Adaptive Volterra Predistortion for Wideband Transmitter Linearization
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Solution Overview
Problem
Existing radio transmitter linearization techniques are limited in their ability to provide effective and economical minimization of transmission-related signal distortions across a wide range of input signals, particularly in contemporary wideband communication standards, and often require complex coordinate system transformations and sophisticated predistorter architectures.
Innovation Solution
An adaptive control system using inverse Volterra-series modeling with a look-up table-based implementation, which allows for higher order Volterra approximation terms with minimal complexity, utilizing dual-port RAMs and modular architecture to efficiently implement arbitrary order Volterra-series expansions, eliminating the need for power functions and polynomials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional coordinate system transformation methods are used for predistortion, then linearization can be achieved, but device complexity increases due to additional coordinate transformation requirements
Solution Approach 1:
The patent extracts only the magnitude information from the complex baseband signal, discarding the phase component. This extraction approach eliminates the need for complex coordinate system transformations while retaining sufficient information for effective predistortion, thereby reducing device complexity while maintaining linearization performance
Solution Approach 2:
Instead of transforming coordinates from one system to another as in traditional methods, the patent inverts the approach by directly using magnitude information in the original signal domain to generate the predistortion signal, avoiding coordinate transformation complexity entirely
2Reliability
If sophisticated predistorter architectures are used to achieve unconditionally convergent linearization, then linearization robustness improves, but device complexity increases
Solution Approach 1:
The patent uses only the magnitude component of the complex signal for predistortion, which is a partial action approach. This selective use of signal information achieves effective linearization without requiring the full complexity of sophisticated predistorter architectures, thereby reducing device complexity while maintaining robustness
Solution Approach 2:
The patent changes the parameter used for predistortion from the full complex signal (with both magnitude and phase) to only the magnitude parameter. This parameter change simplifies the predistorter architecture while maintaining linearization robustness by focusing on the most critical distortion-causing parameter
3Manufacturing precision
If higher order Volterra terms are included to improve linearization accuracy, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The patent segments the complex predistortion problem into separate magnitude and phase components, and further focuses only on the magnitude component. This segmentation allows higher order Volterra terms to be applied selectively to magnitude information, improving linearization accuracy while avoiding the exponential complexity increase that would result from applying them to the full complex signal
Data Source
AI summary
A linearizer for a non-linear transmitter includes a tap delay line that provides samples of an input signal at selected times. At least one Volterra tap is coupled to the tape delay line. The Volterra tap includes a lookup table representation of a polynomial. An adaptive controller is coupled to the Volterra tap for modifying values in the lookup table.