Method of receiver processing of CDMA signals in a CDMA system
View Patent ↗The method of receiver processing of CDMA signals in a CDMA system includes first converting a received signal in the time domain to a received signal in the frequency domain, and equalizing the received signal in the frequency domain using a set of frequency domain weights. The equalized received signal in the frequency domain is converted to an equalized received signal in the time domain. The set of frequency domain weights are adaptively adjusted at a symbol rate of the received signal in the time domain based on an error signal produced from the received signal in the frequency domain and a frequency domain representation of a known pilot signal of the CDMA system.
1. A method of receiver processing of CDMA signals in a CDMA system, comprising:
first converting, by at least one receiver, a received signal in the time domain to a received signal in the frequency domain;
adaptively adjusting frequency domain weights based on an error signal produced from the received signal in the frequency domain and a frequency domain representation of a known pilot signal of the CDMA system, at a symbol rate of the received signal in the time domain;
equalizing the received signal in the frequency domain using the set of adaptively adjusted frequency domain weights; and
second converting the equalized received signal in the frequency domain to an equalized received signal in the time domain;
wherein the adaptively adjusting step includes,
generating the error signal in the frequency domain to represent a difference of the equalized received signal from the known pilot signal.
2. The method of claim 1 , wherein the adaptively adjusting further comprises:
applying a step size matrix to the error signal to generate the set of frequency domain weights, the step size matrix providing a respective amount to adjust each weight of the set of frequency domain weights based on a spectrum of received signal in the frequency domain.
3. The method of claim 2 , wherein the generating comprises:
estimating a pilot symbol amplitude from the equalized received signal in the time domain;
determining a difference in amplitude between the estimated pilot symbol amplitude and a known amplitude of the known pilot signal as an error magnitude;
multiplying the received signal in the frequency domain by the known pilot signal in the frequency domain to obtain an error direction; and
multiplying the error magnitude and the error direction to obtain the error signal.
4. The method of claim 3 , further comprising:
determining the step size matrix according to the following expression,
D l =μP j −1
P j =(1−β) P j−1 +βdiag(| FFT{r j−1 }| 2 )
where r is the received signal in the time domain, diag (•) denotes a diagonal matrix, and β is a forgetting factor constant.
5. The method of claim 2 , further comprising:
determining the step size matrix according to the following expression,
D l =μP j −1
P j =(1−β) P j−1 +βdiag(| FFT{r j−1 }| 2 )
where r is the received signal in the time domain, diag (•) denotes a diagonal matrix, and β is a forgetting factor constant.
6. The method of claim 1 , wherein
first converting converts a vector yj of a received signal rj and the previous received signal rj−1 where
y
j
=
[
r
j
-
1
r
j
]
,
each of the received signal rj and the previous received signal rj−1 having E elements;
the equalizing calculates a product of the vector yj and the set of weights to the second converting converts a second E of the 2E elements in the vector z to the time domain.
7. The method of claim 6 , wherein the adaptively adjusting comprises:
generating the error signal g j in the frequency domain to represent the difference of the equalized received signal from the known pilot signal according to the following expression,
g
_
j
=
e
j
(
conj
(
y
_
)
j
⊙
FFT
(
p
j
′
)
)
where
e
j
=
GA
p
-
〈
p
j
,
z
j
〉
,
p
k
′
=
[
0
E
×
1
p
k
]
,
and p k represents the known pilot signal, p j ,z j represents the conventional dot product or an accumulation of chips for one symbol in the equalized received signal in the time domain, and GA p represents a magnitude of the known pilot signal; and
applying a step size matrix Dj to the error signal to generate the set of frequency domain weights, the step size matrix providing a respective amount to adjust each weight of the set of frequency domain weights based on a spectrum of received signal in the frequency domain.
8. The method of claim 7 , further comprising:
determining the step size matrix Dj according to the following expression,
D l =μP j −1
P j =(1−β) P j−1 +βdiag(| FFT{r j−1 }| 2 )
where r is the received signal in the time domain, diag (•) denotes a diagonal matrix, and β is a forgetting factor constant.
9. The method of claim 1 , wherein
the CDMA system is a multiple-input multiple-output (MIMO) CDMA system having a known pilot signal associated with each transmit antenna;
the first converting converts a plurality of received signals in the time domain to received signals in the frequency domain; and for each known pilot signal,
the equalizing equalizes the received signals in the frequency domain using a set of frequency domain weights associated with each received signal; and the method further includes,
combining the equalized received signals; and wherein
the second converting converts the combined equalized received signal in the frequency domain to a combined equalized received signal in the time domain; and
the adaptively adjusting adaptively adjusts the set of frequency domain weights associated with each received signal at a symbol rate of the received signal in the time domain based on an error signal produced from the received signal in the frequency domain and a frequency domain representation of the known pilot signal.
10. The method of claim 9 , wherein, for each known pilot signal, the adaptively adjusting comprises:
generating the error signal associated with each received signal; and
applying a step size matrix to the error signal to generate the set of frequency domain weights, the step size matrix providing a respective amount to adjust each weight of the set of frequency domain weights based on a spectrum of received signal in the frequency domain.
11. The method of claim 10 , wherein the applying comprises:
determining the step size matrix D as,
D
=
μ
(
U
¨
D
)
-
1
,
where
U
¨
D
=
[
P
1
,
1
P
1
,
2
…
P
1
,
N
P
1
,
2
*
P
2
,
2
⋰
⋮
P
1
,
2
*
P
2
,
N
*
…
p
N
,
N
]
P
i
,
n
(
j
+
1
)
=
(
1
-
β
)
P
i
,
n
(
j
)
+
β
diag
(
y
_
i
⊙
y
_
n
)
where N is the number of receive antennas, indices i and n each index a particular receive antenna, for an antenna j,
y
_
j
=
FFT
(
y
j
)
,
y
j
=
[
r
j
-
1
r
j
]
r j is a current received signal in the time domain and r j−1 is a previous received signal in the time domain, diag (•) denotes a diagonal matrix, and β is a forgetting factor constant.
12. A method of receiver processing of CDMA signals in a CDMA system, comprising:
applying, by at least one receiver, an LMS (least mean squares) algorithm to a received CDMA signal in the frequency domain where weights of the LMS algorithm are updated in the frequency domain based on an error signal at a symbol rate of the received CDMA signal, wherein the error signal is generated in the frequency domain to represent a difference of an equalized received signal from a known pilot signal of the CDMA system.
13. The method of claim 12 , wherein the applying [step] applies the LMS algorithm trained using the known pilot signal.
14. The method of claim 12 , wherein a step size adjustment of the LMS algorithm is preformed using step size matrix providing a respective amount to adjust each weight of the set of frequency domain weights based on a spectrum of received signal in the frequency domain.