Method and system of adaptive predistortion of a wireless transmitter
View Patent ↗A method of adaptive predistortion of a power amplifier, characterized in that the method comprises the steps of: storing values of a plurality of corresponding first and second coefficients; selecting one of the stored first coefficients; processing a first signal with the first coefficient to produce an input signal for the power amplifier; amplifying the input signal in the power amplifier to produce an output signal; calculating an error value from the output signal and a previously selected first coefficient; selecting a stored second coefficient corresponding with the previously selected first coefficient; updating the previously selected first coefficient with a value calculated from the error value and the second coefficient; updating the second coefficient; and replacing the previously selected first coefficient and corresponding second coefficient with the updated first and second coefficients respectively.
1. A method of adaptive predistortion of a power amplifier, characterised in that the method comprises the steps of:
storing values of a plurality of corresponding first and second coefficients;
selecting one of the stored first coefficients;
processing a first signal with the first coefficient to produce an input signal for the power amplifier;
amplifying the input signal in the power amplifier to produce an output signal;
calculating an error value from the output signal and a previously selected first coefficient;
selecting a stored second coefficient corresponding with the previously selected first coefficient;
updating the previously selected first coefficient with a value calculated from the error value and the second coefficient;
updating the second coefficient; and
replacing the previously selected first coefficient and corresponding second coefficient with the updated first and second coefficients respectively.
2. The method as claimed in claim 1 , wherein the step of updating the second coefficient comprises the step of progressively decreasing the value of the second coefficient.
3. The method as claimed in claim 2 , wherein the step of updating the second coefficient comprises the step of updating the second coefficient with a first order exponential decay term.
4. The method as claimed in claim 2 , wherein the step of updating the second coefficient comprises the step of updating the second coefficient with an expression modelled after the covariance matrix of the recursive least squares algorithm.
5. The method as claimed in claim 2 , wherein the step of updating the second coefficient comprises the step of resetting the updated second coefficient to a value substantially equal to zero in the event that the updated second coefficient is negatively valued.
6. The method as claimed in claim 2 , wherein the method further comprises the steps of resetting the method in the event that the error value exceeds a pre-defined threshold.
7. The method as claimed in claim 1 , wherein the step of updating the second coefficient comprises the step of updating the second coefficient with a first order exponential decay term.
8. The method as claimed in claim 7 , wherein the step of updating the second coefficient with a first order exponential decay term comprises the step of updating the second coefficient with a first order exponential decay term in the event that the sign of the error does not match that of the error calculated when that first coefficient was last selected.
9. The method as claimed in claim 8 , wherein the step of updating the second coefficient with a first order exponential decay term comprises the step of multiplying the second coefficient with a constant term of value between 0 and 1.
10. The method as claimed in claim 7 , wherein the step of updating the second coefficient with a first order exponential decay term comprises the step of multiplying the second coefficient with a constant term of value between 0 and 1.
11. The method as claimed in claim 7 , wherein the step of updating the second coefficient comprises the step of resetting the updated second coefficient to a value substantially equal to zero in the event that the updated second coefficient is negatively valued.
12. The method as claimed in claim 1 , wherein the step of updating the second coefficient comprises the step of updating the second coefficient with an expression modelled after the covariance matrix of the recursive least squares algorithm.
13. The method as claimed in claim 12 , wherein the step of updating the second coefficient comprises the step of decreasing the second coefficient with the expression
μ
{
x
(
n
-
D
)
}
2
x
(
n
-
D
)
2
1
+
x
(
n
-
D
)
2
μ
{
x
(
n
-
D
)
}
λ
,
wherein 0<=λ<=1, and wherein n is a time instant, D is a delay time, x(n−D) is the first signal at delayed time instant n−D, and μ{|x(n−D)|} is an adaptation factor depending on an absolute value of x(n−D).
14. The method as claimed in claim 12 , wherein the step of updating the second coefficient comprises the step of resetting the updated second coefficient to a value substantially equal to zero in the event that the updated second coefficient is negatively valued.
15. The method as claimed in claim 1 , wherein the step of updating the second coefficient comprises the step of resetting the updated second coefficient to a value substantially equal to zero in the event that the updated second coefficient is negatively valued.
16. The method as claimed in claim 1 , wherein the method further comprises the steps of resetting the method in the event that the error value exceeds a pre-defined threshold.
17. The method as claimed in claim 1 , wherein the method comprises the step of terminating the method in the event that a second coefficient has a value below a pre-defined lower threshold.
18. A power amplifier apparatus comprising:
a power amplifier;
an adaptive predistorter;
at least two look-up tables comprising substantially the same number of elements;
a seeding means adapted to provide and store a plurality of first coefficients in the first look-up table and a plurality of corresponding second coefficients in the second look-up table;
a first selection means adapted to select one of the first coefficients from the first look-up table;
a processing means adapted to process a first signal with the selected first coefficient to produce an input signal for the power amplifier;
an error calculating means adapted to calculate an error value from an output signal from the power amplifier and a previously selected first coefficient;
a second selection means adapted to select a stored second coefficient corresponding with the previously selected first coefficient;
a first adaptation engine adapted to update the previously selected first coefficient with a value calculated from the error value and the second coefficient;
a second adaptation engine adapted to update the second coefficient; and
a data writing means adapted to replace the previously selected first coefficient in the first look-up table with the updated first coefficient; and to replace the corresponding second coefficient in the second look-up table with the updated second coefficient.
19. A wireless transmitter comprising the apparatus as claimed in claim 18 .
20. A wireless handset comprising the apparatus as claimed in claim 18 .