Digital Multi-Channel Pre-Distortion for HPA Linearization
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Solution Overview
Problem
High power amplifiers (HPAs) used in communication systems introduce nonlinear distortion, especially when amplifying wideband signals, leading to signal clipping and phase shifts, which existing analog linearization methods struggle to accurately counteract, especially for multi-channel signals.
Innovation Solution
Implementing digital linearization by interpolating and frequency-shifting multiple digital baseband signals, combining them into a wideband signal, pre-distorting it to compensate for HPA distortions, and then decomposing it back into pre-distorted baseband signals for each channel, which are converted to analog and up-converted for input into the HPA, thereby reducing nonlinear distortion effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog pre-distortion methods are used to linearize HPA output, then the system complexity is lower, but the accuracy of distortion compensation deteriorates for multi-channel wideband signals
Solution Approach 1:
The patent replaces analog pre-distortion circuits with digital signal processing. Multiple digital baseband signals are interpolated, frequency-shifted, combined into a composite wideband signal, pre-distorted digitally, then decomposed and converted to analog for HPA input. This digital approach provides superior distortion compensation accuracy for multi-channel signals while managing complexity through software-based processing.
Solution Approach 2:
The patent segments the multi-channel signal processing into distinct digital stages: interpolation of individual channels, frequency shifting to respective channel frequencies, combination into composite signal, pre-distortion application, decomposition back to individual channels, and digital-to-analog conversion. This segmentation enables precise control and compensation of nonlinear distortions for each channel while maintaining overall system manageability.
2Reliability
If multiple digital baseband signals are combined into a composite wideband signal for pre-distortion, then the linearization accuracy is improved, but the processing complexity increases
Solution Approach 1:
The patent applies preliminary digital processing steps before pre-distortion: interpolating each digital baseband signal to increase sampling rate, frequency-shifting to respective channel frequencies, and combining into a composite wideband signal. This preliminary preparation ensures the composite signal is properly formatted for accurate pre-distortion compensation of HPA nonlinearities, improving overall linearization reliability.
Solution Approach 2:
The composite wideband digital signal serves as an intermediary representation that captures the combined characteristics of all channels. By pre-distorting this composite signal rather than individual channels separately, the system efficiently compensates for HPA nonlinearities affecting the combined signal, then decomposes it back to individual pre-distorted channel signals for output.
Data Source
AI summary
Digital baseband channel signals are received and up-sampled to a common sampling rate. The digital baseband channel signals are filtered using low pass filters. Complex frequency shifting is performed of the filtered digital baseband channel signals based on the associated different channel frequencies to obtain digital channel signals, which are combined to generate a digital wideband multi-channel signal that is a digital representation of an analog wideband multi-channel signal that is based on combining analog channel signals that correspond to the analog baseband channel signals. A non-linear pre-distortion of the digital wideband multi-channel signal is performed, the non-linear pre-distortion adding at least one of a gain and a phase shift to the digital wideband multi-channel signal such that the digital channel signals included within the digital wideband multi-channel signal are compensated for a non-linear distortion effected on the analog wideband multi-channel signal by a high-power amplifier.