Baseband Predistortion Using Piecewise LUTs for PA Memory Effects
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Solution Overview
Problem
Existing digital predistortion techniques struggle to effectively compensate for memory effects in RF power amplifiers, particularly in wideband applications, due to their complexity and inability to address thermal and bias-induced memory effects, leading to limited performance in multi-channel wireless transmitters.
Innovation Solution
A piecewise pre-equalized lookup table (LUT) based predistortion system is introduced, which reduces computational complexity and numerical instability by using a pre-equalized LUT to compensate for electrical and thermal memory effects, while maintaining linearity performance comparable to memory polynomial PDs.
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
Solution Approach 1:
The predistortion function is segmented into multiple lookup tables (LUTs) organized in a tree structure, where each node contains a LUT. This segmentation divides the complex memory polynomial computation into smaller, manageable table lookups, reducing computational complexity while maintaining linearity performance through piecewise pre-equalization.
Solution Approach 2:
The lookup tables are pre-computed and stored in memory during an offline training phase. This preliminary action transfers the computational burden from real-time operation to the offline setup phase, allowing the system to achieve memory polynomial-like performance with significantly reduced real-time computational complexity.
2Reliability
If Volterra filter structure is used to compensate memory effects, then memory effects are addressed, but device complexity becomes extremely high
Solution Approach 1:
The invention replaces the complex Volterra filter structure with simpler lookup tables that can be stored in memory. Instead of performing heavy real-time computations with Volterra filters, the system uses pre-computed LUTs that provide equivalent memory effects compensation with much lower device complexity and computational requirements.
3Object-generated harmful factors
If digital predistortion is applied to enhance linearity, then spectral regrowth is reduced, but computational load increases
Solution Approach 1:
The invention creates a digital copy of the power amplifier's nonlinear behavior through lookup tables that model the AM-AM and AM-PM characteristics. This digital model (copy) is used to pre-distort the signal, canceling out the expected nonlinearities before they occur, thereby reducing spectral regrowth with minimal real-time computational load.
Data Source
AI summary
An efficient baseband predistortion linearization method 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.