Linear approximation of the max* operation for log-map decoding
View Patent ↗A decoder for a wireless communication device comprising a calculator for calculating the modulo of a linear approximation of a MAX* function; and a selector for selecting a MAX* output value from the group a(n)mod F, b(n)mod F, and the calculated modulo based upon a determination as to whether a predetermined threshold value for |a(n)−b(n)| has been met, where a(n) is a first state metric, b(n) is a second state metric, C is the predetermined threshold value and F is a value greater than |a(n)−b(n)|.
1. A decoder for a wireless communication device comprising:
a calculator for calculating the modulo of a linear approximation of a MAX* function using:
(
a
(
n
)
mod
F
+
(
(
b
(
n
)
mod
F
-
a
(
n
)
mod
F
)
mod
F
+
C
)
2
)
mod
F
;
and
a selector for selecting a MAX* output value from the group a(n)mod F, b(n)mod F, and the calculated modulo based upon a determination as to whether a predetermined threshold value for |a(n)−b(n)| has been met, where a(n) is a first state metric, b(n) is a second state metric, C is the predetermined threshold value and F is a value greater than |a(n)−b(n)|; wherein
the decoder is arranged to receive an information bit and to use the selected MAX* output value to decode the received information bit.
2. A decoder according to claim 1 , wherein the calculator is arranged to calculate the modulo of the linear approximation of the MAX* function using:
(
(
(
a
(
n
)
mod
F
+
C
)
mod
F
+
b
(
n
)
mod
F
2
)
mod
F
+
F
*
s
)
mod
F
,
where s is equal to [a(m) XOR b(m)] AND [((a(m) XOR a(m−1)) and ((b(m) XOR b(m−1)] and a(m) b(m) a(m−1) and b(m−1) are the most significant bits of a(n) b(n) a(n−1) and b(n−1) respectively.
3. A decoder according to claim 1 , wherein the determination is based upon the sign of (a(n)mod F−b(n)mod F−C)mod F and the sign of (b(n)mod F−a(n)mod F−C)mod F.
4. A decoder according to claim 1 , wherein the selector is arranged to select and output the modulo of the linear approximation of the MAX* function if the value |a(n)−b(n)| is less than the predetermined threshold value.
5. A decoder according to claim 1 , wherein the value of F is to the power of two.
6. A decoder according to claim 1 , wherein the selector is a multiplexer.
7. A decoder according to claim 1 , wherein the calculator is an add module that is arranged to receive a(n)mod F, b(n)mod F and C.
8. A method of decoding an information bit by a decoder using a MAX* value, the method comprising:
receiving an information bit by the decoder;
receiving by a selector, a first modulo state metric a(n)mod F, a second modulo state metric b(n)mod F and a predetermined threshold value C for |a(n)−b(n)|, where F is a value greater than |a(n)−b(n)|;
calculating by a calculator, the modulo of a linear approximation of a MAX* function using:
(
a
(
n
)
mod
F
+
(
(
b
(
n
)
mod
F
-
a
(
n
)
mod
F
)
mod
F
+
C
)
2
)
mod
F
;
selecting by the selector, a value from the group a(n)mod F, b(n)mod F, and the calculated modulo based upon a determination as to whether the predetermined threshold value C for |a(n)−b(n)| has been met; and
decoding by the decoder, the received information bit using the selected value.
9. A method according to claim 8 , wherein the modulo of the linear approximation of the MAX* function is calculated using:
(
(
(
a
(
n
)
mod
F
+
C
)
mod
F
+
b
(
n
)
mod
F
2
)
mod
F
+
F
*
s
)
mod
F
,
where s is equal to [a(m) XOR b(m)] AND [((a(m) XOR a(m−1)) AND ((b(m) XOR b(m−1)].