<s>
In	O
telecommunications	O
,	O
guard	B-Protocol
intervals	I-Protocol
are	O
used	O
to	O
ensure	O
that	O
distinct	B-Protocol
transmissions	I-Protocol
do	O
not	O
interfere	O
with	O
one	O
another	O
,	O
or	O
otherwise	O
cause	O
overlapping	O
transmissions	O
.	O
</s>
<s>
These	O
transmissions	O
may	O
belong	O
to	O
different	O
users	O
(	O
as	O
in	O
TDMA	O
)	O
or	O
to	O
the	O
same	O
user	O
(	O
as	O
in	O
OFDM	B-Protocol
)	O
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
guard	B-Protocol
interval	I-Protocol
is	O
to	O
introduce	O
immunity	O
to	O
propagation	O
delays	O
,	O
echoes	O
and	O
reflections	O
,	O
to	O
which	O
digital	O
data	O
is	O
normally	O
very	O
sensitive	O
.	O
</s>
<s>
In	O
OFDM	B-Protocol
,	O
the	O
beginning	O
of	O
each	O
symbol	O
is	O
preceded	O
by	O
a	O
guard	B-Protocol
interval	I-Protocol
.	O
</s>
<s>
As	O
long	O
as	O
the	O
echoes	O
fall	O
within	O
this	O
interval	O
,	O
they	O
will	O
not	O
affect	O
the	O
receiver	O
's	O
ability	O
to	O
safely	O
decode	O
the	O
actual	O
data	O
,	O
as	O
data	O
is	O
only	O
interpreted	O
outside	O
the	O
guard	B-Protocol
interval	I-Protocol
.	O
</s>
<s>
In	O
TDMA	O
,	O
each	O
user	O
's	O
timeslot	O
ends	O
with	O
a	O
guard	B-Protocol
interval	I-Protocol
.	O
</s>
<s>
Thus	O
,	O
the	O
guard	B-Protocol
interval	I-Protocol
protects	O
against	O
data	O
loss	O
within	O
the	O
same	O
timeslot	O
,	O
and	O
protects	O
the	O
following	O
user	O
's	O
timeslot	O
from	O
interference	O
caused	O
by	O
propagation	O
delay	O
.	O
</s>
<s>
It	O
is	O
a	O
common	O
misconception	O
that	O
TDMA	O
timeslots	O
begin	O
with	O
the	O
guard	B-Protocol
interval	I-Protocol
,	O
as	O
with	O
OFDM	B-Protocol
.	O
</s>
<s>
However	O
,	O
in	O
specifications	O
for	O
TDMA	O
systems	O
such	O
as	O
GSM	O
,	O
the	O
guard	B-Protocol
period	I-Protocol
is	O
defined	O
as	O
being	O
at	O
the	O
end	O
of	O
the	O
timeslot	O
.	O
</s>
<s>
Longer	O
guard	B-Protocol
periods	I-Protocol
allow	O
more	O
distant	O
echoes	O
to	O
be	O
tolerated	O
but	O
reduce	O
channel	O
efficiency	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
DVB-T	O
,	O
guard	B-Protocol
intervals	I-Protocol
are	O
available	O
as	O
1/32	O
,	O
1/16	O
,	O
1/8	O
or	O
1/4	O
of	O
a	O
symbol	O
period	O
.	O
</s>
<s>
Ideally	O
,	O
the	O
guard	B-Protocol
interval	I-Protocol
is	O
set	O
to	O
just	O
above	O
the	O
delay	O
spread	O
of	O
the	O
channel	O
.	O
</s>
<s>
The	O
standard	O
symbol	O
guard	B-Protocol
interval	I-Protocol
used	O
in	O
IEEE	O
802.11	O
OFDM	B-Protocol
is	O
.	O
</s>
<s>
To	O
increase	O
data	O
rate	O
,	O
802.11n	O
added	O
optional	O
support	O
for	O
a	O
guard	B-Protocol
interval	I-Protocol
.	O
</s>
<s>
To	O
increase	O
coverage	O
area	O
,	O
IEEE	O
802.11ax	O
(	O
Wi-Fi	O
6	O
)	O
provides	O
optional	O
support	O
for	O
,	O
,	O
and	O
guard	B-Protocol
intervals	I-Protocol
.	O
</s>
<s>
The	O
shorter	O
guard	B-Protocol
interval	I-Protocol
results	O
in	O
a	O
higher	O
packet	O
error	O
rate	O
when	O
the	O
delay	O
spread	O
of	O
the	O
channel	O
exceed	O
the	O
guard	B-Protocol
interval	I-Protocol
and/or	O
if	O
timing	O
synchronization	O
between	O
the	O
transmitter	O
and	O
receiver	O
is	O
not	O
precise	O
.	O
</s>
<s>
A	O
scheme	O
could	O
be	O
developed	O
to	O
work	O
out	O
whether	O
a	O
short	O
guard	B-Protocol
interval	I-Protocol
would	O
be	O
of	O
benefit	O
to	O
a	O
particular	O
link	O
.	O
</s>
<s>
To	O
reduce	O
complexity	O
,	O
manufacturers	O
typically	O
only	O
implement	O
a	O
short	O
guard	B-Protocol
interval	I-Protocol
as	O
a	O
final	O
rate	O
adaptation	O
step	O
when	O
the	O
device	O
is	O
running	O
at	O
its	O
highest	O
data	O
rate	O
.	O
</s>
