Soft sample scaling in a turbo decoder
View Patent ↗A receiver for iterative decoding of a received, encoded signal employs slot-based scaling of soft samples. Iterative decoding employs a constituent maximum a priori (MAP) decoder for each constituent encoding of information of the encoded signal. Root mean square (RMS) values for soft samples over a slot are selected for dynamic range scaling. Squared RMS values are combined and equal the squared RMS value for a frame multiplied by a control constant, and this relationship may be employed to derive scaling constants for each slot. Alternatively, the square root of the RMS value multiplied by a constant serves as an SNR estimator that may be employed to scale samples to reduce dynamic range and modify logarithmic correction values for max* term calculation during log-MAP decoding.
1. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot;
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein the scaling factor (1/c) is set as:
1
c
≈
4
*
0.798
*
SNR
2
+
1
0.65
*
(
2
q
-
1
-
1
)
*
RMS
i
=
M
i
RMS
i
,
where SNR is a signal-to-noise ratio value, M i is a constant for the ith slot, q is a number of bits defined by a digital quantizing method, and RMS i is the RMS value of the samples over the ith slot.
2. The invention of claim 1 , wherein, for step (b), the scaling factor is calculated using a scaling constant such that the RMS value of samples after scaling over a frame approximates a predefined value, wherein the frame comprises one or more slots.
3. The invention of claim 1 , wherein, for step (b), the scaling factor is a noise variance estimator.
4. The invention of claim 1 , wherein step (c) comprises the step of scaling the samples within the slot to adjust a dynamic range of the samples.
5. The invention of claim 1 , further comprising the steps of:
b1) estimating a noise variance as a function of the RMS value;
b2) generating a constant for each logarithmic correction term of log-MAP decoding using the estimated noise variance; and
b3) setting the scaling factor based on the constant.
6. The invention of claim 5 , wherein step (c) comprises the step of either (c1) adjusting the samples or (c2) adjusting one or more previously generated logarithmic correction terms based on the scaling factor for log-MAP decoding.
7. The invention of claim 1 , wherein step (c) comprises the step of either (c1) adjusting the samples or (c2) adjusting one or more previously generated logarithmic correction terms based on the scaling factor for log-MAP decoding.
8. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot;
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein the scaling factor (1/c) accounts for automatic gain control (AGC) and is set as:
1
c
=
F
i
E
(
ξ
i
)
RMS
i
=
F
i
(
1
3
K
∑
3
K
-
1
i
=
0
ξ
i
)
RMS
i
,
where F i is a constant for the slot, K is a number of samples per slot, RMS i is the RMS value of the samples over the ith slot, E(●) denotes mathematical “expected value of”, and ξ i is the sequence of input soft samples in the slot.
9. The invention of claim 8 , further comprising the steps of:
b1) estimating a noise variance as a function of the RMS value;
b2) generating a constant for each logarithmic correction term of log-MAP decoding using the estimated noise variance; and
b3) setting the scaling factor based on the constant.
10. The invention of claim 8 , wherein, for step (b), the scaling factor is calculated using a scaling constant such that the RMS value of samples over a frame approximates a predefined value, wherein the frame comprises one or more slots.
11. The invention of claim 8 , wherein, for step (b), the scaling factor is a noise variance estimator.
12. The invention of claim 8 , wherein step (c) comprises the step of scaling the samples within the slot to adjust a dynamic range of the samples.
13. The invention of claim 8 , wherein step (c) comprises the step of either (c1) adjusting the samples or (c2) adjusting one or more previously generated logarithmic correction terms based on the scaling factor for log-MAP decoding.
14. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot;
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein:
the scaling factor (1/c) accounts for DC offset signals present within the samples; and
the scaling factor (1/c) accounting for DC offset is set as:
1
c
=
G
i
RMS
i
-
[
E
(
ξ
i
)
]
2
=
G
i
RMS
i
-
(
1
3
K
∑
3
K
-
1
i
=
0
ξ
i
)
2
,
where G i is a control constant for the slot, K is a number of samples per slot, RMS i is the RMS value of the samples over the ith slot, E(●) denotes mathematical “expected value of”, and ξ i is the sequence of input soft samples in the slot.
15. The invention of claim 14 , further comprising the steps of:
b1) estimating a noise variance as a function of the RMS value;
b2) generating a constant for each logarithmic correction term of log-MAP decoding using the estimated noise variance; and
b3) setting the scaling factor based on the constant.
16. The invention of claim 14 , wherein, for step (b), the scaling factor is calculated using a scaling constant such that the RMS value of samples over a frame approximates a predefined value, wherein the frame comprises one or more slots.
17. The invention of claim 14 , wherein, for step (b), the scaling factor is a noise variance estimator.
18. The invention of claim 14 , wherein step (c) comprises the step of scaling the samples within the slot to adjust a dynamic range of the samples.
19. The invention of claim 14 , wherein step (c) comprises the step of either (c1) adjusting the samples or (c2) adjusting one or more previously generated logarithmic correction terms based on the scaling factor for log-MAP decoding.
20. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot wherein the RMS is approximately E[|ξ i | 2 ];
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein the scaling factor (1/c) is set as:
1
c
≈
H
i
E
(
ξ
i
)
,
where H i is a constant for a given slot, E(●) denotes mathematical “expected value of”, and ξ i is the sequence of input soft samples in the slot.
21. The invention of claim 20 , wherein, for step (b), the scaling factor is calculated using a scaling constant such that the RMS value of samples after scaling over a frame approximates a predefined value, wherein the frame comprises one or more slots.
22. The invention of claim 20 , wherein, for step (b), the scaling factor is a noise variance estimator.
23. The invention of claim 20 , wherein step (c) comprises the step of scaling the samples within the slot to adjust a dynamic range of the samples.
24. The invention of claim 20 , further comprising the steps of:
b1) estimating a noise variance as a function of the RMS value;
b2) generating a constant for each logarithmic correction term of log-MAP decoding using the estimated noise variance; and
b3) setting the scaling factor based on the constant.
25. The invention of claim 20 , wherein step (c) comprises the step of either (c1) adjusting the samples or (c2) adjusting one or more previously generated logarithmic correction terms based on the scaling factor for log-MAP decoding.
26. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot;
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein:
the scaling factor accounts for at least one of automatic gain control (AGC) and DC offset signals present within the samples; and
the scaling factor (1/c) accounting for AGC is set as:
1
c
=
F
i
E
(
ξ
i
)
RMS
i
=
F
i
(
1
3
K
∑
3
K
-
1
i
=
0
ξ
i
)
RMS
i
,
where F i is a constant for the slot, K is a number of samples per slot, RMS i is the RMS value of the samples over the ith slot, E(●) denotes mathematical “expected value of”, and ξ 1 is the sequence of input soft samples in the slot.
27. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot;
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein:
the scaling factor accounts for at least one of automatic gain control (AGC) and DC offset signals present within the samples; and
the scaling factor (1/c) accounting for DC offset is set as:
1
c
=
G
i
RMS
i
-
[
E
(
ξ
i
)
]
2
=
G
i
RMS
i
-
(
1
3
K
∑
3
K
-
1
i
=
0
ξ
i
)
2
,
where G i is a control constant for the slot, K is a number of samples per slot, RMS i is the RMS value of the samples over the ith slot, E(●) denotes mathematical “expected value of”, and ξ i is the sequence of input soft samples in the slot.
28. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot;
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein:
step (b) further comprises the steps of:
b1) estimating a noise variance as a function of the RMS value;
b2) generating a constant for each logarithmic correction term of log-MAP decoding using the estimated noise variance; and
b3) setting the scaling factor based on the constant;
the scaling factor accounts for at least one of automatic gain control (AGC) and DC offset signals present within the samples; and
the scaling factor (1/c) accounting for AGC is set as:
1
c
=
F
i
E
(
ξ
i
)
RMS
i
=
F
i
(
1
3
K
∑
3
K
-
1
i
=
0
ξ
i
)
RMS
i
,
where F i is a constant is a constant for the slot, RMS i is the RMS value of the samples over the ith slot, E(●) denotes mathematical “expected value of”, and ξ i is the sequence of input soft samples in the slot.
29. A method of scaling samples of an encoded signal iteratively decoded to generate decoded data, the method comprising the steps of:
(a) generating a root mean square (RMS) value for samples within a slot;
(b) calculating a scaling factor based on the RMS value of the slot; and
(c) scaling the input samples of the slot based on the scaling factor,
wherein the scaling factor accounts for at least one of automatic gain control (AGC) and DC offset signals present within the samples;
wherein:
step (b) further comprises the steps of:
b1) estimating a noise variance as a function of the RMS value; and
b2) generating a constant for each logarithmic correction term of log-MAP decoding using the estimated noise variance; and
b3) setting the scaling factor based on the constant;
the scaling factor (1/c) accounting for DC offset is set as:
1
c
=
G
i
RMS
i
-
[
E
(
ξ
i
)
]
2
=
G
i
RMS
i
-
(
1
3
K
∑
3
K
-
1
i
=
0
ξ
i
)
2
,
where G i is a control constant for the slot, K is a number of samples per slot, RMS i is the RMS value of the samples over the ith slot, E(●) denotes mathematical “expected value of”, and ξ i is the sequence of input soft samples in the slot.