Iterative interference cancellation using mixed feedback weights and stabilizing step sizes
View Patent ↗A receiver is configured for canceling intra-cell and inter-cell interference in coded, multiple-access, spread-spectrum transmissions that propagate through frequency-selective communication channels. The receiver employs iterative symbol-estimate weighting, subtractive cancellation with a stabilizing step-size, and mixed-decision symbol estimates. Receiver embodiments may be implemented explicitly in software or programmed hardware, or implicitly in standard Rake-based hardware either within the Rake (i.e., at the finger level) or outside the Rake (i.e., at the user or subchannel symbol level).
1. An interference canceller configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the canceller comprising
a stabilizing step size module configured to calculate a stabilizing step size having a magnitude that is a function of at least a received signal,
the stabilizing step-size module configured for weighting an error signal with the stabilizing step size,
wherein the stabilizing step size module is configured to calculate the stabilizing step size as a function of the received signal and a synthesized received signal,
wherein the error signal is calculated as a difference between the received signal and the synthesized received signal.
2. An interference canceller configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the canceller comprising
a stabilizing step size module configured to calculate a stabilizing step size having a magnitude that is a function of at least a received signal,
the stabilizing step-size module configured for weighting an error signal with the stabilizing step size,
wherein the stabilizing step size module is configured to calculate the stabilizing step size as a function of the received signal and a synthesized received signal,
wherein the stabilizing step size is characterized by
μ
[
i
]
=
(
q
_
-
RF
Γ
[
i
]
b
_
^
[
i
]
)
H
(
q
_
-
RF
Γ
[
i
]
b
_
^
[
i
]
)
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
H
R
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
wherein μ [i] is a stabilizing step size after an i th iteration of the interference canceller; q is a received signal vector produced from processing the received signal by a Rake receiver, combining, and despreading;
b
_
^
[
i
]
is a vector containing all symbol decisions after the i th iteration of the interference canceller; R is a received-signal correlation matrix; F is an implementation matrix that is either an identity matrix or a transmit-signal correlation matrix; Γ (i) is a diagonal soft-weighting matrix that weights the elements of
b
_
^
[
i
]
;
and the superscript H denotes complex-conjugate matrix transposition.
3. An interference canceller configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the canceller comprising
a stabilizing step size module configured to calculate a stabilizing step size having a magnitude that is a function of at least a received signal,
the stabilizing step-size module configured for weighting an error signal with the stabilizing step size,
wherein the stabilizing step size module is configured to calculate the stabilizing step size as a ratio of distance measurements between a received signal and at least one synthesized received signal.
4. The interference canceller recited in claim 3 , wherein the stabilizing step size module is configured for:
calculating a first error vector for evaluating a first error signal as a difference between the received signal and a first synthesized received signal; employing a Rake receiver for resolving the first error signal onto a signal basis for all symbol sources in a channel for producing a first plurality of resolved signals, combining the plurality of resolved signals to produce a combined signal, and despreading the combined signal into a column vector;
calculating a second error vector as a difference between the received signal and the second synthesized received signal, employing a Rake receiver for resolving the second error signal onto a signal basis for all symbol sources in the channel for producing a second plurality of resolved signals, combining the second plurality of resolved signals for producing a second combined signal, and despreading the second combined signal into a column vector;
scaling the first error vector with soft weights for producing a weighted first error vector, evaluating an inner product between this weighted first error vector and the second error vector, and employing the inner product in the numerator; and
producing a synthesized received signal calculated from modeling a transmitted version of the first error vector, employing a signal basis for all symbol sources in the channel for producing a resolved composite signal, producing a square magnitude of the resolved composite signal, and integrating the square magnitude to calculate the denominator.
5. The interference canceller recited in claim 3 , wherein the stabilizing step size is characterized by
μ
[
i
]
=
(
q
_
-
R
Γ
[
i
]
F
Γ
[
i
]
b
_
^
[
i
]
)
H
Γ
[
i
]
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
H
(
Γ
[
i
]
)
H
R
Γ
[
i
]
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
wherein, μ [i] is a stabilizing step size after an i th iteration of the interference canceller; q is a received signal vector produced from processing the received signal by a Rake receiver, combining, and despreading; {circumflex over (b)} [i] is a vector containing all symbol decisions after the i th iteration of the interference canceller; R is a received-signal correlation matrix; F is an implementation matrix that is either an identity matrix or a transmit-signal correlation matrix; Γ [i] is a diagonal soft-weighting matrix that weights the elements of {circumflex over (b)} [i] ; and the superscript H denotes complex-conjugate matrix transposition.
6. An interference canceller configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the canceller comprising
a stabilizing step size module configured to calculate a stabilizing step size having a magnitude that is a function of at least a received signal,
the stabilizing step-size module configured for weighting an error signal with the stabilizing step size,
wherein the stabilizing step size module is configured for employing a plurality of methods for calculating the stabilizing step.
7. An interference canceller configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the canceller comprising
a stabilizing step size module configured to calculate a stabilizing step size having a magnitude that is a function of at least a received signal,
the stabilizing step-size module configured for weighting an error signal with the stabilizing step size,
wherein the stabilizing step size module is configured for calculating the stabilizing step as a function of channel-quality parameters.
8. The interference canceller recited in claim 7 , wherein the stabilizing step size is characterized by
μ
=
max
{
C
,
(
max
(
s
)
,
l
α
(
s
)
,
l
p
∑
s
=
0
B
-
1
∑
l
=
0
L
(
s
)
-
1
α
(
s
)
,
l
p
)
r
}
,
where μ is a stabilizing step size fixed for every iteration, B is a number of base stations, L (s) is a number of multipaths from an s th base station, α (s),l is a multipath gain corresponding to an l th path from an s th base station, max { } denotes a maximum function, and C, p, and r are non-negative constants.
9. An interference canceller configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the canceller comprising
a stabilizing step size module configured to calculate a stabilizing step size having a magnitude that is a function of at least a received signal,
the stabilizing step-size module configured for weighting an error signal with the stabilizing step size,
wherein the stabilizing step size module is configured to set the stabilizing step equal to a predetermined fixed value.
10. An interference cancellation method configured for
computing interference-cancelled symbol estimates and
applying stabilizing step sizes to an error signal during each of at least one iteration,
wherein applying stabilizing step sizes comprises providing for calculating a stabilizing step size having a magnitude that is a function of at least a received signal, and
wherein providing for calculating a stabilizing step size comprises calculating the stabilizing step size as a function of the received signal and a synthesized received signal,
wherein the error signal is calculated as a difference between the received signal and the synthesized received signal.
11. An interference cancellation method configured for
computing interference-cancelled symbol estimates and
applying stabilizing step sizes to an error signal during each of at least one iteration,
wherein applying stabilizing step sizes comprises providing for calculating a stabilizing step size having a magnitude that is a function of at least a received signal, and
wherein providing for calculating a stabilizing step size comprises calculating the stabilizing step size as a function of the received signal and a synthesized received signal,
wherein providing for calculating a stabilizing step size comprises producing the stabilizing step size characterized by
μ
[
i
]
=
(
q
_
-
RF
Γ
[
i
]
b
_
^
[
i
]
)
H
(
q
_
-
RF
Γ
[
i
]
b
_
^
[
i
]
)
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
H
R
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
wherein μ [i] is a stabilizing step size after an i th iteration of the interference cancellation method; q is a received signal vector produced from processing the received signal by a Rake receiver, combining, and despreading; {circumflex over (b)} [i] is a vector containing all symbol decisions after the i th iteration of the interference cancellation method; R is a received-signal correlation matrix; F is an implementation matrix that is either an identity matrix or a transmit-signal correlation matrix; Γ (i) is a diagonal soft-weighting matrix that weights the elements of {circumflex over (b)} [i] and the superscript H denotes complex-conjugate matrix transposition.
12. An interference cancellation method configured for
computing interference-cancelled symbol estimates and
applying stabilizing step sizes to an error signal during each of at least one iteration,
wherein applying stabilizing step sizes comprises providing for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein providing for calculating a stabilizing step size is configured to calculate the stabilizing step size as a ratio of distance measurements between a received signal and at least one synthesized received signal.
13. The method recited in claim 12 , wherein the ratio comprises a numerator and a denominator, wherein providing for calculating a stabilizing step size is configured for:
calculating a first error vector for evaluating a first error signal as a difference between the received signal and a first synthesized received signal;
employing a Rake receiver for resolving the first error signal onto a signal basis for all symbol sources in a channel for producing a first plurality of resolved signals, combining the plurality of resolved signals to produce a combined signal, and despreading the combined signal into a column vector;
calculating a second error vector as a difference between the received signal and the second synthesized received signal, employing a Rake receiver for resolving the second error signal onto a signal basis for all symbol sources in the channel for producing a second plurality of resolved signals, combining the second plurality of resolved signals for producing a second combined signal, and despreading the second combined signal into a column vector;
scaling the first error vector with soft weights for producing a weighted first error vector, evaluating an inner product between this weighted first error vector and the second error vector, and employing the inner product in the numerator; and
producing a synthesized received signal calculated from modeling a transmitted version of the first error vector, employing a signal basis for all symbol sources in the channel for producing a resolved composite signal, producing a square magnitude of the resolved composite signal, and integrating the square magnitude to calculate the denominator.
14. The method recited in claim 12 , wherein providing for calculating a stabilizing step size is configured to produce a stabilizing step size characterized by
μ
[
i
]
=
(
q
_
-
R
Γ
[
i
]
F
Γ
[
i
]
b
_
^
[
i
]
)
H
Γ
[
i
]
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
H
(
Γ
[
i
]
)
H
R
Γ
[
i
]
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
wherein μ [i] is a stabilizing step size after an i th iteration of the interference cancellation method; q is a received signal vector produced from processing the received signal by a Rake receiver, combining, and despreading; {circumflex over (b)} [i] is a vector containing all symbol decisions after the i th iteration of the interference cancellation method; R is a received-signal correlation matrix; F is an implementation matrix that is either an identity matrix or a transmit-signal correlation matrix; Γ (i) is a diagonal soft-weighting matrix that weights the elements of {circumflex over (b)} [i] and the superscript H denotes complex-conjugate matrix transposition.
15. An interference cancellation method configured for
computing interference-cancelled symbol estimates and
applying stabilizing step sizes to an error signal during each of at least one iteration,
wherein applying stabilizing step sizes comprises providing for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein providing for calculating a stabilizing step size comprises a plurality of methods for calculating the stabilizing step.
16. An interference cancellation method configured for
computing interference-cancelled symbol estimates and
applying stabilizing step sizes to an error signal during each of at least one iteration,
wherein applying stabilizing step sizes comprises providing for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein providing for calculating a stabilizing step size is configured for employing a function of channel-quality parameters to calculate the stabilizing step.
17. The method recited in claim 16 , wherein the stabilizing step size is characterized by
μ
=
max
{
C
,
(
max
(
s
)
,
l
α
(
s
)
,
l
p
∑
s
=
0
B
-
1
∑
l
=
0
L
(
s
)
-
1
α
(
s
)
,
l
p
)
r
}
,
where μ is a stabilizing step size fixed for every iteration, B is a number of base stations, L (s) is a number of multipaths from an s th base station, α (s),l is a multipath gain corresponding to an l th path from an s th base station, max { } denotes a maximum function, and C, p, and r are non-negative constants.
18. An interference cancellation method configured for
computing interference-cancelled symbol estimates and
applying stabilizing step sizes to an error signal during each of at least one iteration,
wherein applying stabilizing step sizes comprises providing for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein calculating the stabilizing step is configured to set the stabilizing step equal to a predetermined fixed value.
19. An interference cancellation system configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the system comprising
a stabilizing step size means,
wherein the stabilizing step-size means comprises a step size calculation means configured for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein the step size calculation means is configured to calculate the stabilizing step size as a function of the received signal and a synthesized received signal,
wherein the step size calculation means is configured to evaluate the error signal as a difference between the received signal and the synthesized received signal.
20. An interference cancellation system configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the system comprising
a stabilizing step size means,
wherein the stabilizing step-size means comprises a step size calculation means configured for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein the step size calculation means is configured to calculate the stabilizing step size as a function of the received signal and a synthesized received signal,
wherein the stabilizing step size is characterized by
μ
[
i
]
=
(
q
_
-
RF
Γ
[
i
]
b
_
^
[
i
]
)
H
(
q
_
-
RF
Γ
[
i
]
b
_
^
[
i
]
)
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
H
R
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
wherein μ [i] is a stabilizing step size after an i th iteration of the interference cancellation system; q is a received signal vector produced from processing the received signal by a Rake receiver, combining, and despreading; {circumflex over (b)} [i] is a vector containing all symbol decisions after the i th iteration of the interference cancellation system; R is a received-signal correlation matrix; F is an implementation matrix that is either an identity matrix or a transmit-signal correlation matrix; Γ (i) is a diagonal soft-weighting matrix that weights the elements of and {circumflex over (b)} [i] the superscript H denotes complex-conjugate matrix transposition.
21. An interference cancellation system configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the system comprising
a stabilizing step size means,
wherein the stabilizing step-size means comprises a step size calculation means configured for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein the step size calculation means is configured to calculate the stabilizing step size as a ratio of distance measurements between a received signal and at least one synthesized received signal.
22. The system recited in claim 21 , wherein the ratio comprises a numerator and a denominator, the step size calculation means configured for:
calculating a first error vector for evaluating a first error signal as a difference between the received signal and a first synthesized received signal; employing a Rake receiver for resolving the first error signal onto a signal basis for all symbol sources in a channel for producing a first plurality of resolved signals, combining the plurality of resolved signals to produce a combined signal, and despreading the combined signal into a column vector;
calculating a second error vector as a difference between the received signal and the second synthesized received signal, employing a Rake receiver for resolving the second error signal onto a signal basis for all symbol sources in the channel for producing a second plurality of resolved signals, combining the second plurality of resolved signals for producing a second combined signal, and despreading the second combined signal into a column vector;
scaling the first error vector with soft weights for producing a weighted first error vector, evaluating an inner product between this weighted first error vector and the second error vector, and employing the inner product in the numerator; and
producing a synthesized received signal calculated from modeling a transmitted version of the first error vector, employing a signal basis for all symbol sources in the channel for producing a resolved composite signal, producing a square magnitude of the resolved composite signal, and integrating the square magnitude to calculate the denominator.
23. The system recited in claim 21 , wherein the stabilizing step size is characterized by
μ
[
i
]
=
(
q
_
-
R
Γ
[
i
]
F
Γ
[
i
]
b
_
^
[
i
]
)
H
Γ
[
i
]
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
H
(
Γ
[
i
]
)
H
R
Γ
[
i
]
(
q
_
-
R
Γ
[
i
]
b
_
^
[
i
]
)
wherein, μ [i] is a stabilizing step size after an i th iteration of the interference cancellation system; q is a received signal vector produced from processing the received signal by a Rake receiver, combining, and despreading; {circumflex over (b)} [i] is a vector containing all symbol decisions after the i th iteration of the interference cancellation system; R is a received-signal correlation matrix; F is an implementation matrix that is either an identity matrix or a transmit-signal correlation matrix; Γ (i) is a diagonal soft-weighting matrix that weights the elements of {circumflex over (b)} [i] and the superscript H denotes complex-conjugate matrix transposition.
24. An interference cancellation system configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the system comprising
a stabilizing step size means,
wherein the stabilizing step-size means comprises a step size calculation means configured for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein the step size calculation means is configured for employing a plurality of methods for calculating the stabilizing step.
25. An interference cancellation system configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the system comprising
a stabilizing step size means,
wherein the stabilizing step-size means comprises a step size calculation means configured for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein the step size calculation means is configured for calculating the stabilizing step as a function of channel-quality parameters.
26. The system recited in claim 25 , wherein the stabilizing step size is characterized by
μ
=
max
{
C
,
(
max
(
s
)
,
l
α
(
s
)
,
l
p
∑
s
=
0
B
-
1
∑
l
=
0
L
(
s
)
-
1
α
(
s
)
,
l
p
)
r
}
,
where μ [i] is a stabilizing step size fixed for every iteration, B is a number of base stations, L (S) is a number of multi paths from an s th base station, α (s),l is a multipath gain corresponding to an l th path from an s th base station, max { } denotes a maximum function, and C, p, and r are non-negative constants.
27. An interference cancellation system configured for computing interference-cancelled symbol estimates and performing processing during each of at least one iteration, the system comprising
a stabilizing step size means,
wherein the stabilizing step-size means comprises a step size calculation means configured for calculating a stabilizing step size having a magnitude that is a function of at least a received signal,
wherein the step size calculation means is configured to set the stabilizing step equal to a predetermined fixed value.