Method and system for baseband predistortion linearization in multi-channel wideband communication systems
An efficient baseband predistortion linearization method 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 comprising:
generating an address from samples of a baseband input signal, u(n-k), of a communication system, wherein k is a counter corresponding to a plurality of taps;
retrieving from a memoryless lookup table an entry, F m (|u(n)−k|), in accordance with the address for each tap of the plurality of taps;
multiplying the baseband input signal and the entry from the memoryless lookup table to generate a multiplied signal, x(n−k)=u(n−k)·F m (|u(n−k)|) for each tap of the plurality of taps;
pre-equalizing the multiplied signal by multiplying, for each tap of the plurality of taps, the multiplied signal, x(n−k), with an indexed coefficient corresponding to a magnitude of the baseband input signal, W k m (|u(n)|), to generate a pre-equalized signal for each tap of the plurality of taps;
summing the pre-equalized signal for each tap of the plurality of taps to generate an output signal, z(n)=Σ k=0 K W k m (|u(n)|)·x(n−k); and
outputting the output signal, z(n), to a power amplifier.
2. The method of claim 1 , wherein the multiplied signal is pre-equalized using a finite impulse response (FIR) filter.
3. The method of claim 1 , wherein the multiplied signal is pre-equalized using an infinite impulse response (IIR) filter.
4. The method of claim 1 , wherein the entry from the memoryless lookup table is a complex coefficient.
5. The method of claim 1 , wherein pre-equalizing the multiplied signal includes applying a piecewise equalization.
6. The method of claim 1 , further comprising:
updating the entry from the memoryless lookup table using an indirect learning method.
7. The method of claim 6 , wherein the indirect learning method uses a least mean square algorithm.
8. A system comprising:
an address generator configured to generate an address from samples of a baseband input signal, u(n−k), of a communication system, wherein k is a counter corresponding to a plurality of taps;
a memoryless lookup table configured to assign a coefficient, F m (|u(n)−k|), according to the address for each tap of the plurality of taps;
a multiplier configured to combine the baseband input signal and the coefficient to generate a multiplied signal, x(n−k)=u(n−k)·F m (|u(n−k)|) for each tap of the plurality of taps;
an equalizer configured to pre-equalize the multiplied signal by multiplying, for each tap of the plurality of taps, the multiplied signal, x(n−k), with an indexed coefficient corresponding to a magnitude of the baseband input signal, W k m (|u(n)|), to generate a pre-equalized signal for each tap of the plurality of taps;
a summer configured to sum the pre-equalized signal for each tap of the plurality of taps to generate an output signal, z(n)=Σ k=0 K W k m (|u(n)|)·x(n−k); and
a power amplifier configured to receive the output signal, z(n).
9. The system of claim 8 , wherein the equalizer comprises a finite impulse response (FIR) filter.
10. The system of claim 8 , wherein the equalizer comprises an infinite impulse response (IIR) filter.
11. The system of claim 8 , wherein the coefficient is a complex coefficient.
12. The system of claim 8 , wherein the equalizer is configured to apply a piecewise equalization.
13. The system of claim 8 , wherein the memoryless lookup table is further configured to update the coefficient using an indirect learning method.
14. The system of claim 8 , further comprising a digital-to-analog converter coupled to an output of the equalizer.
15. The system of claim 14 , further comprising an upconverter coupled to an output of the digital-to-analog converter.
16. The system of claim 15 , wherein the power amplifier is coupled to an output of the upconverter.
17. The system of claim 16 , further comprising a downconverter coupled to an output of the power amplifier and configured to convert the output of the power amplifier to a baseband output signal.
18. The system of claim 17 , further comprising:
a comparator configured to compare the baseband input signal to the baseband output signal to generate a comparison signal,
wherein the address generator is configured to update the address using the comparison signal and the memoryless lookup table is configured to update the coefficient using the comparison signal.