BICM decoding in the presence of co-channel interference
View Patent ↗Systems and methods are provided for computing soft information for digital information based on a received signal, where the received signal suffers from noise and interference. A receiver that decodes the received signal may estimate channel information, such as the channel gain, associated with the interfering source. The receiver may also obtain modulation information through a backbone network or by decoding control information transmitted by the interfering source. Using the modulation information and the channel information, the receiver may estimate the effect that interference has on the received signal, and may compute soft information (e.g., a log-likelihood ratio) for the digital information.
1. A method of computing soft information for use in estimating digital information from an intended source, the method comprising:
determining modulation information associated with at least one interfering source;
estimating intended channel information associated with the intended source;
determining intended modulation information associated with the intended source;
receiving a signal corresponding to the digital information, wherein the signal includes an interference signal from the at least one interfering source; and
computing soft information for the digital information from the signal based on the modulation information, the intended channel information and the intended modulation information.
2. The method of claim 1 , further comprising:
receiving a pilot signal from a channel associated with the intended source,
wherein estimating the intended channel information comprises determining a magnitude and phase of the received pilot signal, and
wherein determining the intended modulation information comprises decoding the received pilot signal to identify a modulation scheme used by the intended source.
3. The method of claim 1 , wherein determining the modulation information comprises:
receiving a pilot signal from a channel associated with the at least one interfering source;
analyzing a pseudo-noise (PN) sequence associated with the pilot signal to determine that the pilot signal was transmitted by the at least one interfering source; and
decoding the pilot signal to identify a modulation scheme used by the at least one interfering source.
4. The method of claim 1 , wherein determining the modulation information comprises:
identifying the modulation information from a frequency band associated with the at least one interfering source, wherein the signal corresponding to the digital information uses a larger frequency band than the frequency band associated with the at least one interfering source.
5. The method of claim 1 , wherein determining the modulation information comprises:
receiving control information associated with the at least one interfering source; and
performing DL-MAP decoding on the received control information.
6. The method of claim 1 , wherein determining the modulation information comprises obtaining the modulation information from a backbone network.
7. The method of claim 1 , wherein computing soft information comprises computing a log-likelihood ratio (LLR) for an ith bit in the digital information according to:
LLR
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=
log
(
∑
x
∈
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l
i
(
1
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,
s
∈
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exp
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)
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,
where i is an integer, y is the received signal, h is an intended channel gain associated with the intended source, g is an interference channel gain associated with the at least one interfering source, x is at least a portion of the digital information, l i is a bit position of the ith bit, k i is a sampling time of the ith bit, s is the interference signal, and σ z 2 is a power of noise.
8. The method of claim 1 , wherein computing soft information comprises computing a log-likelihood ratio (LLR) for an ith bit in the digital information according to:
LLR
i
=
1
σ
z
2
[
min
x
∈
X
l
i
(
0
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,
s
∈
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where i is an integer, y is the received signal, h is an intended channel gain associated with the intended source, g is an interference channel gain associated with the at least one interfering source, x is at least a portion of the digital information, l i is a bit position of the ith bit, k i is a sampling time of the ith bit, s is the interference signal, and σ z 2 is a power of noise.
9. The method of claim 1 , wherein computing soft information comprises computing a log-likelihood ratio (LLR) for an ith bit in the digital information according to:
LLR
i
=
log
(
∑
x
∈
X
l
i
(
1
)
,
s
∈
S
exp
(
-
y
k
i
-
h
k
i
x
2
σ
z
2
+
σ
g
2
s
2
)
)
-
log
(
∑
x
∈
X
l
i
(
0
)
,
s
∈
S
exp
(
-
y
k
-
h
k
i
x
2
σ
z
2
+
σ
g
2
s
2
)
)
,
where i is an integer, y is the received signal, h is an intended channel gain associated with the intended source, σ g 2 is an average magnitude square of an interference channel gain associated with the at least one interfering source, x is at least a portion of the digital information, l i is a bit position of the ith bit, k i is a sampling time of the ith bit, s is the interference signal, and σ z 2 is a power of noise.
10. An apparatus for computing soft information to estimate digital information from an intended source, the apparatus comprising:
computational logic circuitry to:
determine modulation information associated with at least one interfering source;
estimate intended channel information associated with the intended source; and
determine intended modulation information associated with the intended source
an input interface to receive a signal corresponding to the digital information, wherein the signal includes an interference signal from the at least one interfering source; and
a soft bit-metric calculator to compute soft information for the digital information from the signal based on the modulation information, the intended channel information and the intended modulation information.
11. The apparatus of claim 10 , wherein the computational logic is further configured to:
estimate the intended channel information by determining a magnitude and phase of a pilot signal received from a channel associated with the intended source; and
determine the intended modulation information by decoding the received pilot signal to identify a modulation scheme used by the intended source.
12. The apparatus of claim 10 , wherein the computational logic is configured to determine modulation information by:
analyzing a pseudo-noise (PN) sequence associated with a pilot signal to determine that the pilot signal was transmitted by the at least one interfering source; and
decoding the pilot signal to identify a modulation scheme used by the at least one interfering source.
13. The apparatus of claim 10 , wherein the computational logic is configured to determine the modulation information by decoding control information received from the at least one interfering source.
14. The apparatus of claim 10 , wherein the computational logic is configured to determine the modulation information by obtaining the modulation information from a backbone network.
15. The apparatus of claim 10 , wherein the soft bit-metric calculator computes a log-likelihood ratio (LLR) for each bit of the digital information.
16. The apparatus of claim 15 , wherein the soft bit-metric calculator computes the LLR for an ith bit in the digital information according to:
LLR
i
=
log
(
∑
x
∈
X
l
i
(
1
)
,
s
∈
S
exp
(
-
y
k
i
-
h
k
i
x
-
g
k
i
s
2
σ
z
2
)
)
-
log
(
∑
x
∈
X
l
i
(
0
)
,
s
∈
S
exp
(
-
y
k
i
-
h
k
i
x
-
g
k
i
s
2
σ
z
2
)
)
,
where i is an integer, y is the received signal, h is an intended channel gain associated with the intended source, g is an interference channel gain associated with the at least one interfering source, x is at least a portion of the digital information, l i is a bit position of the ith bit, k i is a sampling time of the ith bit, s is the interference signal, and σ z 2 is a power of noise.
17. The apparatus of claim 15 , wherein the soft bit-metric calculator computes the LLR for an ith bit in the digital information according to:
LLR
i
=
1
σ
z
2
[
min
x
∈
X
l
i
(
0
)
,
s
∈
S
{
y
k
i
-
h
k
i
x
-
g
k
i
s
2
}
-
min
x
∈
X
l
i
(
1
)
,
s
∈
S
{
y
k
i
-
h
k
i
x
-
g
k
i
s
2
}
]
,
where i is an integer, y is the received signal, h is an intended channel gain associated with the intended source, g is an interference channel gain associated with the at least one interfering source, x is at least a portion of the digital information, l i is a bit position of the ith bit, k i is a sampling time of the ith bit, s is the interference signal, and σ z 2 is a power of noise.
18. The apparatus of claim 15 , wherein the soft bit-metric calculator computes the LLR for an ith bit in the digital information according to:
LLR
i
=
log
(
∑
x
∈
X
l
i
(
1
)
,
s
∈
S
exp
(
-
y
k
i
-
h
k
i
x
2
σ
z
2
+
σ
g
2
s
2
)
)
-
log
(
∑
x
∈
X
l
i
(
0
)
,
s
∈
S
exp
(
-
y
k
i
-
h
k
i
x
2
σ
z
2
+
σ
g
2
s
2
)
)
,
where i is an integer, y is the received signal, h is an intended channel gain associated with the intended source, σ g 2 is an average magnitude square of an interference channel gain associated with the at least one interfering source, x is at least a portion of the digital information, l i is a bit position of the ith bit, k i is a sampling time of the ith bit, s is the interference signal, and σ z 2 is a power of noise.