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 an input signal at a digital predistorter (DPD) having a DPD bandwidth;
introducing predistortion to the input signal using the DPD to generate a predistorted input signal;
filtering the predistorted input signal using a digital filter to generate a filtered input signal, wherein the predistorted input signal is filtered over a filter bandwidth less than the DPD bandwidth;
amplifying the filtered input signal to generate an amplified signal; and
filtering at least a portion of the amplified 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 input 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 input signal using the DPD comprises applying a coefficient estimator.
5. The method of claim 1 , wherein the input signal comprises digital complex input samples.
6. The method of claim 1 , further comprising:
converting the filtered input signal to an analog signal; and
modulating the analog signal to generate a modulated signal.
7. The method of claim 6 , wherein modulating the analog signal comprises 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. The method of claim 1 , wherein the band-pass filter comprises a radio frequency (RF) band-pass filter.
12. The method of claim 1 , wherein the band-pass filter comprises an intermediate frequency (IF) band-pass filter.