Wide bandwidth digital predistortion system with reduced sampling rate
A digital predistortion linearization method is provided for increasing the instantaneous or operational bandwidth for RF power amplifiers employed in wideband communication systems. Embodiments of the present invention provide a method of increasing DPD linearization bandwidth using a feedback filter integrated into existing digital platforms for multi-channel wideband wireless transmitters. An embodiment of the present invention utilizes a DPD feedback signal in conjunction with a low power band-pass filter in the DPD feedback path.
1. A method of operating a communications system, the method comprising:
receiving a signal at a digital predistorter (DPD) having a DPD bandwidth;
introducing predistortion to the signal using the DPD to generate a predistorted signal;
filtering the predistorted signal using a digital filter to generate a filtered signal, wherein the predistorted signal is filtered over a filter bandwidth less than the DPD bandwidth;
amplifying the filtered signal to generate an amplified signal;
coupling a first portion of the amplified signal to provide a feedback signal; and
filtering the feedback signal using a band-pass filter to generate a filtered feedback signal, wherein the band-pass filter has a filter bandwidth less than the DPD bandwidth.
2. The method of claim 1 , wherein introducing predistortion to the signal using the DPD comprises applying an indirect learning algorithm.
3. The method of claim 2 , wherein applying an indirect learning algorithm comprising using a coefficient estimator.
4. The method of claim 1 , wherein introducing predistortion to the signal using the DPD comprises applying a coefficient estimator.
5. The method of claim 1 , wherein the signal comprises digital complex input samples.
6. The method of claim 1 , further comprising:
converting the filtered signal to an analog signal; and
modulating the analog signal to generate a modulated signal.
7. The method of claim 6 , wherein the analog signal is modulated using an analog quadrature modulator (AQM).
8. The method of claim 6 , further comprising:
downconverting the filtered feedback signal to generate a downconverted signal;
converting the downconverted signal to a digital signal; and
providing the digital signal to the DPD.
9. The method of claim 8 , wherein downconverting the filtered feedback signal includes:
mixing the filtered feedback signal with a local oscillator signal.
10. The method of claim 8 , further comprising:
filtering a second portion of the amplified signal with a duplexer to generate an output signal; and
transmitting the output signal.
11. A communications system comprising:
a digital predistorter (DPD) operable to receive an input signal and output a predistorted input signal, wherein the DPD is characterized by a first bandwidth;
a digital filter operable to receive the predistorted input signal and output a filtered input signal, wherein the digital filter is characterized by a second bandwidth that is less than the first bandwidth;
a power amplifier operable to amplify the filtered input signal and output an amplified signal; and
a band-pass filter operable to receive a portion of the amplified signal in a feedback path, wherein the band-pass filter is characterized by a third bandwidth that is less than the first bandwidth, and wherein the band-pass filter is operable to output a filtered feedback signal.
12. The communications system of claim 11 , wherein the DPD is operable to apply an indirect learning algorithm.
13. The communications system of claim 11 , wherein the DPD comprises a coefficient estimator.
14. The communications system of claim 13 , wherein the DPD is operable to apply an indirect learning algorithm.
15. The communications system of claim 11 , wherein the input signal comprises digital complex input samples.
16. The communications system of claim 11 , further comprising:
a digital-to-analog converter operable to convert the filtered input signal to an analog signal; and
a modulator operable to modulate the analog signal to generate a modulated signal.
17. The communications system of claim 16 , wherein the modulator is an analog quadrature modulator (AQM).
18. The communications system of claim 16 , further comprising:
a downconverter operable to downconvert the filtered feedback signal to generate a downconverted signal; and
an analog-to-digital converter operable to convert the downconverted signal to a digital signal and coupled to the DPD.
19. The communications system of claim 18 , wherein the downconverter includes:
a mixer operable to mix the filtered feedback signal with a local oscillator signal.
20. The communications system of claim 18 , further comprising:
a duplexer operable to filter a second portion of the amplified signal to generate an output signal; and
an antenna operable to transmit the output signal.