<s>
Cooperative	B-Protocol
diversity	I-Protocol
is	O
a	O
cooperative	O
multiple	O
antenna	O
technique	O
for	O
improving	O
or	O
maximising	O
total	O
network	O
channel	O
capacities	O
for	O
any	O
given	O
set	O
of	O
bandwidths	O
which	O
exploits	O
user	O
diversity	B-Protocol
by	O
decoding	O
the	O
combined	O
signal	O
of	O
the	O
relayed	O
signal	O
and	O
the	O
direct	O
signal	O
in	O
wireless	O
multihop	B-General_Concept
networks	O
.	O
</s>
<s>
A	O
conventional	O
single	O
hop	O
system	O
uses	O
direct	O
transmission	O
where	O
a	O
receiver	O
decodes	O
the	O
information	O
only	O
based	O
on	O
the	O
direct	O
signal	O
while	O
regarding	O
the	O
relayed	O
signal	O
as	O
interference	O
,	O
whereas	O
the	O
cooperative	B-Protocol
diversity	I-Protocol
considers	O
the	O
other	O
signal	O
as	O
contribution	O
.	O
</s>
<s>
That	O
is	O
,	O
cooperative	B-Protocol
diversity	I-Protocol
decodes	O
the	O
information	O
from	O
the	O
combination	O
of	O
two	O
signals	O
.	O
</s>
<s>
Hence	O
,	O
it	O
can	O
be	O
seen	O
that	O
cooperative	B-Protocol
diversity	I-Protocol
is	O
an	O
antenna	O
diversity	B-Protocol
that	O
uses	O
distributed	O
antennas	O
belonging	O
to	O
each	O
node	O
in	O
a	O
wireless	O
network	O
.	O
</s>
<s>
Note	O
that	O
user	O
cooperation	O
is	O
another	O
definition	O
of	O
cooperative	B-Protocol
diversity	I-Protocol
.	O
</s>
<s>
User	O
cooperation	O
considers	O
an	O
additional	O
fact	O
that	O
each	O
user	O
relays	O
the	O
other	O
user	O
's	O
signal	O
while	O
cooperative	B-Protocol
diversity	I-Protocol
can	O
be	O
also	O
achieved	O
by	O
multi-hop	O
relay	O
networking	O
systems	O
.	O
</s>
<s>
The	O
cooperative	B-Protocol
diversity	I-Protocol
technique	O
is	O
a	O
kind	O
of	O
multi-user	B-Architecture
MIMO	I-Architecture
technique	O
.	O
</s>
<s>
Since	O
the	O
two	O
communications	O
took	O
a	O
different	O
path	O
and	O
take	O
place	O
one	O
after	O
another	O
,	O
this	O
example	O
implements	O
the	O
concept	O
of	O
space	O
diversity	B-Protocol
and	O
time	O
diversity	B-Protocol
.	O
</s>
<s>
Relays	O
following	O
the	O
decode-and-forward	O
strategy	O
overhear	O
transmissions	O
from	O
the	O
source	O
,	O
decode	O
them	O
and	O
in	O
case	O
of	O
correct	B-Error_Name
decoding	I-Error_Name
,	O
forward	O
them	O
to	O
the	O
destination	O
.	O
</s>
<s>
It	O
provides	O
power	O
gain	O
and	O
diversity	B-Protocol
gain	I-Protocol
simultaneously	O
.	O
</s>
<s>
There	O
is	O
no	O
increase	O
in	O
the	O
diversity	B-Protocol
order	O
since	O
this	O
scheme	O
exploits	O
only	O
the	O
relayed	O
signal	O
and	O
the	O
direct	O
signal	O
from	O
the	O
source	O
node	O
is	O
either	O
not	O
available	O
or	O
is	O
not	O
accounted	O
for	O
.	O
</s>
<s>
When	O
we	O
can	O
take	O
advantage	O
of	O
such	O
a	O
signal	O
and	O
increase	O
in	O
diversity	B-Protocol
order	O
results	O
.	O
</s>
<s>
For	O
cooperative	O
decoding	O
,	O
the	O
destination	O
node	O
combines	O
two	O
signals	O
received	O
from	O
the	O
source	O
and	O
the	O
relay	O
nodes	O
which	O
results	O
in	O
the	O
diversity	B-Protocol
advantage	O
.	O
</s>
<s>
It	O
is	O
noteworthy	O
that	O
cooperative	B-Protocol
diversity	I-Protocol
can	O
increase	O
the	O
diversity	B-Protocol
gain	I-Protocol
at	O
the	O
cost	O
of	O
losing	O
the	O
wireless	O
resource	O
such	O
as	O
frequency	O
,	O
time	O
and	O
power	O
resources	O
for	O
the	O
relaying	O
phase	O
.	O
</s>
<s>
Hence	O
,	O
it	O
is	O
important	O
to	O
remark	O
that	O
there	O
is	O
trade-off	O
between	O
the	O
diversity	B-Protocol
gain	I-Protocol
and	O
the	O
waste	O
of	O
the	O
spectrum	O
resource	O
in	O
cooperative	B-Protocol
diversity	I-Protocol
.	O
</s>
<s>
Note	O
that	O
the	O
max-flow	B-Algorithm
min-cut	I-Algorithm
theorem	I-Algorithm
states	O
that	O
the	O
maximum	O
amount	O
of	O
flow	O
is	O
equal	O
to	O
the	O
capacity	O
of	O
a	O
minimum	O
cut	O
,	O
i.e.	O
,	O
dictated	O
by	O
its	O
bottleneck	O
.	O
</s>
<s>
In	O
a	O
cognitive	B-Protocol
radio	I-Protocol
system	O
,	O
unlicensed	O
secondary	O
users	O
can	O
use	O
the	O
resources	O
which	O
is	O
licensed	O
for	O
primary	O
users	O
.	O
</s>
<s>
A	O
wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
network	I-General_Concept
is	O
an	O
autonomous	O
and	O
self	O
organizing	O
network	O
without	O
any	O
centralized	O
controller	O
or	O
pre-established	O
infrastructure	O
.	O
</s>
<s>
A	O
wireless	B-Architecture
sensor	I-Architecture
network	I-Architecture
can	O
use	O
cooperative	O
relaying	O
to	O
reduce	O
the	O
energy	O
consumption	O
in	O
sensor	O
nodes	O
,	O
hence	O
lifetime	O
of	O
sensor	B-Architecture
network	I-Architecture
increases	O
.	O
</s>
