<s>
A	O
cognitive	B-Protocol
radio	I-Protocol
(	O
CR	O
)	O
is	O
a	O
radio	O
that	O
can	O
be	O
programmed	O
and	O
configured	O
dynamically	O
to	O
use	O
the	O
best	O
wireless	O
channels	O
in	O
its	O
vicinity	O
to	O
avoid	O
user	O
interference	O
and	O
congestion	O
.	O
</s>
<s>
Such	O
a	O
radio	O
automatically	O
detects	O
available	O
channels	O
in	O
wireless	B-Algorithm
spectrum	I-Algorithm
,	O
then	O
accordingly	O
changes	O
its	O
transmission	O
or	O
reception	O
parameters	O
to	O
allow	O
more	O
concurrent	O
wireless	O
communications	O
in	O
a	O
given	O
spectrum	O
band	O
at	O
one	O
location	O
.	O
</s>
<s>
This	O
functions	O
as	O
an	O
autonomous	O
unit	O
in	O
the	O
communications	O
environment	O
,	O
exchanging	O
information	O
about	O
the	O
environment	O
with	O
the	O
networks	O
it	O
accesses	O
and	O
other	O
cognitive	B-Protocol
radios	I-Protocol
(	O
CRs	O
)	O
.	O
</s>
<s>
Some	O
"	O
smart	O
radio	O
"	O
proposals	O
combine	O
wireless	O
mesh	O
network	O
—	O
dynamically	O
changing	O
the	O
path	O
messages	O
take	O
between	O
two	O
given	O
nodes	O
using	O
cooperative	B-Protocol
diversity	I-Protocol
;	O
cognitive	B-Protocol
radio	I-Protocol
—	O
dynamically	O
changing	O
the	O
frequency	O
band	O
used	O
by	O
messages	O
between	O
two	O
consecutive	O
nodes	O
on	O
the	O
path	O
;	O
and	O
software-defined	B-Architecture
radio	I-Architecture
—	O
dynamically	O
changing	O
the	O
protocol	O
used	O
by	O
message	O
between	O
two	O
consecutive	O
nodes	O
.	O
</s>
<s>
The	O
concept	O
of	O
cognitive	B-Protocol
radio	I-Protocol
was	O
first	O
proposed	O
by	O
Joseph	O
Mitola	O
III	O
in	O
a	O
seminar	O
at	O
KTH	O
Royal	O
Institute	O
of	O
Technology	O
in	O
Stockholm	O
in	O
1998	O
and	O
published	O
in	O
an	O
article	O
by	O
Mitola	O
and	O
Gerald	O
Q	O
.	O
Maguire	O
,	O
Jr.	O
in	O
1999	O
.	O
</s>
<s>
The	O
point	O
in	O
which	O
wireless	O
personal	B-Application
digital	I-Application
assistants	I-Application
(	O
PDAs	B-Application
)	O
and	O
the	O
related	O
networks	O
are	O
sufficiently	O
computationally	O
intelligent	O
about	O
radio	O
resources	O
and	O
related	O
computer-to-computer	O
communications	O
to	O
detect	O
user	O
communications	O
needs	O
as	O
a	O
function	O
of	O
use	O
context	O
,	O
and	O
to	O
provide	O
radio	O
resources	O
and	O
wireless	O
services	O
most	O
appropriate	O
to	O
those	O
needs	O
.	O
</s>
<s>
Cognitive	B-Protocol
radio	I-Protocol
is	O
considered	O
as	O
a	O
goal	O
towards	O
which	O
a	O
software-defined	B-Architecture
radio	I-Architecture
platform	O
should	O
evolve	O
:	O
a	O
fully	O
reconfigurable	O
wireless	O
transceiver	O
which	O
automatically	O
adapts	O
its	O
communication	O
parameters	O
to	O
network	O
and	O
user	O
demands	O
.	O
</s>
<s>
Traditional	O
regulatory	O
structures	O
have	O
been	O
built	O
for	O
an	O
analog	O
model	O
and	O
are	O
not	O
optimized	O
for	O
cognitive	B-Protocol
radio	I-Protocol
.	O
</s>
<s>
The	O
first	O
cognitive	B-Protocol
radio	I-Protocol
wireless	O
regional	O
area	O
network	O
standard	O
,	O
IEEE	O
802.22	O
,	O
was	O
developed	O
by	O
IEEE	O
802	O
LAN/MAN	O
Standard	O
Committee	O
(	O
LMSC	O
)	O
and	O
published	O
in	O
2011	O
.	O
</s>
<s>
Geolocation	O
combines	O
with	O
a	O
database	O
of	O
licensed	O
transmitters	O
in	O
the	O
area	O
to	O
identify	O
available	O
channels	O
for	O
use	O
by	O
the	O
cognitive	B-Protocol
radio	I-Protocol
network	O
.	O
</s>
<s>
However	O
,	O
cognitive	B-Protocol
radio	I-Protocol
cannot	O
occupy	O
the	O
same	O
unused	O
space	O
all	O
the	O
time	O
.	O
</s>
<s>
Depending	O
on	O
transmission	O
and	O
reception	O
parameters	O
,	O
there	O
are	O
two	O
main	O
types	O
of	O
cognitive	B-Protocol
radio	I-Protocol
:	O
</s>
<s>
Full	O
Cognitive	B-Protocol
Radio	I-Protocol
(	O
Mitola	O
radio	O
)	O
,	O
in	O
which	O
every	O
possible	O
parameter	O
observable	O
by	O
a	O
wireless	O
node	O
(	O
or	O
network	O
)	O
is	O
considered	O
.	O
</s>
<s>
Spectrum-Sensing	O
Cognitive	B-Protocol
Radio	I-Protocol
,	O
in	O
which	O
only	O
the	O
radio-frequency	O
spectrum	O
is	O
considered	O
.	O
</s>
<s>
Other	O
types	O
are	O
dependent	O
on	O
parts	O
of	O
the	O
spectrum	O
available	O
for	O
cognitive	B-Protocol
radio	I-Protocol
:	O
</s>
<s>
Licensed-Band	O
Cognitive	B-Protocol
Radio	I-Protocol
,	O
capable	O
of	O
using	O
bands	O
assigned	O
to	O
licensed	O
users	O
(	O
except	O
for	O
unlicensed	B-Algorithm
bands	I-Algorithm
,	O
such	O
as	O
the	O
U-NII	B-Algorithm
band	I-Algorithm
or	O
the	O
ISM	B-Algorithm
band	I-Algorithm
)	O
.	O
</s>
<s>
The	O
IEEE	O
802.22	O
working	O
group	O
is	O
developing	O
a	O
standard	O
for	O
wireless	O
regional	O
area	O
network	O
(	O
WRAN	O
)	O
,	O
which	O
will	O
operate	O
on	O
unused	O
television	O
channels	O
,	O
also	O
known	O
as	O
TV	B-Operating_System
white	O
spaces	O
.	O
</s>
<s>
Unlicensed-Band	O
Cognitive	B-Protocol
Radio	I-Protocol
,	O
which	O
can	O
only	O
utilize	O
unlicensed	O
parts	O
of	O
the	O
radio	O
frequency	O
(	O
RF	O
)	O
spectrum	O
.	O
</s>
<s>
One	O
such	O
system	O
is	O
described	O
in	O
the	O
IEEE	O
802.15	O
Task	O
Group	O
2	O
specifications	O
,	O
which	O
focus	O
on	O
the	O
coexistence	O
of	O
IEEE	O
802.11	O
and	O
Bluetooth	B-Protocol
.	O
</s>
<s>
Haykin	O
,	O
"	O
Cognitive	B-Protocol
Radio	I-Protocol
:	O
Brain-empowered	O
Wireless	O
Communications	O
"	O
,	O
IEEE	O
Journal	O
on	O
Selected	O
Areas	O
of	O
Communications	O
,	O
vol	O
.	O
</s>
<s>
201	O
–	O
220	O
,	O
Feb	O
.	O
2005	O
:	O
Spectrum	O
sharing	O
cognitive	B-Architecture
radio	I-Architecture
networks	I-Architecture
allow	O
cognitive	B-Protocol
radio	I-Protocol
users	O
to	O
share	O
the	O
spectrum	O
bands	O
of	O
the	O
licensed-band	O
users	O
.	O
</s>
<s>
However	O
,	O
the	O
cognitive	B-Protocol
radio	I-Protocol
users	O
have	O
to	O
restrict	O
their	O
transmit	O
power	O
so	O
that	O
the	O
interference	O
caused	O
to	O
the	O
licensed-band	O
users	O
is	O
kept	O
below	O
a	O
certain	O
threshold	O
.	O
</s>
<s>
Sensing-based	O
Spectrum	O
sharing	O
:	O
In	O
sensing-based	O
spectrum	O
sharing	O
cognitive	B-Architecture
radio	I-Architecture
networks	I-Architecture
,	O
cognitive	B-Protocol
radio	I-Protocol
users	O
first	O
listen	O
to	O
the	O
spectrum	O
allocated	O
to	O
the	O
licensed	O
users	O
to	O
detect	O
the	O
state	O
of	O
the	O
licensed	O
users	O
.	O
</s>
<s>
Based	O
on	O
the	O
detection	O
results	O
,	O
cognitive	B-Protocol
radio	I-Protocol
users	O
decide	O
their	O
transmission	O
strategies	O
.	O
</s>
<s>
If	O
the	O
licensed	O
users	O
are	O
not	O
using	O
the	O
bands	O
,	O
cognitive	B-Protocol
radio	I-Protocol
users	O
will	O
transmit	O
over	O
those	O
bands	O
.	O
</s>
<s>
If	O
the	O
licensed	O
users	O
are	O
using	O
the	O
bands	O
,	O
cognitive	B-Protocol
radio	I-Protocol
users	O
share	O
the	O
spectrum	O
bands	O
with	O
the	O
licensed	O
users	O
by	O
restricting	O
their	O
transmit	O
power	O
.	O
</s>
<s>
Database-enabled	O
Spectrum	O
Sharing	O
,,	O
:	O
In	O
this	O
modality	O
of	O
spectrum	O
sharing	O
,	O
cognitive	B-Protocol
radio	I-Protocol
users	O
are	O
required	O
to	O
access	O
a	O
white	O
space	O
database	O
prior	O
to	O
be	O
allowed	O
,	O
or	O
denied	O
,	O
access	O
to	O
the	O
shared	O
spectrum	O
.	O
</s>
<s>
The	O
white	O
space	O
database	O
contain	O
algorithms	O
,	O
mathematical	O
models	O
and	O
local	O
regulations	O
to	O
predict	O
the	O
spectrum	O
utilization	O
in	O
a	O
geographical	O
area	O
and	O
to	O
infer	O
on	O
the	O
risk	O
of	O
interference	O
posed	O
to	O
incumbent	O
services	O
by	O
a	O
cognitive	B-Protocol
radio	I-Protocol
user	O
accessing	O
the	O
shared	O
spectrum	O
.	O
</s>
<s>
If	O
the	O
white	O
space	O
database	O
judges	O
that	O
destructive	O
interference	O
to	O
incumbents	O
will	O
happen	O
,	O
the	O
cognitive	B-Protocol
radio	I-Protocol
user	O
is	O
denied	O
access	O
to	O
the	O
shared	O
spectrum	O
.	O
</s>
<s>
Although	O
cognitive	B-Protocol
radio	I-Protocol
was	O
initially	O
thought	O
of	O
as	O
a	O
software-defined	B-Architecture
radio	I-Architecture
extension	O
(	O
full	O
cognitive	B-Protocol
radio	I-Protocol
)	O
,	O
most	O
research	O
work	O
focuses	O
on	O
spectrum-sensing	O
cognitive	B-Protocol
radio	I-Protocol
(	O
particularly	O
in	O
the	O
TV	B-Operating_System
bands	O
)	O
.	O
</s>
<s>
The	O
chief	O
problem	O
in	O
spectrum-sensing	O
cognitive	B-Protocol
radio	I-Protocol
is	O
designing	O
high-quality	O
spectrum-sensing	O
devices	O
and	O
algorithms	O
for	O
exchanging	O
spectrum-sensing	O
data	O
between	O
nodes	O
.	O
</s>
<s>
Timo	O
A	O
.	O
Weiss	O
and	O
Friedrich	O
K	O
.	O
Jondral	O
of	O
the	O
University	O
of	O
Karlsruhe	O
proposed	O
a	O
spectrum	B-Algorithm
pooling	I-Algorithm
system	O
,	O
in	O
which	O
free	O
bands	O
(	O
sensed	O
by	O
nodes	O
)	O
were	O
immediately	O
filled	O
by	O
OFDMA	O
subbands	O
.	O
</s>
<s>
Applications	O
of	O
spectrum-sensing	O
cognitive	B-Protocol
radio	I-Protocol
include	O
emergency-network	O
and	O
WLAN	B-Architecture
higher	O
throughput	O
and	O
transmission-distance	O
extensions	O
.	O
</s>
<s>
The	O
evolution	O
of	O
cognitive	B-Protocol
radio	I-Protocol
toward	O
cognitive	B-Architecture
networks	I-Architecture
is	O
underway	O
;	O
the	O
concept	O
of	O
cognitive	B-Architecture
networks	I-Architecture
is	O
to	O
intelligently	O
organize	O
a	O
network	O
of	O
cognitive	B-Protocol
radios	I-Protocol
.	O
</s>
<s>
The	O
main	O
functions	O
of	O
cognitive	B-Protocol
radios	I-Protocol
are	O
:	O
</s>
<s>
Transmitter	O
detection	O
:	O
Cognitive	B-Protocol
radios	I-Protocol
must	O
have	O
the	O
capability	O
to	O
determine	O
if	O
a	O
signal	O
from	O
a	O
primary	O
transmitter	O
is	O
locally	O
present	O
in	O
a	O
certain	O
spectrum	O
.	O
</s>
<s>
Cyclostationary-feature	O
detection	O
:	O
These	O
type	O
of	O
spectrum	O
sensing	O
algorithms	O
are	O
motivated	O
because	O
most	O
man-made	O
communication	O
signals	O
,	O
such	O
as	O
BPSK	B-General_Concept
,	O
QPSK	B-General_Concept
,	O
AM	B-Device
,	O
OFDM	B-Protocol
,	O
etc	O
.	O
</s>
<s>
Cognitive	B-Protocol
radios	I-Protocol
should	O
decide	O
on	O
the	O
best	O
spectrum	O
band	O
(	O
of	O
all	O
bands	O
available	O
)	O
to	O
meet	O
quality	O
of	O
service	O
requirements	O
;	O
therefore	O
,	O
spectrum-management	O
functions	O
are	O
required	O
for	O
cognitive	B-Protocol
radios	I-Protocol
.	O
</s>
<s>
An	O
example	O
of	O
the	O
former	O
is	O
choosing	O
an	O
appropriate	O
sensing	O
threshold	O
to	O
detect	O
other	O
users	O
,	O
while	O
the	O
latter	O
is	O
exemplified	O
by	O
the	O
need	O
to	O
meet	O
the	O
rules	O
and	O
regulations	O
set	O
out	O
for	O
radio	B-Algorithm
spectrum	I-Algorithm
access	O
in	O
international	O
(	O
ITU	O
radio	O
regulations	O
)	O
and	O
national	O
(	O
telecommunications	O
law	O
)	O
legislation	O
.	O
</s>
<s>
Cognitive	B-Protocol
radio	I-Protocol
,	O
by	O
comparison	O
,	O
allows	O
user	O
terminals	O
to	O
sense	O
whether	O
a	O
portion	O
of	O
the	O
spectrum	O
is	O
being	O
used	O
in	O
order	O
to	O
share	O
spectrum	O
with	O
neighbor	O
users	O
.	O
</s>
<s>
Cognitive	B-Protocol
Radio	I-Protocol
(	O
CR	O
)	O
can	O
sense	O
its	O
environment	O
and	O
,	O
without	O
the	O
intervention	O
of	O
the	O
user	O
,	O
can	O
adapt	O
to	O
the	O
user	O
's	O
communications	O
needs	O
while	O
conforming	O
to	O
FCC	O
rules	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
All	O
of	O
these	O
capabilities	O
,	O
and	O
others	O
yet	O
to	O
be	O
realized	O
,	O
will	O
provide	O
wireless	B-Algorithm
spectrum	I-Algorithm
users	O
with	O
the	O
ability	O
to	O
adapt	O
to	O
real-time	O
spectrum	O
conditions	O
,	O
offering	O
regulators	O
,	O
licenses	O
and	O
the	O
general	O
public	O
flexible	O
,	O
efficient	O
and	O
comprehensive	O
use	O
of	O
the	O
spectrum	O
"	O
.	O
</s>
<s>
Cognitive	B-Protocol
radio	I-Protocol
is	O
practical	O
also	O
to	O
wireless	O
sensor	O
networks	O
,	O
where	O
packet	O
relaying	O
can	O
take	O
place	O
using	O
primary	O
and	O
secondary	O
queues	O
to	O
forward	O
packets	O
without	O
delays	O
and	O
with	O
minimum	O
power	O
consumption	O
.	O
</s>
<s>
At	O
present	O
,	O
modeling	O
&	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
a	O
given	O
environment	O
's	O
cognitive	B-Architecture
radio	I-Architecture
networks	I-Architecture
.	O
</s>
<s>
Network	O
simulators	O
like	O
OPNET	O
,	O
NetSim	O
,	O
MATLAB	B-Language
and	O
ns2	B-Language
can	O
be	O
used	O
to	O
simulate	O
a	O
cognitive	B-Protocol
radio	I-Protocol
network	O
.	O
</s>
<s>
CogNS	O
is	O
an	O
open-source	O
NS2-based	O
simulation	O
framework	O
for	O
cognitive	B-Architecture
radio	I-Architecture
networks	I-Architecture
.	O
</s>
<s>
Network	O
Simulator	O
3	O
(	O
ns-3	B-Language
)	O
is	O
also	O
a	O
viable	O
option	O
for	O
simulating	O
CR	O
.	O
</s>
<s>
ns-3	B-Language
can	O
be	O
also	O
used	O
to	O
emulate	O
and	O
experiment	O
CR	O
networks	O
with	O
the	O
aid	O
from	O
commodity	O
hardware	O
like	O
Atheros	O
WiFi	O
devices	O
.	O
</s>
<s>
The	O
success	O
of	O
the	O
unlicensed	B-Algorithm
band	I-Algorithm
in	O
accommodating	O
a	O
range	O
of	O
wireless	O
devices	O
and	O
services	O
has	O
led	O
the	O
FCC	O
to	O
consider	O
opening	O
further	O
bands	O
for	O
unlicensed	O
use	O
.	O
</s>
<s>
Realizing	O
that	O
CR	O
technology	O
has	O
the	O
potential	O
to	O
exploit	O
the	O
inefficiently	O
utilized	O
licensed	O
bands	O
without	O
causing	O
interference	O
to	O
incumbent	O
users	O
,	O
the	O
FCC	O
released	O
a	O
Notice	O
of	O
Proposed	O
Rule	O
Making	O
which	O
would	O
allow	O
unlicensed	O
radios	O
to	O
operate	O
in	O
the	O
TV-broadcast	O
bands	O
.	O
</s>
<s>
The	O
IEEE	O
802.22	O
working	O
group	O
,	O
formed	O
in	O
November	O
2004	O
,	O
is	O
tasked	O
with	O
defining	O
the	O
air-interface	O
standard	O
for	O
wireless	O
regional	O
area	O
networks	O
(	O
based	O
on	O
CR	O
sensing	O
)	O
for	O
the	O
operation	O
of	O
unlicensed	O
devices	O
in	O
the	O
spectrum	O
allocated	O
to	O
TV	B-Operating_System
service	O
.	O
</s>
<s>
To	O
comply	O
with	O
later	O
FCC	O
regulations	O
on	O
unlicensed	O
utilization	O
of	O
TV	B-Operating_System
spectrum	O
,	O
the	O
IEEE	O
802.22	O
has	O
defined	O
interfaces	O
to	O
the	O
mandatory	O
TV	B-Operating_System
White	O
Space	O
Database	O
in	O
order	O
to	O
avoid	O
interference	O
to	O
incumbent	O
services	O
.	O
</s>
