Cube Coordinate Predistortion for Wideband PA Linearity
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Solution Overview
Problem
Existing power amplifier technologies face challenges in increasing linearity while maintaining power efficiency, particularly in wideband applications, where digital baseband predistortion techniques like look-up tables and polynomial signal processing are inefficient due to high computational complexity and poor performance.
Innovation Solution
A method that represents the power amplifier's response using multi-dimensional coefficient spaces, specifically Volterra Series, and employs cube coefficient subspaces (CCS) and diagonal cube coordinate subspaces (CCS-D) to efficiently search for and invert nonlinearities, reducing computational complexity and improving linearization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital baseband predistortion using standard polynomial signal processing is used, then linearity of power amplifier is improved, but computational complexity increases significantly
Solution Approach 1:
The patent segments the multi-dimensional signal space into multiple lower-dimensional subspaces (e.g., amplitude subspace, phase subspace, frequency subspace). Instead of using a single high-order polynomial across the entire signal space, the predistortion function is divided into multiple lower-order polynomial functions, each operating in a specific subspace. This segmentation reduces the computational complexity of evaluating the predistortion function while maintaining the ability to model complex nonlinear behaviors.
Solution Approach 2:
The patent transforms the problem from a high-dimensional polynomial evaluation into a multi-stage process operating in different dimensional subspaces. By decomposing the signal into components (amplitude, phase, frequency) and applying separate predistortion functions to each component, the method effectively reduces the dimensionality of each individual computation while collectively covering the full signal space.
2Manufacturing precision
If look-up table-based digital baseband predistortion is used, then linearity is improved, but performance decreases in wideband applications
Solution Approach 1:
The patent employs dynamic predistortion functions that adapt to the instantaneous characteristics of the input signal. Unlike static look-up tables that require exhaustive pre-computation and interpolation, the polynomial-based predistortion functions dynamically compute the correction based on current signal parameters (amplitude, phase, frequency). This dynamic approach allows the system to effectively handle wideband signals where signal characteristics vary rapidly across the bandwidth.
Solution Approach 2:
The patent changes the parameters of the predistortion function based on the input signal characteristics. The polynomial coefficients are selected or adjusted according to the current operating point (amplitude level, frequency offset, phase), allowing the system to maintain optimal linearity performance across different parts of the wideband signal spectrum.
3Manufacturing precision
If sufficiently deep memory and high polynomial order are used to span multi-dimensional signal space, then power amplifier nonlinear distortion is mitigated, but computational complexity increases
Solution Approach 1:
The patent segments the high-order polynomial evaluation into multiple lower-order polynomial evaluations operating in separate subspaces. Instead of computing a single high-order polynomial that requires deep memory and extensive computation, the method computes multiple lower-order polynomials in parallel or sequence, each operating on a specific signal component. This segmentation achieves equivalent nonlinear distortion mitigation with reduced computational burden.
Solution Approach 2:
The patent applies partial polynomial expansions in each subspace rather than attempting to model the entire multi-dimensional signal space with a single comprehensive high-order polynomial. By applying lower-order polynomials to specific signal components (amplitude, phase, frequency separately), the method achieves sufficient distortion mitigation without the excessive computational requirements of a full high-order expansion.
Data Source
AI summary
A method or corresponding apparatus relates to a mathematical approach to efficiently search for and localize regions in a multi-dimensional signal space to enable inversion of power amplifier nonlinearities with a significant reduction in computational complexity and an efficient hardware implementation. To linearize a wideband power amplifier, an example embodiment of the present invention may represent a response of the wideband power amplifier using coefficients in a cube coefficient subspace, and search over the full multi-dimensional subspace according to an optimization criterion in order to identify a vector of cube coefficient subspace coefficients. The vector of coefficient subspace coefficients may be used to linearize the wide-band power amplifier.