<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
repeat-accumulate	B-Error_Name
codes	I-Error_Name
(	O
RA	O
codes	O
)	O
are	O
a	O
low	O
complexity	O
class	O
of	O
error-correcting	B-Error_Name
codes	I-Error_Name
.	O
</s>
<s>
In	O
an	O
RA	O
code	O
,	O
an	O
information	O
block	O
of	O
length	O
is	O
repeated	O
times	O
,	O
scrambled	O
by	O
an	O
interleaver	O
of	O
size	O
,	O
and	O
then	O
encoded	O
by	O
a	O
rate	O
1	O
accumulator	B-General_Concept
.	O
</s>
<s>
The	O
accumulator	B-General_Concept
can	O
be	O
viewed	O
as	O
a	O
truncated	O
rate	O
1	O
recursive	O
convolutional	O
encoder	O
with	O
transfer	O
function	O
,	O
but	O
Divsalar	O
et	O
al	O
.	O
</s>
<s>
Systematic	O
IRA	O
codes	O
are	O
considered	O
a	O
form	O
of	O
LDPC	B-Error_Name
code	I-Error_Name
.	O
</s>
<s>
Litigation	O
over	O
whether	O
the	O
DVB-S2	O
LDPC	B-Error_Name
code	I-Error_Name
is	O
a	O
form	O
of	O
IRA	O
code	O
is	O
ongoing	O
.	O
</s>
