<s>
In	O
radio	B-Protocol
resource	I-Protocol
management	I-Protocol
for	O
wireless	O
and	O
cellular	O
networks	O
,	O
channel	B-Protocol
allocation	I-Protocol
schemes	I-Protocol
allocate	O
bandwidth	B-Algorithm
and	O
communication	O
channels	O
to	O
base	O
stations	O
,	O
access	O
points	O
and	O
terminal	O
equipment	O
.	O
</s>
<s>
The	O
objective	O
is	O
to	O
achieve	O
maximum	O
system	O
spectral	B-Protocol
efficiency	I-Protocol
in	O
bit/s/Hz/site	O
by	O
means	O
of	O
frequency	O
reuse	O
,	O
but	O
still	O
assure	O
a	O
certain	O
grade	O
of	O
service	O
by	O
avoiding	O
co-channel	O
interference	O
and	O
adjacent	O
channel	O
interference	O
among	O
nearby	O
cells	O
or	O
networks	O
that	O
share	O
the	O
bandwidth	B-Algorithm
.	O
</s>
<s>
In	O
Fixed	B-Protocol
Channel	I-Protocol
Allocation	I-Protocol
or	O
Fixed	O
Channel	O
Assignment	O
(	O
FCA	O
)	O
each	O
cell	O
is	O
given	O
a	O
predetermined	O
set	O
of	O
frequency	O
channels	O
.	O
</s>
<s>
There	O
are	O
however	O
several	O
dynamic	O
radio-resource	B-Protocol
management	I-Protocol
schemes	O
that	O
can	O
be	O
combined	O
with	O
FCA	O
.	O
</s>
<s>
If	O
FCA	O
is	O
combined	O
with	O
spread	B-Architecture
spectrum	I-Architecture
,	O
the	O
maximum	O
number	O
of	O
channels	O
is	O
not	O
fixed	O
in	O
theory	O
,	O
but	O
in	O
practice	O
a	O
maximum	O
limit	O
is	O
applied	O
,	O
since	O
too	O
many	O
calls	O
would	O
cause	O
too	O
high	O
co-channel	O
interference	O
level	O
,	O
causing	O
the	O
quality	O
to	O
be	O
problematic	O
.	O
</s>
<s>
Spread	B-Architecture
spectrum	I-Architecture
allows	O
cell	O
breathing	O
to	O
be	O
applied	O
,	O
by	O
allowing	O
an	O
overloaded	O
cell	O
to	O
borrow	O
capacity	O
(	O
maximum	O
number	O
of	O
simultaneous	O
calls	O
in	O
the	O
cell	O
)	O
from	O
a	O
nearby	O
cell	O
that	O
is	O
sharing	O
the	O
same	O
frequency	O
.	O
</s>
<s>
Dynamic	O
Frequency	O
Selection	O
(	O
DFS	O
)	O
is	O
a	O
mechanism	O
specified	O
for	O
wireless	O
networks	O
with	O
non-centrally	O
controlled	O
access	O
points	O
,	O
such	O
as	O
wireless	B-Architecture
LAN	I-Architecture
(	O
commonly	O
Wi-Fi	O
)	O
.	O
</s>
<s>
It	O
is	O
designed	O
to	O
prevent	O
interference	O
with	O
other	O
usages	O
of	O
the	O
frequency	O
band	O
,	O
such	O
as	O
military	B-Application
radar	I-Application
,	O
satellite	O
communication	O
,	O
and	O
weather	B-Application
radar	I-Application
.	O
</s>
<s>
In	O
case	O
of	O
wireless	B-Architecture
LAN	I-Architecture
standard	O
,	O
DFS	O
was	O
standardized	O
in	O
2003	O
as	O
part	O
of	O
IEEE	B-Protocol
802.11h	I-Protocol
.	O
</s>
<s>
It	O
is	O
often	O
enforced	O
for	O
the	O
frequency	O
bands	O
used	O
by	O
Terminal	B-Algorithm
Doppler	I-Algorithm
Weather	I-Algorithm
Radar	I-Algorithm
and	O
C-Band	B-Algorithm
satellite	I-Algorithm
communication	O
.	O
</s>
<s>
The	O
misconfiguration	O
of	O
DFS	O
had	O
caused	O
significant	O
disruption	O
in	O
weather	B-Application
radar	I-Application
operation	O
during	O
early	O
deployments	O
of	O
5GHz	O
Wi-Fi	O
in	O
a	O
number	O
of	O
countries	O
in	O
the	O
world	O
.	O
</s>
<s>
For	O
example	O
,	O
DFS	O
is	O
also	O
mandated	O
in	O
the	O
5470-5725MHz	O
U-NII	B-Algorithm
band	I-Algorithm
for	O
radar	B-Application
avoidance	O
in	O
United	O
States	O
.	O
</s>
<s>
A	O
more	O
efficient	O
way	O
of	O
channel	B-Protocol
allocation	I-Protocol
would	O
be	O
Dynamic	O
Channel	B-Protocol
Allocation	I-Protocol
or	O
Dynamic	B-Protocol
Channel	I-Protocol
Assignment	I-Protocol
(	O
DCA	O
)	O
in	O
which	O
voice	O
channel	O
are	O
not	O
allocated	O
to	O
cell	O
permanently	O
,	O
instead	O
for	O
every	O
call	O
request	O
base	O
station	O
request	O
channel	O
from	O
MSC	O
.	O
</s>
<s>
OFDMA	O
systems	O
,	O
such	O
as	O
the	O
downlink	O
of	O
4G	B-Architecture
cellular	O
systems	O
,	O
can	O
be	O
considered	O
as	O
carrying	O
out	O
DCA	O
for	O
each	O
individual	O
sub-carrier	O
as	O
well	O
as	O
each	O
timeslot	O
.	O
</s>
<s>
Spread	B-Architecture
spectrum	I-Architecture
can	O
be	O
considered	O
as	O
an	O
alternative	O
to	O
complex	O
DCA	O
algorithms	O
.	O
</s>
<s>
Spread	B-Architecture
spectrum	I-Architecture
avoids	O
cochannel	O
interference	O
between	O
adjacent	O
cells	O
,	O
since	O
the	O
probability	O
that	O
users	O
in	O
nearby	O
cells	O
use	O
the	O
same	O
spreading	O
code	O
is	O
insignificant	O
.	O
</s>
<s>
Thus	O
the	O
frequency	O
channel	B-Protocol
allocation	I-Protocol
problem	O
is	O
relaxed	O
in	O
cellular	O
networks	O
based	O
on	O
a	O
combination	O
of	O
spread	B-Architecture
spectrum	I-Architecture
and	O
FDMA	O
,	O
for	O
example	O
IS95	O
and	O
3G	B-Architecture
systems	O
.	O
</s>
<s>
Spread	B-Architecture
spectrum	I-Architecture
also	O
facilitate	O
that	O
centrally	O
controlled	O
base	O
stations	O
dynamically	O
borrow	O
resources	O
from	O
each	O
other	O
depending	O
on	O
the	O
traffic	O
load	O
,	O
simply	O
by	O
increasing	O
the	O
maximum	O
allowed	O
number	O
of	O
simultaneous	O
users	O
in	O
one	O
cell	O
(	O
the	O
maximum	O
allowed	O
interference	O
level	O
from	O
the	O
users	O
in	O
the	O
cell	O
)	O
,	O
and	O
decreasing	O
it	O
in	O
an	O
adjacent	O
cell	O
.	O
</s>
<s>
However	O
,	O
spread	B-Architecture
spectrum	I-Architecture
gives	O
lower	O
spectral	B-Protocol
efficiency	I-Protocol
than	O
non-spread	O
spectrum	O
techniques	O
,	O
if	O
the	O
channel	B-Protocol
allocation	I-Protocol
in	O
the	O
latter	O
case	O
is	O
optimized	O
by	O
a	O
good	O
DCA	O
scheme	O
.	O
</s>
<s>
Especially	O
OFDM	B-Protocol
modulation	O
is	O
an	O
interesting	O
alternative	O
to	O
spread	B-Architecture
spectrum	I-Architecture
because	O
of	O
its	O
ability	O
to	O
combat	O
multipath	O
propagation	O
for	O
wideband	O
channels	O
without	O
complex	O
equalization	O
.	O
</s>
<s>
OFDM	B-Protocol
can	O
be	O
extended	O
with	O
OFDMA	O
for	O
uplink	O
multiple	O
access	O
among	O
users	O
in	O
the	O
same	O
cell	O
.	O
</s>
<s>
One	O
example	O
of	O
this	O
concept	O
is	O
the	O
above	O
mentioned	O
IEEE	B-Protocol
802.11h	I-Protocol
standard	O
.	O
</s>
<s>
OFDM	B-Protocol
and	O
OFDMA	O
with	O
DCA	O
is	O
often	O
studied	O
as	O
an	O
alternative	O
for	O
4G	B-Architecture
wireless	I-Architecture
systems	O
.	O
</s>
<s>
For	O
high	O
system	B-Protocol
spectrum	I-Protocol
efficiency	I-Protocol
,	O
DCA	O
should	O
be	O
performed	O
on	O
a	O
packet-by-packet	O
basis	O
.	O
</s>
<s>
Examples	O
of	O
algorithms	O
for	O
packet-by-packet	O
DCA	O
are	O
Dynamic	O
Packet	O
Assignment	O
(	O
DPA	O
)	O
,	O
Dynamic	B-Protocol
Single	I-Protocol
Frequency	I-Protocol
Networks	I-Protocol
(	O
DSFN	B-Protocol
)	O
and	O
Packet	O
and	O
resource	O
plan	O
scheduling	O
(	O
PARPS	O
)	O
.	O
</s>
