<s>
Multi-user	B-Architecture
MIMO	I-Architecture
(	O
MU-MIMO	B-Architecture
)	O
is	O
a	O
set	O
of	O
multiple-input	O
and	O
multiple-output	O
(	O
MIMO	O
)	O
technologies	O
for	O
multipath	O
wireless	O
communication	O
,	O
in	O
which	O
multiple	O
users	O
or	O
terminals	O
,	O
each	O
radioing	O
over	O
one	O
or	O
more	O
antennas	O
,	O
communicate	O
with	O
one	O
another	O
.	O
</s>
<s>
Analogous	O
to	O
how	O
OFDMA	O
adds	O
multiple-access	O
capability	O
to	O
OFDM	B-Protocol
in	O
the	O
cellular-communications	O
realm	O
,	O
MU-MIMO	B-Architecture
adds	O
multiple-user	O
capability	O
to	O
MIMO	O
in	O
the	O
wireless	O
realm	O
.	O
</s>
<s>
SDMA	O
,	O
massive	O
MIMO	O
,	O
coordinated	O
multipoint	O
(	O
CoMP	O
)	O
,	O
and	O
ad	O
hoc	O
MIMO	O
are	O
all	O
related	O
to	O
MU-MIMO	B-Architecture
;	O
each	O
of	O
those	O
technologies	O
often	O
leverage	O
spatial	O
degrees	O
of	O
freedom	O
to	O
separate	O
users	O
.	O
</s>
<s>
MU-MIMO	B-Architecture
leverages	O
multiple	O
users	O
as	O
spatially	O
distributed	O
transmission	O
resources	O
,	O
at	O
the	O
cost	O
of	O
somewhat	O
more	O
expensive	O
signal	O
processing	O
.	O
</s>
<s>
MU-MIMO	B-Architecture
algorithms	O
enhance	O
MIMO	O
systems	O
where	O
connections	O
among	O
users	O
count	O
greater	O
than	O
one	O
.	O
</s>
<s>
MU-MIMO	B-Architecture
may	O
be	O
generalized	O
into	O
two	O
categories	O
:	O
MIMO	O
broadcast	O
channels	O
(	O
MIMO	O
BC	O
)	O
and	O
MIMO	O
multiple-access	O
channels	O
(	O
MIMO	O
MAC	O
)	O
for	O
downlink	O
and	O
uplink	O
situations	O
,	O
respectively	O
.	O
</s>
<s>
Examples	O
of	O
advanced-transmit	O
processing	O
for	O
MIMO	O
BC	O
are	O
interference-aware	O
precoding	B-Protocol
and	O
SDMA-based	O
downlink	O
user	O
scheduling	O
.	O
</s>
<s>
The	O
categories	O
of	O
precoding	B-Protocol
techniques	O
which	O
may	O
be	O
used	O
by	O
MIMO	O
BC	O
include	O
,	O
one	O
,	O
those	O
using	O
dirty	O
paper	O
coding	O
(	O
DPC	O
)	O
and	O
linear	O
techniques	O
and	O
two	O
,	O
hybrid	O
(	O
analog	O
and	O
digital	O
)	O
techniques	O
.	O
</s>
<s>
The	O
highly	O
interconnected	O
wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
network	I-General_Concept
increases	O
the	O
flexibility	O
of	O
wireless	O
networking	O
at	O
the	O
cost	O
of	O
increased	O
multi-user	O
interference	O
.	O
</s>
<s>
Cooperative	B-Protocol
diversity	I-Protocol
–	O
Achieve	O
antenna	O
diversity	O
gain	O
by	O
the	O
cooperation	O
of	O
distributed	O
antennas	O
belonging	O
to	O
each	O
independent	O
node	O
.	O
</s>
<s>
Cooperative	O
relay	O
–	O
Apply	O
cooperative	O
concepts	O
onto	O
relay	O
techniques	O
,	O
which	O
is	O
similar	O
to	O
cooperative	B-Protocol
diversity	I-Protocol
in	O
terms	O
of	O
cooperative	O
signalling	O
.	O
</s>
<s>
However	O
,	O
the	O
main	O
criterion	O
of	O
cooperative	O
relay	O
is	O
to	O
improve	O
the	O
tradeoff	O
region	O
between	O
delay	O
and	O
performance	O
,	O
while	O
that	O
of	O
cooperative	B-Protocol
diversity	I-Protocol
and	O
MIMO	O
is	O
to	O
improve	O
the	O
link	O
and	O
system	O
performance	O
at	O
the	O
expense	O
of	O
minimal	O
cooperation	O
loss	O
.	O
</s>
<s>
CO-MIMO	B-Architecture
,	O
also	O
known	O
as	O
network	B-Architecture
MIMO	I-Architecture
(	O
net-MIMO	O
)	O
,	O
or	O
ad	O
hoc	O
MIMO	O
,	O
uses	O
distributed	O
antennas	O
which	O
belong	O
to	O
other	O
users	O
,	O
while	O
conventional	O
MIMO	O
,	O
i.e.	O
,	O
single-user	O
MIMO	O
,	O
only	O
employs	O
antennas	O
belonging	O
to	O
the	O
local	O
terminal	O
.	O
</s>
<s>
CO-MIMO	B-Architecture
improves	O
the	O
performance	O
of	O
a	O
wireless	O
network	O
by	O
introducing	O
multiple	O
antenna	O
advantages	O
,	O
such	O
as	O
diversity	O
,	O
multiplexing	O
and	O
beamforming	B-Algorithm
.	O
</s>
<s>
If	O
the	O
main	O
interest	O
hinges	O
on	O
the	O
diversity	O
gain	O
,	O
it	O
is	O
known	O
as	O
cooperative	B-Protocol
diversity	I-Protocol
.	O
</s>
<s>
It	O
can	O
be	O
described	O
as	O
a	O
form	O
of	O
macro-diversity	B-Protocol
,	O
used	O
for	O
example	O
in	O
soft	B-Protocol
handover	I-Protocol
.	O
</s>
<s>
Cooperative	O
MIMO	O
corresponds	O
to	O
transmitter	O
macro-diversity	B-Protocol
or	O
simulcasting	O
.	O
</s>
<s>
A	O
simple	O
form	O
that	O
does	O
not	O
require	O
any	O
advanced	O
signal	O
processing	O
is	O
single	B-Device
frequency	I-Device
networks	I-Device
(	O
SFN	O
)	O
,	O
used	O
especially	O
in	O
wireless	O
broadcasting	O
.	O
</s>
<s>
SFNs	O
combined	O
with	O
channel	O
adaptive	O
or	O
traffic	O
adaptive	O
scheduling	O
is	O
called	O
dynamic	B-Protocol
single	I-Protocol
frequency	I-Protocol
networks	I-Protocol
(	O
DSFN	B-Protocol
)	O
.	O
</s>
<s>
CO-MIMO	B-Architecture
is	O
a	O
technique	O
useful	O
for	O
future	O
cellular	O
networks	O
which	O
consider	O
wireless	O
mesh	B-Architecture
networking	I-Architecture
or	O
wireless	O
ad	O
hoc	O
networking	O
.	O
</s>
<s>
In	O
wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
networks	I-General_Concept
,	O
multiple	O
transmit	O
nodes	O
communicate	O
with	O
multiple	O
receive	O
nodes	O
.	O
</s>
<s>
Strategies	O
such	O
as	O
autonomous	B-Protocol
interference	I-Protocol
cognition	I-Protocol
,	O
node	O
cooperation	O
,	O
and	O
network	O
coding	O
with	O
dirty	O
paper	O
coding	O
have	O
been	O
suggested	O
to	O
optimize	O
wireless	O
network	O
capacity	O
.	O
</s>
