Multiband digital predistortion for broadband communications
Techniques are described for implementing multiband digital predistortion in a broadband transmitter in a manner that provides effective compensation of non-linear distortion arising from integration of a high-power amplifier (HPA). Embodiments segment the signal spectrum of a transmit signal into multiple sub-band signals and apply non-linear distortion compensation separately and concurrently for each sub-band signal. The resulting multi-band digital predistortion (mDPD) compensates both for in-band distortion and for distortions from non-linear interactions between the frequency sub-bands. The disclosed mDPD can provide enhanced performance features, such as handling of memory effects, reduced sampling rate requirements for DPD components, and minimizing detrimental spectral regrowth at the HPA output.
1 . A transmitter comprising:
a segmenter configured to segment a wide-band (WB) input signal into N sub-band (SB) input signals, wherein N is an integer greater than 1;
a multi-band digital pre-distortion (mDPD) processor coupled with the segmenter, having a modular structure including modules, each corresponding to a respective sub-band combination, the mDPD processor configured to:
determine a subset of the modules as corresponding to respective sub-band combinations with significant contributions to non-linear distortion of the WB input signal; and
generate N pre-distorted SB signals from the N SB input signals by pre-compensating, in each module of only the subset of the modules, a respective SB input signal of the N SB input signals both for a respective estimated in-band distortion and for a respective estimated cross-band distortion corresponding to the sub-band combination associated with the module, wherein each respective estimated in-band distortion and each respective estimated cross-band distortion is derived from a model of non-linear characteristics of a high-power amplifier (HPA); and
a combiner coupled with the mDPD processor to generate a pre-distorted output signal based on combining the N pre-distorted SB signals.
2 . The transmitter of claim 1 , wherein each of the N pre-distorted SB signals is generated by combining contributions from those of the modules associated with sub-band combinations including the respective SB input signal.
3 . The transmitter of claim 1 , further comprising:
the HPA coupled with the combiner to generate an amplified output signal from the pre-distorted output signal.
4 . The transmitter of claim 3 , further comprising:
a feedback segmenter coupled between an output of the HPA and the mDPD processor to segment the amplified output signal into N SB feedback signals each in a sub-band corresponding to a respective one of the N pre-distorted SB signals,
wherein the mDPD processor is configured to update the model of non-linear characteristics of the HPA based on comparing the N SB feedback signals with the N pre-distorted SB signals.
5 . The transmitter of claim 1 , wherein the model of non-linear characteristics of the HPA accounts for memory effects of a designer-specified depth and nonlinearity of a designer-determined order.
6 . The transmitter of claim 1 , wherein the mDPD processor is configured to iteratively update pre-distortion coefficients based on new data captures.
7 . The transmitter of claim 1 , wherein the mDPD processor is configured to update the pre-distortion coefficients using a least squares solution.
8 . The transmitter of claim 1 , wherein the mDPD processor is configured to iteratively refine the pre-distortion coefficients using a damped Newton algorithm.
9 . The transmitter of claim 1 , wherein the mDPD processor models the non-linear characteristics of the HPA using a reduced-complexity Volterra model.
10 . The transmitter of claim 1 , wherein:
the N SB input signals are not time-aligned; and
the mDPD processor is configured to handle the non-time-aligned N SB input signals.
11 . A method comprising:
receiving a wide-band (WB) input signal;
segmenting the WB input signal into N sub-band (SB) input signals, wherein N is an integer greater than 1;
determining a subset of a plurality of sub-band combinations as having significant contributions to non-linear distortion of the WB input signal, wherein a multi-band digital pre-distortion (mDPD) processor has a modular structure including modules, each module corresponding to a respective one of the plurality of sub-band combinations, such that the subset of the plurality of sub-band combinations corresponds to a subset of the modules;
generating N pre-distorted SB signals from the N SB input signals by pre-compensating, in each module of only the subset of the modules, a respective SB input signal of the N SB input signals both for a respective estimated in-band distortion and for a respective estimated cross-band distortion corresponding to the sub-band combination associated with the module, wherein each respective estimated in-band distortion and each respective estimated cross-band distortion is derived from a model of non-linear characteristics of a high-power amplifier (HPA); and
combining the N pre-distorted SB signals to generate a pre-distorted output signal.
12 . The method of claim 11 , wherein each of the N pre-distorted SB signals is generated by combining contributions from those of the modules associated with sub-band combinations including the respective SB input signal.
13 . The method of claim 11 , further comprising:
generating an amplified uplink signal from the pre-distorted output signal using the HPA.
14 . The method of claim 13 , further comprising:
segmenting the amplified output signal into N SB feedback signals each in a sub-band corresponding to a respective one of the N pre-distorted SB signals; and
updating the model of non-linear characteristics of the HPA based on comparing the N SB feedback signals with the N pre-distorted SB signals.
15 . The method of claim 11 , wherein the model of non-linear characteristics of the HPA accounts for memory effects of a designer-specified depth and nonlinearity of a designer-determined order.
16 . The method of claim 11 , wherein the generating N pre-distorted SB signals from the N SB input signals comprises iteratively updating the pre-distortion coefficients based on new data captures.
17 . The method of claim 11 , wherein the generating N pre-distorted SB signals from the N SB input signals comprises updating the pre-distortion coefficients using a least squares solution.
18 . The method of claim 11 , wherein the generating N pre-distorted SB signals from the N SB input signals comprises iteratively refining the pre-distortion coefficients using a damped Newton algorithm.
19 . The method of claim 11 , further comprising:
modeling the non-linear characteristics of the HPA to generate the model using a reduced-complexity Volterra model.
20 . The method of claim 11 , wherein:
the N SB input signals are not time-aligned; and
the generating N pre-distorted SB signals from the N SB input signals comprises time-aligning the N SB input signals.