a	O
server	B-Application
.	O
</s>
<s>
Other	O
special	O
components	O
in	O
routing	B-Protocol
based	O
networks	O
are	O
routers	O
,	O
designed	O
to	O
compute	O
,	O
calculate	O
and	O
distribute	O
the	O
routing	B-Protocol
tables	O
.	O
</s>
<s>
One	O
major	O
challenge	O
in	O
a	O
WSN	B-Architecture
is	O
to	O
produce	O
low	O
cost	O
and	O
tiny	O
sensor	B-Device
nodes	I-Device
.	O
</s>
<s>
There	O
are	O
an	O
increasing	O
number	O
of	O
small	O
companies	O
producing	O
WSN	B-Architecture
hardware	O
and	O
the	O
commercial	O
situation	O
can	O
be	O
compared	O
to	O
home	O
computing	O
in	O
the	O
1970s	O
.	O
</s>
<s>
Also	O
inherent	O
to	O
sensor	B-Architecture
network	I-Architecture
adoption	O
is	O
the	O
use	O
of	O
very	O
low	O
power	O
methods	O
for	O
radio	O
communication	O
and	O
data	O
acquisition	O
.	O
</s>
<s>
In	O
many	O
applications	O
,	O
a	O
WSN	B-Architecture
communicates	O
with	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
or	O
wide	O
area	O
network	O
through	O
a	O
gateway	O
.	O
</s>
<s>
The	O
Gateway	O
acts	O
as	O
a	O
bridge	O
between	O
the	O
WSN	B-Architecture
and	O
the	O
other	O
network	O
.	O
</s>
<s>
This	O
enables	O
data	O
to	O
be	O
stored	O
and	O
processed	O
by	O
devices	O
with	O
more	O
resources	O
,	O
for	O
example	O
,	O
in	O
a	O
remotely	O
located	O
server	B-Application
.	O
</s>
<s>
A	O
wireless	O
wide	O
area	O
network	O
used	O
primarily	O
for	O
low-power	O
devices	O
is	O
known	O
as	O
a	O
Low-Power	B-General_Concept
Wide-Area	I-General_Concept
Network	I-General_Concept
(	O
LPWAN	B-General_Concept
)	O
.	O
</s>
<s>
There	O
are	O
several	O
wireless	O
standards	O
and	O
solutions	O
for	O
sensor	B-Device
node	I-Device
connectivity	O
.	O
</s>
<s>
Thread	B-Operating_System
and	O
Zigbee	B-Protocol
can	O
connect	O
sensors	O
operating	O
at	O
2.4GHz	O
with	O
a	O
data	O
rate	O
of	O
250kbit/s	O
.	O
</s>
<s>
Many	O
use	O
a	O
lower	O
frequency	O
to	O
increase	O
radio	O
range	O
(	O
typically	O
1km	O
)	O
,	O
for	O
example	O
Z-wave	B-Device
operates	O
at	O
915MHz	O
and	O
in	O
the	O
EU	O
868MHz	O
has	O
been	O
widely	O
used	O
but	O
these	O
have	O
a	O
lower	O
data	O
rate	O
(	O
typically	O
50	O
kbit/s	O
)	O
.	O
</s>
<s>
With	O
the	O
emergence	O
of	O
Internet	B-Operating_System
of	I-Operating_System
Things	I-Operating_System
,	O
many	O
other	O
proposals	O
have	O
been	O
made	O
to	O
provide	O
sensor	O
connectivity	O
.	O
</s>
<s>
LoRa	O
is	O
a	O
form	O
of	O
LPWAN	B-General_Concept
which	O
provides	O
long	O
range	O
low	O
power	O
wireless	O
connectivity	O
for	O
devices	O
,	O
which	O
has	O
been	O
used	O
in	O
smart	O
meters	O
and	O
other	O
long	O
range	O
sensor	O
applications	O
.	O
</s>
<s>
NarrowBand	O
IOT	B-Operating_System
and	O
LTE-M	O
can	O
connect	O
up	O
to	O
millions	O
of	O
sensors	O
and	O
devices	O
using	O
cellular	O
technology	O
.	O
</s>
<s>
Energy	O
is	O
the	O
scarcest	O
resource	O
of	O
WSN	B-Architecture
nodes	O
,	O
and	O
it	O
determines	O
the	O
lifetime	O
of	O
WSNs	B-Architecture
.	O
</s>
<s>
WSNs	B-Architecture
may	O
be	O
deployed	O
in	O
large	O
numbers	O
in	O
various	O
environments	O
,	O
including	O
remote	O
and	O
hostile	O
regions	O
,	O
where	O
ad	O
hoc	O
communications	O
are	O
a	O
key	O
component	O
.	O
</s>
<s>
Lifetime	O
maximization	O
:	O
Energy/Power	O
Consumption	O
of	O
the	O
sensing	O
device	O
should	O
be	O
minimized	O
and	O
sensor	B-Device
nodes	I-Device
should	O
be	O
energy	O
efficient	O
since	O
their	O
limited	O
energy	O
resource	O
determines	O
their	O
lifetime	O
.	O
</s>
<s>
To	O
conserve	O
power	O
,	O
wireless	B-Architecture
sensor	I-Architecture
nodes	O
normally	O
power	O
off	O
both	O
the	O
radio	O
transmitter	O
and	O
the	O
radio	O
receiver	O
when	O
not	O
in	O
use	O
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
are	O
composed	O
of	O
low-energy	O
,	O
small-size	O
,	O
and	O
low-range	O
unattended	O
sensor	B-Device
nodes	I-Device
.	O
</s>
<s>
Recently	O
,	O
it	O
has	O
been	O
observed	O
that	O
by	O
periodically	O
turning	O
on	O
and	O
off	O
the	O
sensing	O
and	O
communication	O
capabilities	O
of	O
sensor	B-Device
nodes	I-Device
,	O
we	O
can	O
significantly	O
reduce	O
the	O
active	O
time	O
and	O
thus	O
prolong	O
network	O
lifetime	O
.	O
</s>
<s>
However	O
,	O
this	O
duty	O
cycling	O
may	O
result	O
in	O
high	O
network	O
latency	O
,	O
routing	B-Protocol
overhead	O
,	O
and	O
neighbor	O
discovery	O
delays	O
due	O
to	O
asynchronous	O
sleep	O
and	O
wake-up	O
scheduling	O
.	O
</s>
<s>
These	O
limitations	O
call	O
for	O
a	O
countermeasure	O
for	O
duty-cycled	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
which	O
should	O
minimize	O
routing	B-Protocol
information	I-Protocol
,	O
routing	B-Protocol
traffic	O
load	O
,	O
and	O
energy	O
consumption	O
.	O
</s>
<s>
Researchers	O
from	O
Sungkyunkwan	O
University	O
have	O
proposed	O
a	O
lightweight	O
non-increasing	O
delivery-latency	O
interval	O
routing	B-Protocol
referred	O
as	O
LNDIR	O
.	O
</s>
<s>
Simulation	O
experiments	O
demonstrated	O
the	O
validity	O
of	O
this	O
novel	O
approach	O
in	O
minimizing	O
routing	B-Protocol
information	I-Protocol
stored	O
at	O
each	O
sensor	O
.	O
</s>
<s>
Furthermore	O
,	O
this	O
novel	O
routing	B-Protocol
can	O
also	O
guarantee	O
the	O
minimum	O
delivery	O
latency	O
from	O
each	O
source	O
to	O
the	O
sink	O
.	O
</s>
<s>
Performance	O
improvements	O
of	O
up	O
to	O
12-fold	O
and	O
11-fold	O
are	O
observed	O
in	O
terms	O
of	O
routing	B-Protocol
traffic	O
load	O
reduction	O
and	O
energy	O
efficiency	O
,	O
respectively	O
,	O
as	O
compared	O
to	O
existing	O
schemes	O
.	O
</s>
<s>
Operating	B-General_Concept
systems	I-General_Concept
for	O
wireless	B-Architecture
sensor	I-Architecture
network	I-Architecture
nodes	O
are	O
typically	O
less	O
complex	O
than	O
general-purpose	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
They	O
more	O
strongly	O
resemble	O
embedded	B-Architecture
systems	I-Architecture
,	O
for	O
two	O
reasons	O
.	O
</s>
<s>
First	O
,	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
are	O
typically	O
deployed	O
with	O
a	O
particular	O
application	O
in	O
mind	O
,	O
rather	O
than	O
as	O
a	O
general	O
platform	O
.	O
</s>
<s>
Second	O
,	O
a	O
need	O
for	O
low	O
costs	O
and	O
low	O
power	O
leads	O
most	O
wireless	B-Architecture
sensor	I-Architecture
nodes	O
to	O
have	O
low-power	O
microcontrollers	B-Architecture
ensuring	O
that	O
mechanisms	O
such	O
as	O
virtual	O
memory	O
are	O
either	O
unnecessary	O
or	O
too	O
expensive	O
to	O
implement	O
.	O
</s>
<s>
It	O
is	O
therefore	O
possible	O
to	O
use	O
embedded	B-Architecture
operating	B-General_Concept
systems	I-General_Concept
such	O
as	O
eCos	B-Operating_System
or	O
uC/OS	B-Operating_System
for	O
sensor	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
However	O
,	O
such	O
operating	B-General_Concept
systems	I-General_Concept
are	O
often	O
designed	O
with	O
real-time	O
properties	O
.	O
</s>
<s>
TinyOS	B-Device
,	O
developed	O
by	O
David	O
Culler	O
,	O
is	O
perhaps	O
the	O
first	O
operating	B-General_Concept
system	I-General_Concept
specifically	O
designed	O
for	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
.	O
</s>
<s>
TinyOS	B-Device
is	O
based	O
on	O
an	O
event-driven	B-Application
programming	I-Application
model	O
instead	O
of	O
multithreading	B-Operating_System
.	O
</s>
<s>
TinyOS	B-Device
programs	O
are	O
composed	O
of	O
event	O
handlers	O
and	O
tasks	O
with	O
run-to-completion	O
semantics	O
.	O
</s>
<s>
When	O
an	O
external	O
event	O
occurs	O
,	O
such	O
as	O
an	O
incoming	O
data	O
packet	O
or	O
a	O
sensor	O
reading	O
,	O
TinyOS	B-Device
signals	O
the	O
appropriate	O
event	O
handler	O
to	O
handle	O
the	O
event	O
.	O
</s>
<s>
Event	O
handlers	O
can	O
post	O
tasks	O
that	O
are	O
scheduled	O
by	O
the	O
TinyOS	B-Device
kernel	O
some	O
time	O
later	O
.	O
</s>
<s>
LiteOS	B-Operating_System
is	O
a	O
newly	O
developed	O
OS	O
for	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
,	O
which	O
provides	O
UNIX-like	O
abstraction	O
and	O
support	O
for	O
the	O
C	O
programming	O
language	O
.	O
</s>
<s>
Contiki	B-Operating_System
,	O
developed	O
by	O
Adam	O
Dunkels	O
,	O
is	O
an	O
OS	O
which	O
uses	O
a	O
simpler	O
programming	O
style	O
in	O
C	O
while	O
providing	O
advances	O
such	O
as	O
6LoWPAN	B-Protocol
and	O
Protothreads	B-Operating_System
.	O
</s>
<s>
RIOT	B-Device
(	O
operating	B-General_Concept
system	I-General_Concept
)	O
is	O
a	O
more	O
recent	O
real-time	O
OS	O
including	O
similar	O
functionality	O
to	O
Contiki	B-Operating_System
.	O
</s>
<s>
PreonVM	O
is	O
an	O
OS	O
for	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
,	O
which	O
provides	O
6LoWPAN	B-Protocol
based	O
on	O
Contiki	B-Operating_System
and	O
support	O
for	O
the	O
Java	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
At	O
present	O
,	O
agent-based	O
modeling	O
and	O
simulation	O
is	O
the	O
only	O
paradigm	O
which	O
allows	O
the	O
simulation	O
of	O
complex	O
behavior	O
in	O
the	O
environments	O
of	O
wireless	B-Architecture
sensors	I-Architecture
(	O
such	O
as	O
flocking	O
)	O
.	O
</s>
<s>
Agent-based	O
simulation	O
of	O
wireless	B-Architecture
sensor	I-Architecture
and	O
ad	O
hoc	O
networks	O
is	O
a	O
relatively	O
new	O
paradigm	O
.	O
</s>
<s>
Network	O
simulators	O
like	O
Opnet	O
,	O
Tetcos	O
NetSim	O
and	O
NS	O
can	O
be	O
used	O
to	O
simulate	O
a	O
wireless	B-Architecture
sensor	I-Architecture
network	I-Architecture
.	O
</s>
<s>
Network	O
localization	O
refers	O
to	O
the	O
problem	O
of	O
estimating	O
the	O
location	O
of	O
wireless	B-Architecture
sensor	I-Architecture
nodes	O
during	O
deployments	O
and	O
in	O
dynamic	O
settings	O
.	O
</s>
<s>
In	O
2000	O
,	O
Nirupama	O
Bulusu	O
,	O
John	O
Heidemann	O
and	O
Deborah	O
Estrin	O
first	O
motivated	O
and	O
proposed	O
a	O
radio	O
connectivity	O
based	O
system	O
for	O
localization	O
of	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
.	O
</s>
<s>
Subsequently	O
,	O
such	O
localization	O
systems	O
have	O
been	O
referred	O
to	O
as	O
range	O
free	O
localization	O
systems	O
,	O
and	O
many	O
localization	O
systems	O
for	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
have	O
been	O
subsequently	O
proposed	O
including	O
AHLoS	O
,	O
APS	O
,	O
and	O
Stardust	O
.	O
</s>
<s>
Sensors	O
and	O
devices	O
used	O
in	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
are	O
state-of-the-art	O
technology	O
with	O
the	O
lowest	O
possible	O
price	O
.	O
</s>
<s>
Researchers	O
studying	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
hypothesize	O
that	O
much	O
more	O
information	O
can	O
be	O
extracted	O
from	O
hundreds	O
of	O
unreliable	O
measurements	O
spread	O
across	O
a	O
field	O
of	O
interest	O
than	O
from	O
a	O
smaller	O
number	O
of	O
high-quality	O
,	O
high-reliability	O
instruments	O
with	O
the	O
same	O
total	O
cost	O
.	O
</s>
<s>
It	O
refers	O
to	O
programming	O
the	O
entire	O
sensor	B-Architecture
network	I-Architecture
as	O
an	O
ensemble	O
,	O
rather	O
than	O
individual	O
sensor	B-Device
nodes	I-Device
.	O
</s>
<s>
Another	O
way	O
to	O
macro-program	O
a	O
network	O
is	O
to	O
view	O
the	O
sensor	B-Architecture
network	I-Architecture
as	O
a	O
database	O
,	O
which	O
was	O
popularized	O
by	O
the	O
TinyDB	O
system	O
developed	O
by	O
Sam	O
Madden	O
.	O
</s>
<s>
Reprogramming	O
is	O
the	O
process	O
of	O
updating	O
the	O
code	O
on	O
the	O
sensor	B-Device
nodes	I-Device
.	O
</s>
<s>
of	O
WSNs	B-Architecture
might	O
pose	O
several	O
weak	O
points	O
that	O
attract	O
adversaries	O
.	O
</s>
<s>
Therefore	O
,	O
security	O
is	O
a	O
big	O
concern	O
when	O
WSNs	B-Architecture
are	O
deployed	O
for	O
special	O
applications	O
such	O
as	O
military	O
and	O
healthcare	O
.	O
</s>
<s>
Owing	O
to	O
their	O
unique	O
characteristics	O
,	O
traditional	O
security	O
methods	O
of	O
computer	B-Architecture
networks	I-Architecture
would	O
be	O
useless	O
(	O
or	O
less	O
effective	O
)	O
for	O
WSNs	B-Architecture
.	O
</s>
<s>
There	O
have	O
been	O
important	O
innovations	O
in	O
securing	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
.	O
</s>
<s>
Most	O
wireless	O
embedded	B-Architecture
networks	O
use	O
omni-directional	O
antennas	O
and	O
therefore	O
neighbors	O
can	O
overhear	O
communication	O
in	O
and	O
out	O
of	O
nodes	O
.	O
</s>
<s>
If	O
a	O
centralized	O
architecture	O
is	O
used	O
in	O
a	O
sensor	B-Architecture
network	I-Architecture
and	O
the	O
central	O
node	O
fails	O
,	O
then	O
the	O
entire	O
network	O
will	O
collapse	O
,	O
however	O
the	O
reliability	O
of	O
the	O
sensor	B-Architecture
network	I-Architecture
can	O
be	O
increased	O
by	O
using	O
a	O
distributed	O
control	O
architecture	O
.	O
</s>
<s>
Distributed	O
control	O
is	O
used	O
in	O
WSNs	B-Architecture
for	O
the	O
following	O
reasons	O
:	O
</s>
<s>
Sensor	B-Device
nodes	I-Device
are	O
prone	O
to	O
failure	O
,	O
</s>
<s>
As	O
for	O
the	O
distributed	O
filtering	O
over	O
distributed	B-Architecture
sensor	I-Architecture
network	I-Architecture
.	O
</s>
<s>
The	O
data	O
gathered	O
from	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
is	O
usually	O
saved	O
in	O
the	O
form	O
of	O
numerical	O
data	O
in	O
a	O
central	O
base	O
station	O
.	O
</s>
<s>
Additionally	O
,	O
the	O
Open	O
Geospatial	O
Consortium	O
(	O
OGC	O
)	O
is	O
specifying	O
standards	O
for	O
interoperability	O
interfaces	O
and	O
metadata	O
encodings	O
that	O
enable	O
real	O
time	O
integration	O
of	O
heterogeneous	O
sensor	O
webs	O
into	O
the	O
Internet	O
,	O
allowing	O
any	O
individual	O
to	O
monitor	O
or	O
control	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
through	O
a	O
web	O
browser	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
sensing	O
and	O
monitoring	O
applications	O
,	O
it	O
is	O
generally	O
the	O
case	O
that	O
neighboring	O
sensor	B-Device
nodes	I-Device
monitoring	O
an	O
environmental	O
feature	O
typically	O
register	O
similar	O
values	O
.	O
</s>
<s>
Aggregation	O
reduces	O
the	O
amount	O
of	O
network	O
traffic	O
which	O
helps	O
to	O
reduce	O
energy	O
consumption	O
on	O
sensor	B-Device
nodes	I-Device
.	O
</s>
<s>
Recently	O
,	O
it	O
has	O
been	O
found	O
that	O
network	O
gateways	O
also	O
play	O
an	O
important	O
role	O
in	O
improving	O
energy	O
efficiency	O
of	O
sensor	B-Device
nodes	I-Device
by	O
scheduling	O
more	O
resources	O
for	O
the	O
nodes	O
with	O
more	O
critical	O
energy	O
efficiency	O
need	O
and	O
advanced	O
energy	O
efficient	O
scheduling	O
algorithms	O
need	O
to	O
be	O
implemented	O
at	O
network	O
gateways	O
for	O
the	O
improvement	O
of	O
the	O
overall	O
network	O
energy	O
efficiency	O
.	O
</s>
<s>
This	O
is	O
a	O
form	O
of	O
in-network	O
processing	O
where	O
sensor	B-Device
nodes	I-Device
are	O
assumed	O
to	O
be	O
unsecured	O
with	O
limited	O
available	O
energy	O
,	O
while	O
the	O
base	O
station	O
is	O
assumed	O
to	O
be	O
secure	O
with	O
unlimited	O
available	O
energy	O
.	O
</s>
<s>
Aggregation	O
complicates	O
the	O
already	O
existing	O
security	O
challenges	O
for	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
and	O
requires	O
new	O
security	O
techniques	O
tailored	O
specifically	O
for	O
these	O
scenarios	O
.	O
</s>
<s>
Providing	O
security	O
to	O
aggregate	O
data	O
in	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
is	O
known	O
as	O
secure	O
data	O
aggregation	O
in	O
WSN	B-Architecture
.	O
</s>
<s>
were	O
the	O
first	O
few	O
works	O
discussing	O
techniques	O
for	O
secure	O
data	O
aggregation	O
in	O
wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
.	O
</s>
<s>
While	O
encryption	O
is	O
traditionally	O
used	O
to	O
provide	O
end	O
to	O
end	O
confidentiality	O
in	O
wireless	B-Architecture
sensor	I-Architecture
network	I-Architecture
,	O
the	O
aggregators	O
in	O
a	O
secure	O
data	O
aggregation	O
scenario	O
need	O
to	O
decrypt	O
the	O
encrypted	O
data	O
to	O
perform	O
aggregation	O
.	O
</s>
