Digital Predistortion Initialization for Wideband High-Power Amplifiers
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Solution Overview
Problem
Existing digital predistortion (DPD) methods face challenges in determining filter coefficients for nonlinear high-power amplifiers (HPAs), especially in wideband applications with strong nonlinearities, leading to distortion and interference.
Innovation Solution
A multi-step method using a nonlinear filter with adaptive filter coefficients determined through an iterative process, employing multi-tone signals to reduce intermodulation distortions and compensate for nonlinearities across a wide range of frequencies and waveforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional DPD methods are used to determine filter coefficients, then the system is simpler to implement, but the method fails for strong nonlinearities and wideband applications
Solution Approach 1:
The patent implements a dynamic iterative adaptation process where filter coefficients are continuously updated based on measured intermodulation distortion levels. The system transitions from static coefficient determination to dynamic adaptation, allowing the DPD to effectively handle strong nonlinearities by adjusting coefficients in response to actual distortion measurements rather than relying on fixed theoretical models.
Solution Approach 2:
The patent introduces a feedback mechanism where the output signal is measured and used to update the filter coefficients in subsequent iterations. This closed-loop feedback allows the system to learn from actual distortion characteristics and improve compensation performance, making it robust to strong nonlinearities that cannot be predicted by open-loop methods.
2Ease of manufacture
If linear methods such as least-squares are used to solve for filter coefficients, then the computation is simpler, but the coefficients cannot be solved for because they are not linearly applied
Solution Approach 1:
The patent segments the coefficient determination process into multiple iterative steps. Each iteration focuses on reducing specific intermodulation distortion components by updating coefficients based on measured distortion levels. This segmentation allows the complex nonlinear problem to be solved through a series of simpler, more manageable adjustments while achieving high accuracy.
Solution Approach 2:
The patent replaces the traditional mechanical least-squares approach with an iterative adaptive system that uses measurement and feedback. Instead of relying on linear algebraic methods that assume linear coefficient application, the system uses iterative optimization that accounts for the nonlinear nature of HPA distortion, substituting computational mechanics with adaptive control.
3Adaptability or versatility
If DPD is applied to wideband applications with strong nonlinearities, then the coverage and effectiveness are improved, but the initialization of DPD is not robust and tends to fail
Solution Approach 1:
The patent employs periodic iteration cycles where the system alternates between applying DPD with current coefficients, measuring distortion levels, and updating coefficients. This periodic action allows the system to systematically address different distortion components across the wideband spectrum, building robust initialization through repeated measurement and adjustment cycles rather than attempting to solve all problems simultaneously.
Solution Approach 2:
The patent performs preliminary distortion measurements and coefficient adjustments before full operational use. By initially characterizing the HPA's nonlinear behavior through measured intermodulation products and pre-adjusting coefficients accordingly, the system establishes a robust starting point for wideband applications rather than beginning with unoptimized default values.
Data Source
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AI summary
An apparatus and method are provided for digital predistortion of an electrical signal to precompensate for nonlinear distortions in a nonlinear channel (e.g., a nonlinear channel including a high-power amplifier). The digital predistortion processor includes a nonlinear filter. Filter coefficients are determined using a modified input electrical signal having multiple simultaneous tones, using an iterative process which adapts the modified input electrical signal to reduce levels of intermodulation distortions in a modified output electrical signal.