Turbo decoder using parallel processing
View Patent ↗A method of decoding using a log posterior probability ratio L(u k ), which is a function of forward variable α (.) and backward variable β (.). The method comprises dividing the forward variable α (.) and the backward variable β (.) into, for example, two segments p and q, where p plus q equal the length of the code word U. The forward segments α (.) are parallel calculated, and the backward segments β (.) are parallel calculated. The ratio L(u k ) is calculated using the parallel calculated segments of α (.) and β (.).
1. A method of a turbo decoder using log A Posteriori Probability L(u k ), where L(u k )=f(α k (.), β k (.)), the method comprising:
dividing a forward variable α (.) and a backward variable β (.) into a plurality M of parallel segments of size p, q . . . w, where p+q, . . . +w equals the length of a coded word U;
simultaneous, parallel calculating the segments of forward variable α (.) of the code word U as follows:
α
1
(
.
)
,
…
,
α
p
(
.
)
starting
from
α
0
(
.
)
α
p
+
1
(
.
)
,
…
,
α
q
(
.
)
starting
from
α
p
(
.
)
⋮
α
w
+
1
(
.
)
,
…
,
α
K
(
.
)
starting
from
α
w
(
.
)
;
and the segments of the backward variable β (.) of the code word U as follows:
β
K
-
1
(
.
)
,
…
,
β
w
+
1
(
.
)
starting
from
β
K
(
.
)
β
w
(
.
)
,
…
,
β
v
+
1
(
.
)
starting
from
β
w
+
1
(
.
)
⋮
β
q
(
.
)
,
…
,
β
1
(
.
)
starting
from
β
q
+
1
(
.
)
;
and
calculating L(u k ) using the parallel calculated segments of α (.) and β (.).
2. The method according to claim 1 , wherein the segment sizes are set equal.
3. A signal receiver including a decoder performing the method according to claim 1 .
4. The method according to claim 1 , wherein the starting points α p (.), . . . , α w (.) are estimated, and the starting points β w+1 (.), . . . , β q+1 are estimated.
5. The method according to claim 4 , wherein the starting points for the forward variable are estimated from:
α
p
-
d
+
1
(
.
)
,
…
,
α
p
(
.
)
⋮
α
w
-
d
+
1
(
.
)
,
…
,
α
w
(
.
)
;
and
for the backward segments from:
β
w
+
d
(
.
)
,
…
,
β
w
+
1
(
.
)
⋮
β
q
+
d
(
.
)
,
…
,
β
q
+
1
(
.
)
where d is an arbitrary amount of time steps.
6. The method according to claim 5 , wherein d is in the range of 1 to 20.
7. The method according to claim 5 , wherein d is in the range of 15 to 20.
8. The method according to claim 5 , wherein the probabilities of the first states for estimating the starting points are uniform random variables.
9. The method according to claim 5 , wherein the first states for estimating the starting points are a predetermined state.
10. The method according to claim 5 , wherein the first states for estimating the starting point is one divided by the number of possible states.
11. A method of decoding using a log A Posteriori Probability ratio L(u k ) where L(u k )=f(α k (.), β k (.) ), the method comprising:
dividing a forward variable α (.) and a backward variable β (.) into two segments p and q where p+q equals the length of the code word U;
parallel calculating the forward segments:
α 1 (.), . . . ,α p (.) starting from a known α 0 (.) and
α p+1 (.), . . . ,α k (.) starting from an estimated α p (.);
parallel calculating the backward segments:
β K−1 (.), . . . , β q+1 (.) starting from a known β K (.) and
β q (.), . . . , β 1 (.) starting from an estimated β q+1 (.); and
calculating L(u k ) using the parallel calculated segments of α (.) and β (.).
wherein the forward and backward segments are calculated simultaneously.
12. A signal receiver including a decoder performing the method according to claim 11 .
13. A method according to claim 11 , wherein the estimated starting point α p (.) is estimated from state probabilities α p−d+1 (.), . . . , α p (.), and the estimated starting point β q+1 (.) is estimated from state probabilities for β q+d (.), . . . , β q+1 (.).
14. A method according to claim 13 , wherein d is in the range of 1 to 20.
15. A method according to claim 13 , wherein d is in the range of 15 to 20.
16. A method according to claim 13 , wherein the probabilities of the first states for estimating the starting points are uniform random variables.
17. A method according to claim 13 , wherein the first states for estimating the starting points are a predetermined state.
18. A method according to claim 13 , wherein the first states for estimating the starting point is one divided by the number of possible states.