Method and system for baseband predistortion linearization in multi-channel wideband communication systems
An efficient baseband predistortion linearization method for reducing the spectral regrowth and compensating memory effects in wideband communication systems using effective multiplexing modulation technique such as wideband code division multiple access and orthogonal frequency division multiplexing is disclosed. The present invention is based on the method of piecewise pre-equalized lookup table based predistortion, which is a cascade of a lookup table predistortion and piecewise pre-equalizers.
1. A method of reducing adjacent channel power ratio in a multi-channel wideband communication system, the method comprising:
generating a pre-distorted input signal by multiplying a baseband input signal and a polynomial predistortion coefficient from plurality of polynomial predistortion coefficients, wherein the polynomial predistortion coefficient is based on an absolute value of the input signal multiplied by the number of predistortion coefficients in the plurality of predistortion coefficients, rounded to the nearest integer; and
pre-equalizing the pre-distorted input signal using one or more polynomial pre-equalization coefficients, the one or more polynomial pre-equalization coefficients corresponding to memory effects in a power amplifier of the communication system.
2. The method of claim 1 , wherein the polynomial predistortion coefficient is calculated using the following equation:
F
m
(
u
(
n
-
k
)
)
=
∑
p
=
1
P
b
2
p
-
1
·
u
(
n
-
k
)
2
(
p
-
1
)
,
wherein 2p−1 is a polynomial order and b is a complex coefficient corresponding to the polynomial order.
3. The method of claim 2 , wherein the pre-distorted input signal is pre-equalized using the following equation:
z
(
n
)
=
∑
k
=
0
K
-
1
∑
l
=
1
L
w
k
,
2
l
-
1
·
u
(
n
)
2
(
l
-
1
)
×
∑
p
=
1
P
b
2
p
-
1
·
u
(
n
-
k
)
·
u
(
n
-
k
)
2
(
p
-
1
)
,
wherein w k,l is a k-th tap and 1-th order coefficient.
4. The method of claim 1 , wherein the one or more polynomial pre-equalization coefficients correspond to filter coefficients of a finite impulse response filter.
5. The method of claim 1 , wherein the one or more polynomial pre-equalization coefficients correspond to filter coefficients of an infinite impulse response filter.
6. The method of claim 1 , further comprising:
upconverting the pre-equalized signal to radio frequency; and
outputting the upconverted signal to the power amplifier.
7. The method of claim 6 , further comprising:
downconverting the amplified signal to baseband;
comparing the baseband amplified signal to the baseband input signal; and
correcting at least one of the polynomial predistortion coefficient and the polynomial pre-equalization coefficient based on the comparison.
8. The method of claim 6 , further comprising:
downconverting the amplified signal to baseband;
monitoring out of band distortion of the baseband amplified signal; and
adjusting at least one of the polynomial predistortion coefficient and the polynomial pre-equalization coefficient based on the out of band distortion.
9. A system for reducing adjacent channel power ratio in a multi-channel wideband communication system, the system comprising:
a multiplier for combining a baseband input signal and a polynomial predistortion coefficient from plurality of polynomial predistortion coefficients, wherein the polynomial predistortion coefficient is based on an absolute value of the input signal multiplied by the number of predistortion coefficients in the plurality of predistortion coefficients, rounded to the nearest integer; and
an equalizer for pre-equalizing an output of the multiplier using one or more polynomial pre-equalization coefficients to compensate for memory effects in a power amplifier of the communication system.
10. The system of claim 9 , wherein the polynomial predistortion coefficient is calculated using the following equation:
F
m
(
u
(
n
-
k
)
)
=
∑
p
=
1
P
b
2
p
-
1
·
u
(
n
-
k
)
2
(
p
-
1
)
,
wherein 2p−1 is a polynomial order and b is a complex coefficient corresponding to the polynomial order.
11. The system of claim 10 , wherein pre-equalizing comprises using the following equation:
z
(
n
)
=
∑
k
=
0
K
-
1
∑
l
=
1
L
w
k
,
2
l
-
1
·
u
(
n
)
2
(
l
-
1
)
×
∑
p
=
1
P
b
2
p
-
1
·
u
(
n
-
k
)
·
u
(
n
-
k
)
2
(
p
-
1
)
,
wherein w k,l is a k-th tap and 1-th order coefficient.
12. The system of claim 9 , wherein the one or more polynomial pre-equalization coefficients correspond to filter coefficients of a finite impulse response filter.
13. The system of claim 9 , wherein the one or more polynomial pre-equalization coefficients correspond to filter coefficients of an infinite impulse response filter.
14. The system of claim 9 , further comprising:
an upconverter for upconverting an output of the equalizer to radio frequency; and
a downcoverter for downconverting an output of the power amplifier to baseband.
15. The system of claim 14 , further comprising:
a comparator for comparing an output of the downconverter to the baseband input signal.
16. The system of claim 14 , further comprising:
a bandpass filter and a power detector for monitoring out of band distortion of the output of the power amplifier.