<s>
A	O
single-frequency	B-Device
network	I-Device
or	O
SFN	O
is	O
a	O
broadcast	B-Operating_System
network	O
where	O
several	O
transmitters	O
simultaneously	O
send	O
the	O
same	O
signal	O
over	O
the	O
same	O
frequency	O
channel	O
.	O
</s>
<s>
Analog	O
AM	B-Device
and	O
FM	B-Application
radio	O
broadcast	B-Operating_System
networks	O
as	O
well	O
as	O
digital	O
broadcast	B-Operating_System
networks	O
can	O
operate	O
in	O
this	O
manner	O
.	O
</s>
<s>
A	O
simplified	O
form	O
of	O
SFN	O
can	O
be	O
achieved	O
by	O
a	O
low	O
power	O
co-channel	O
repeater	O
,	O
booster	O
or	O
broadcast	B-Operating_System
translator	O
,	O
which	O
is	O
utilized	O
as	O
a	O
gap	O
filler	O
transmitter	O
.	O
</s>
<s>
The	O
aim	O
of	O
SFNs	O
is	O
efficient	O
utilization	O
of	O
the	O
radio	B-Algorithm
spectrum	I-Algorithm
,	O
allowing	O
a	O
higher	O
number	O
of	O
radio	O
and	O
TV	O
programs	O
in	O
comparison	O
to	O
traditional	O
multi-frequency	B-Protocol
network	I-Protocol
(	O
MFN	O
)	O
transmission	O
.	O
</s>
<s>
SFN	O
schemes	O
are	O
somewhat	O
analogous	O
to	O
what	O
in	O
non-broadcast	O
wireless	O
communication	O
,	O
for	O
example	O
cellular	O
networks	O
and	O
wireless	O
computer	O
networks	O
,	O
is	O
called	O
transmitter	O
macrodiversity	B-Protocol
,	O
CDMA	B-Protocol
soft	B-Protocol
handoff	I-Protocol
and	O
Dynamic	B-Protocol
Single	I-Protocol
Frequency	I-Protocol
Networks	I-Protocol
(	O
DSFN	B-Protocol
)	O
.	O
</s>
<s>
Fading	O
and	O
ISI	O
can	O
be	O
avoided	O
by	O
means	O
of	O
diversity	B-Protocol
schemes	I-Protocol
and	O
equalization	B-Algorithm
filters	O
.	O
</s>
<s>
In	O
wideband	O
digital	O
broadcasting	B-Operating_System
,	O
self-interference	B-Protocol
cancellation	I-Protocol
is	O
facilitated	O
by	O
the	O
OFDM	B-Protocol
or	O
COFDM	B-Protocol
modulation	B-Application
method	O
.	O
</s>
<s>
OFDM	B-Protocol
uses	O
a	O
large	O
number	O
of	O
slow	O
low-bandwidth	O
modulators	B-Application
instead	O
of	O
one	O
fast	O
wide-band	O
modulator	B-Application
.	O
</s>
<s>
Each	O
modulator	B-Application
has	O
its	O
own	O
frequency	O
sub-channel	O
and	O
sub-carrier	O
frequency	O
.	O
</s>
<s>
Since	O
each	O
modulator	B-Application
is	O
very	O
slow	O
,	O
we	O
can	O
afford	O
to	O
insert	O
a	O
guard	B-Protocol
interval	I-Protocol
between	O
the	O
symbols	O
,	O
and	O
thus	O
eliminate	O
the	O
ISI	O
.	O
</s>
<s>
Thus	O
,	O
advanced	O
equalization	B-Algorithm
filters	O
can	O
be	O
avoided	O
.	O
</s>
<s>
A	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
code	O
(	O
FEC	O
)	O
can	O
counteract	O
some	O
of	O
the	O
sub-carriers	O
being	O
exposed	O
to	O
too	O
much	O
fading	O
to	O
be	O
correctly	O
demodulated	O
.	O
</s>
<s>
OFDM	B-Protocol
is	O
utilized	O
in	O
the	O
terrestrial	O
digital	B-Application
TV	I-Application
broadcasting	B-Operating_System
system	O
DVB-T	O
(	O
used	O
in	O
Europe	O
and	O
other	O
regions	O
)	O
,	O
ISDB-T	O
(	O
used	O
in	O
Japan	O
and	O
Brazil	O
)	O
and	O
in	O
ATSC	B-Device
3.0	I-Device
.	O
</s>
<s>
OFDM	B-Protocol
is	O
also	O
widely	O
used	O
in	O
digital	O
radio	O
systems	O
,	O
including	O
DAB	O
,	O
HD	O
Radio	O
,	O
and	O
T-DMB	O
.	O
</s>
<s>
In	O
DVB-T	O
a	O
SFN	O
functionality	O
is	O
described	O
as	O
a	O
system	O
in	O
the	O
implementation	O
guide	O
.	O
</s>
<s>
The	O
DVB-T	O
SFN	O
uses	O
the	O
fact	O
that	O
the	O
guard	B-Protocol
interval	I-Protocol
of	O
the	O
COFDM	B-Protocol
signal	O
allows	O
for	O
various	O
length	O
of	O
path	O
echoes	O
to	O
occur	O
is	O
not	O
different	O
from	O
that	O
of	O
multiple	O
transmitters	O
transmitting	O
the	O
same	O
signal	O
onto	O
the	O
same	O
frequency	O
.	O
</s>
<s>
The	O
guard	B-Protocol
interval	I-Protocol
allows	O
for	O
a	O
timing	O
budget	O
,	O
of	O
which	O
several	O
microseconds	O
may	O
be	O
allocated	O
to	O
time	O
errors	O
of	O
the	O
time-transfer	O
system	O
used	O
.	O
</s>
<s>
A	O
GPS	O
receiver	O
worst-case	O
scenario	O
is	O
able	O
to	O
provide	O
+	O
/	O
-	O
1	O
µs	O
time	O
,	O
well	O
within	O
the	O
system	O
needs	O
of	O
DVB-T	O
SFN	O
in	O
typical	O
configuration	O
.	O
</s>
<s>
While	O
not	O
designed	O
with	O
on-channel	B-Device
repeaters	I-Device
in	O
mind	O
,	O
the	O
8VSB	B-Device
modulation	B-Application
method	O
used	O
in	O
North	O
America	O
for	O
digital	B-Application
TV	I-Application
is	O
relatively	O
good	O
at	O
ghost	O
cancellation	O
.	O
</s>
<s>
Early	O
experiments	O
at	O
WPSU-TV	O
led	O
to	O
an	O
ATSC	B-Device
standard	I-Device
for	O
SFNs	O
,	O
A/110	O
.	O
</s>
<s>
ATSC	B-Device
SFNs	O
have	O
seen	O
widest	O
use	O
in	O
mountainous	O
areas	O
like	O
Puerto	O
Rico	O
and	O
Southern	O
California	O
,	O
but	O
are	O
also	O
in	O
use	O
or	O
planned	O
in	O
gentler	O
terrain	O
.	O
</s>
<s>
Early	O
ATSC	B-Device
tuners	I-Device
were	O
not	O
very	O
good	O
at	O
handling	O
multipath	O
propagation	O
,	O
but	O
later	O
systems	O
have	O
seen	O
significant	O
improvements	O
.	O
</s>
<s>
Through	O
the	O
use	O
of	O
virtual	B-Protocol
channel	I-Protocol
numbering	O
,	O
a	O
multi-frequency	B-Protocol
network	I-Protocol
(	O
MFN	O
)	O
can	O
appear	O
as	O
an	O
SFN	O
to	O
the	O
viewer	O
in	O
ATSC	B-Device
.	O
</s>
<s>
Alternatives	O
to	O
using	O
OFDM	B-Protocol
modulation	B-Application
in	O
SFN	O
self-interference	B-Protocol
cancellation	I-Protocol
would	O
be	O
:	O
</s>
<s>
CDMA	B-Protocol
Rake	O
receivers	O
.	O
</s>
<s>
Single-carrier	O
frequency-domain-equalization	O
(	O
SC-FDE	O
)	O
,	O
i.e.	O
</s>
<s>
single-carrier	O
modulation	B-Application
combined	O
with	O
guard	B-Protocol
intervals	I-Protocol
and	O
FFT-based	O
frequency	O
domain	O
equalization	B-Algorithm
,	O
or	O
its	O
multi-user	O
version	O
Single-carrier	O
FDMA	O
(	O
SC-FDMA	O
)	O
.	O
</s>
