<s>
C-RAN	B-General_Concept
(	O
Cloud-RAN	O
)	O
,	O
also	O
referred	O
to	O
as	O
Centralized-RAN	O
,	O
is	O
an	O
architecture	O
for	O
cellular	O
networks	O
.	O
</s>
<s>
C-RAN	B-General_Concept
is	O
a	O
centralized	O
,	O
cloud	O
computing-based	O
architecture	O
for	O
radio	O
access	O
networks	O
that	O
supports	O
2G	O
,	O
3G	O
,	O
4G	O
and	O
future	O
wireless	O
communication	O
standards	O
.	O
</s>
<s>
Its	O
name	O
comes	O
from	O
the	O
four	O
'	O
C	O
's	O
in	O
the	O
main	O
characteristics	O
of	O
C-RAN	B-General_Concept
system	O
,	O
"	O
Clean	O
,	O
Centralized	O
processing	O
,	O
Collaborative	O
radio	O
,	O
and	O
a	O
real-time	O
Cloud	O
Radio	O
Access	O
Network	O
"	O
.	O
</s>
<s>
Each	O
BTS	O
processes	O
and	O
transmits	O
its	O
own	O
signal	O
to	O
and	O
from	O
the	O
mobile	O
terminal	O
,	O
and	O
forwards	O
the	O
data	O
payload	O
to	O
and	O
from	O
the	O
mobile	O
terminal	O
and	O
out	O
to	O
the	O
core	B-General_Concept
network	I-General_Concept
via	O
the	O
backhaul	B-General_Concept
.	O
</s>
<s>
Usually	O
the	O
base	B-General_Concept
station	I-General_Concept
cabinet	O
was	O
placed	O
in	O
a	O
dedicated	O
room	O
along	O
with	O
all	O
necessary	O
supporting	O
facilitates	O
such	O
as	O
power	O
,	O
backup	O
battery	O
,	O
air	O
conditioning	O
,	O
environment	O
surveillance	O
,	O
and	O
backhaul	B-General_Concept
transmission	O
equipment	O
.	O
</s>
<s>
The	O
RF	O
signal	O
is	O
generated	O
by	O
the	O
base	B-General_Concept
station	I-General_Concept
RF	O
unit	O
and	O
propagates	O
through	O
pairs	O
of	O
RF	O
cables	O
up	O
to	O
the	O
antennas	O
on	O
the	O
top	O
of	O
a	O
base	B-General_Concept
station	I-General_Concept
tower	O
or	O
other	O
mounting	O
points	O
.	O
</s>
<s>
For	O
3G	O
,	O
a	O
distributed	O
base	B-General_Concept
station	I-General_Concept
architecture	O
was	O
introduced	O
by	O
Ericsson	O
,	O
Nokia	O
,	O
Huawei	O
,	O
and	O
other	O
leading	O
telecom	O
equipment	O
vendors	O
.	O
</s>
<s>
Digital	O
baseband	O
signals	O
are	O
carried	O
over	O
fiber	O
,	O
using	O
the	O
Open	O
Base	B-General_Concept
Station	I-General_Concept
Architecture	O
Initiative	O
(	O
OBSAI	O
)	O
or	O
Common	O
Public	O
Radio	O
Interface	O
(	O
CPRI	O
)	O
standard	O
.	O
</s>
<s>
The	O
RRH	O
can	O
be	O
installed	O
on	O
the	O
top	O
of	O
tower	O
close	O
to	O
the	O
antenna	O
,	O
reducing	O
the	O
loss	O
compared	O
to	O
the	O
traditional	O
base	B-General_Concept
station	I-General_Concept
where	O
the	O
RF	O
signal	O
has	O
to	O
travel	O
through	O
a	O
long	O
cable	O
from	O
the	O
base	B-General_Concept
station	I-General_Concept
cabinet	O
to	O
the	O
antenna	O
at	O
the	O
top	O
of	O
the	O
tower	O
.	O
</s>
<s>
C-RAN	B-General_Concept
may	O
be	O
viewed	O
as	O
an	O
architectural	O
evolution	O
of	O
the	O
above	O
distributed	O
base	B-General_Concept
station	I-General_Concept
system	O
.	O
</s>
<s>
For	O
example	O
,	O
it	O
uses	O
the	O
latest	O
CPRI	O
standard	O
,	O
low	O
cost	O
Coarse	O
or	O
Dense	O
Wavelength	O
Division	O
Multiplexing	O
(	O
CWDM/	O
DWDM	O
)	O
technology	O
,	O
and	O
mmWave	O
to	O
allow	O
transmission	O
of	O
baseband	O
signal	O
over	O
long	O
distance	O
thus	O
achieving	O
large	O
scale	O
centralised	O
base	B-General_Concept
station	I-General_Concept
deployment	O
.	O
</s>
<s>
C-RAN	B-General_Concept
architecture	O
has	O
the	O
following	O
characteristics	O
that	O
are	O
distinct	O
from	O
other	O
cellular	O
architectures	O
:	O
</s>
<s>
This	O
is	O
one	O
major	O
difference	O
from	O
BBU	O
Hotelling	O
,	O
or	O
base	B-General_Concept
station	I-General_Concept
Hotelling	O
;	O
in	O
the	O
latter	O
case	O
,	O
the	O
BBUs	O
of	O
different	O
base	O
stations	O
are	O
simply	O
stacked	O
together	O
and	O
have	O
no	O
direct	O
link	O
between	O
them	O
to	O
allow	O
physical	O
layer	O
co-ordination	O
.	O
</s>
<s>
In	O
contrast	O
,	O
a	O
C-RAN	B-General_Concept
BBU	O
pool	O
is	O
built	O
on	O
open	O
hardware	O
,	O
like	O
x86/ARM	O
CPU	O
based	O
servers	O
,	O
and	O
interface	O
cards	O
that	O
handle	O
fiber	O
links	O
to	O
RRHs	O
and	O
inter-connections	O
in	O
the	O
pool	O
.	O
</s>
<s>
Real-time	O
virtualization	O
ensures	O
that	O
resources	O
in	O
the	O
pool	O
can	O
be	O
allocated	O
dynamically	O
to	O
base	B-General_Concept
station	I-General_Concept
software	O
stacks	O
,	O
say	O
4G/3G/2G	O
function	O
modules	O
from	O
different	O
vendors	O
,	O
according	O
to	O
network	O
load	O
.	O
</s>
<s>
However	O
,	O
to	O
satisfy	O
the	O
strict	O
timing	O
requirements	O
of	O
wireless	O
communication	O
systems	O
,	O
the	O
real-time	O
performance	O
for	O
C-RAN	B-General_Concept
is	O
at	O
the	O
level	O
of	O
tens	O
of	O
microseconds	O
,	O
which	O
is	O
two	O
orders	O
of	O
magnitude	O
better	O
than	O
the	O
millisecond	O
level	O
'	O
real-time	O
'	O
performance	O
usually	O
seen	O
in	O
Cloud	O
Computing	O
environments	O
.	O
</s>
<s>
The	O
concept	O
of	O
CCC	O
is	O
basically	O
the	O
same	O
as	O
C-RAN	B-General_Concept
.	O
</s>
<s>
In	O
2014	O
,	O
Airvana	O
(	O
now	O
CommScope	O
)	O
introduced	O
OneCell	O
,	O
a	O
C-RAN-based	O
small	O
cell	O
system	O
designed	O
for	O
enterprises	O
and	O
public	O
spaces	O
.	O
</s>
<s>
More	O
processing	O
units	O
in	O
less-protected	O
environments	O
also	O
implies	O
a	O
higher	O
failure	O
rate	O
compared	O
to	O
C-RAN	B-General_Concept
,	O
which	O
only	O
has	O
the	O
RRU	O
deployed	O
outdoors	O
.	O
</s>
<s>
However	O
,	O
the	O
economic	O
benefit	O
of	O
improvements	O
such	O
as	O
CoMP	O
can	O
be	O
negated	O
by	O
the	O
higher	O
backhaul	B-General_Concept
costs	O
for	O
some	O
operators	O
.	O
</s>
<s>
The	O
main	O
competition	O
between	O
small	O
cell	O
and	O
C-RAN	B-General_Concept
occurs	O
in	O
two	O
deployment	O
scenarios	O
:	O
outdoor	O
hotspot	O
coverage	O
and	O
indoor	O
coverage	O
.	O
</s>
<s>
As	O
one	O
of	O
the	O
promising	O
evolution	O
paths	O
for	O
future	O
cellular	O
network	O
architecture	O
,	O
C-RAN	B-General_Concept
has	O
attracted	O
high	O
academic	O
research	O
interest	O
.	O
</s>
<s>
Meanwhile	O
,	O
because	O
the	O
native	O
support	O
of	O
cooperative	O
radio	O
capability	O
built	O
into	O
the	O
C-RAN	B-General_Concept
architecture	O
,	O
it	O
also	O
enables	O
many	O
advanced	O
algorithms	O
that	O
were	O
hard	O
to	O
implement	O
in	O
cellular	O
networks	O
,	O
including	O
Cooperative	O
Multi-Point	O
Transmission/Receiving	O
,	O
Network	O
Coding	O
,	O
etc	O
.	O
</s>
<s>
In	O
October	O
2011	O
,	O
27	O
was	O
hosted	O
in	O
Germany	O
,	O
when	O
China	O
Mobile	O
was	O
invited	O
to	O
give	O
a	O
C-RAN	B-General_Concept
presentation	O
.	O
</s>
<s>
CRC	O
Press	O
published	O
a	O
book	O
,	O
"	O
Green	O
Communications	O
:	O
Theoretical	O
Fundamentals	O
,	O
Algorithms	O
and	O
Applications	O
"	O
,	O
and	O
has	O
as	O
its	O
11th	O
chapter	O
:	O
"	O
C-RAN	B-General_Concept
:	O
A	O
Green	O
RAN	O
Framework	O
"	O
.	O
</s>
<s>
Many	O
of	O
these	O
projects	O
have	O
taken	O
C-RAN	B-General_Concept
as	O
one	O
of	O
the	O
future	O
cellular	O
network	O
architectures	O
,	O
like	O
the	O
Mobile	O
Cloud	O
Network	O
project	O
.	O
</s>
