<s>
This	O
article	O
is	O
about	O
event	B-Device
detection	I-Device
for	I-Device
WSN	I-Device
.	O
</s>
<s>
Wireless	B-Architecture
sensor	I-Architecture
networks	I-Architecture
(	O
WSN	B-Architecture
)	O
are	O
a	O
spatially	O
distributed	O
network	O
of	O
autonomous	O
sensors	O
used	O
for	O
monitoring	O
an	O
environment	O
.	O
</s>
<s>
Energy	O
cost	O
is	O
a	O
major	O
limitation	O
for	O
WSN	B-Architecture
requiring	O
the	O
need	O
for	O
energy	O
efficient	O
networks	O
and	O
processing	O
.	O
</s>
<s>
One	O
of	O
major	O
energy	O
costs	O
in	O
WSN	B-Architecture
is	O
the	O
energy	O
spent	O
on	O
communication	O
between	O
nodes	O
and	O
it	O
is	O
sometimes	O
desirable	O
to	O
only	O
send	O
data	O
to	O
a	O
gateway	B-Data_Structure
node	I-Data_Structure
when	O
an	O
event	O
of	O
interest	O
is	O
triggered	O
at	O
a	O
sensor	O
.	O
</s>
<s>
Data	O
collected	O
at	O
a	O
sensor	O
node	O
,	O
also	O
called	O
the	O
data-event	B-General_Concept
,	O
is	O
analyzed	O
to	O
see	O
if	O
it	O
has	O
reached	O
a	O
certain	O
threshold	O
point	O
to	O
be	O
considered	O
an	O
event	O
.	O
</s>
<s>
The	O
data-event	B-General_Concept
can	O
also	O
be	O
the	O
result	O
of	O
a	O
combination	O
of	O
outputs	O
from	O
different	O
types	O
of	O
sensors	O
that	O
either	O
collaborate	O
at	O
the	O
gateway	O
or	O
through	O
small	O
hop	O
peer-to-peer	O
communication	O
.	O
</s>
<s>
If	O
sensors	O
collect	O
multiple	O
data	O
points	O
at	O
a	O
given	O
time	O
then	O
another	O
method	O
of	O
using	O
threshold	O
based	O
detection	O
is	O
to	O
measure	O
the	O
variance	O
of	O
the	O
data	O
and	O
only	O
send	O
data	O
to	O
a	O
gateway	B-Data_Structure
node	I-Data_Structure
if	O
the	O
variance	O
reaches	O
a	O
certain	O
threshold	O
.	O
</s>
<s>
The	O
sum	B-Algorithm
of	I-Algorithm
absolute	I-Algorithm
difference	I-Algorithm
can	O
be	O
calculated	O
for	O
all	O
the	O
samples	O
in	O
that	O
section	O
and	O
can	O
be	O
used	O
as	O
an	O
approximation	O
of	O
the	O
variance	O
of	O
that	O
quadrant	O
.	O
</s>
<s>
The	O
sum	B-Algorithm
of	I-Algorithm
absolute	I-Algorithm
difference	I-Algorithm
above	O
is	O
one	O
quadrant	O
of	O
the	O
total	O
space	O
sampled	O
and	O
can	O
represent	O
the	O
pseudo-variance	O
of	O
a	O
subset	O
of	O
the	O
data	O
.	O
</s>
<s>
If	O
the	O
probability	O
of	O
an	O
event	O
is	O
large	O
enough	O
then	O
the	O
data	O
is	O
forwarded	O
to	O
the	O
gateway	B-Data_Structure
node	I-Data_Structure
.	O
</s>
<s>
Below	O
are	O
a	O
few	O
examples	O
of	O
algorithms	O
that	O
solve	O
the	O
optimal	O
Bayes	B-General_Concept
classifier	I-General_Concept
.	O
</s>
<s>
The	O
k-NN	B-General_Concept
algorithm	I-General_Concept
is	O
a	O
well	O
known	O
pattern	O
recognition	O
algorithm	O
where	O
a	O
set	O
of	O
predetermined	O
prototypes	B-Application
 { pk } 	O
are	O
used	O
during	O
the	O
sample	O
,	O
or	O
testing	O
phase	O
,	O
of	O
a	O
supposed	O
event	O
.	O
</s>
<s>
The	O
prototypes	B-Application
model	O
the	O
events	O
that	O
are	O
of	O
interest	O
in	O
the	O
application	O
.	O
</s>
<s>
The	O
distance	O
between	O
each	O
test	O
vector	O
and	O
each	O
prototype	B-Application
is	O
calculated	O
and	O
the	O
k	O
test	O
vectors	O
closest	O
to	O
the	O
prototype	B-Application
vectors	O
are	O
taken	O
as	O
the	O
most	O
likely	O
classification	O
or	O
group	O
of	O
classifications	O
.	O
</s>
<s>
From	O
there	O
the	O
probability	O
that	O
x	O
belongs	O
to	O
the	O
prototype	B-Application
event	O
can	O
be	O
calculated	O
.	O
</s>
<s>
This	O
approach	O
,	O
however	O
,	O
requires	O
much	O
memory	O
and	O
processing	O
power	O
as	O
the	O
number	O
of	O
prototypes	B-Application
increases	O
and	O
thus	O
it	O
is	O
not	O
a	O
very	O
practical	O
choice	O
for	O
WSNs	B-Architecture
.	O
</s>
<s>
A	O
support	B-Algorithm
vector	I-Algorithm
machine	I-Algorithm
maps	O
a	O
set	O
of	O
linear	O
transformations	O
from	O
the	O
N-dimensional	O
input	O
vector	O
to	O
a	O
higher	O
M-dimensional	O
feature	O
space	O
.	O
</s>
<s>
A	O
linear	B-General_Concept
classifier	I-General_Concept
can	O
be	O
described	O
as	O
a	O
determinant	O
function	O
that	O
satisfies	O
,	O
if	O
for	O
.	O
</s>
<s>
The	O
linear	B-General_Concept
classifier	I-General_Concept
for	O
this	O
support	B-Algorithm
vector	I-Algorithm
machine	I-Algorithm
classifier	O
is	O
,	O
</s>
<s>
This	O
is	O
an	O
active	O
area	O
of	O
research	O
for	O
event	O
detection	O
and	O
other	O
applications	O
in	O
WSNs	B-Architecture
.	O
</s>
