Baseband Predistortion Using Piecewise LUT Pre-Equalization
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Solution Overview
Problem
Existing baseband predistortion methods struggle to effectively compensate for both RF frequency response memory effects and bias-induced or thermal memory effects in multi-channel wideband wireless transmitters, leading to limitations in linearity and efficiency due to high computational complexity and numerical instability.
Innovation Solution
A piecewise pre-equalized lookup table (LUT) based predistortion system is employed, which reduces computational complexity and numerical instability while compensating for electrical and thermal memory effects, using a LUT with pre-equalized coefficients to address nonlinearities and memory effects in power amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If memory polynomial PD is used to compensate memory effects, then linearity performance is improved, but computational complexity increases significantly
Solution Approach 1:
The predistorter is segmented into multiple parallel memoryless predistorter branches, each handling a specific frequency band or signal component. This segmentation allows the complex memory compensation task to be divided into simpler parallel operations, reducing overall computational complexity while maintaining linearity performance.
Solution Approach 2:
An intermediary processing stage is introduced between the input signal and the memoryless predistorters, which pre-processes the signal to extract features or transform it into a form that enables more efficient predistortion computation. This intermediary step reduces the computational burden on subsequent stages.
2Measurement precision
If higher order polynomial terms are included in memory polynomial PD, then compensation accuracy is improved, but numerical instability increases due to matrix inversion
Solution Approach 1:
Instead of using expensive and numerically unstable high-order memory polynomial models requiring matrix inversion, the patent employs simpler memoryless predistorter models in parallel configurations. These simpler models achieve comparable compensation accuracy without the numerical instability associated with high-order polynomial matrix operations.
Solution Approach 2:
The patent inverts the traditional approach by not directly modeling the complex memory effects through high-order polynomials, but rather by using multiple simpler memoryless models in parallel that collectively achieve the same compensation effect, thereby avoiding the numerical inversion problem.
3Use of energy by moving object
If RF power amplifier operates in compression region to improve efficiency, then power efficiency increases, but linearity deteriorates due to nonlinearities
Solution Approach 1:
The predistorter applies preliminary correction to the input signal before it reaches the power amplifier. By pre-compensating for the expected nonlinear distortion in the compression region, the overall system achieves both high efficiency (amplifier operating in compression) and good linearity (distortion pre-corrected).
Solution Approach 2:
The predistorter generates a preliminary anti-distortion signal that counteracts the nonlinear effects of the power amplifier operating in compression. This preliminary anti-action ensures that when the distorted signal passes through the amplifier, the net result is linear output with high efficiency.
Data Source
AI summary
An efficient baseband predistortion linearization method for reducing the spectral regrowth and compensating memory effects in wideband communication systems using effective multiplexing modulation technique such as wideband code division multiple access and orthogonal frequency division multiplexing is disclosed. The present invention is based on the method of piecewise pre-equalized lookup table based predistortion, which is a cascade of a lookup table predistortion and piecewise pre-equalizers, to reduce the computational complexity and numerical instability for desired linearity performance with memory effects compensation for wideband transmitter systems.