Power Amplifier Predistortion Lookup Table for Memory Effects
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Solution Overview
Problem
Existing predistortion schemes for power amplifiers face challenges in efficiently compensating for nonlinear distortion, particularly the memory effect, which affects wideband frequency signals, leading to increased complexity and reduced convergence speed due to high computational requirements and large logic circuits.
Innovation Solution
A predistortion apparatus and method that calculates polynomial coefficients to determine predistortion gains for a look-up table, allowing for efficient compensation of nonlinear distortion in power amplifiers using a Finite Impulse Response (FIR) structure, which processes previous input signals to generate predistorted outputs suitable for wideband base stations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a polynomial predistorter is used to compensate for power amplifier nonlinearity, then convergence speed is improved, but device complexity increases due to many calculations and large logic circuits
Solution Approach 1:
The patent creates a simplified copy of the polynomial predistorter by converting it into a lookup table structure. Instead of implementing the full polynomial calculation logic, the system pre-calculates predistortion values and stores them in a lookup table, copying only the essential functional behavior while eliminating complex computational circuits.
Solution Approach 2:
The patent performs preliminary calculation of predistortion values offline and stores them in a lookup table before actual operation. During runtime, the system only needs to perform table lookup and interpolation operations rather than complex polynomial calculations, significantly reducing real-time computational complexity while maintaining convergence performance.
2Measurement precision
If the number of previous input samples is increased to compensate for memory effect, then compensation accuracy is improved, but computational complexity increases exponentially
Solution Approach 1:
The patent segments the predistortion function into multiple independent lookup tables, each handling a specific aspect of the memory effect. By dividing the complex compensation task into separate tables that can be independently accessed and updated, the system achieves high compensation accuracy without requiring exponential computational resources.
Solution Approach 2:
The patent uses lookup tables to store pre-computed predistortion values that account for multiple previous input samples. This copying approach replaces the need for real-time exponential calculations with simple table lookups, maintaining high compensation accuracy while dramatically reducing computational complexity.
3Object-generated harmful factors
If a feed-forward scheme is used to remove spurious components, then spurious signal removal is improved, but amplification efficiency decreases and system size increases
Solution Approach 1:
The patent replaces the analog feed-forward cancellation mechanism with a digital predistortion approach. Instead of using additional RF amplifiers and signal paths to cancel spurious components, the system uses digital signal processing to pre-distort the input signal, eliminating spurious components before they are generated by the power amplifier. This substitution maintains high amplification efficiency while achieving effective spurious signal removal.
Data Source
AI summary
A polynomial predistortion apparatus and method for compensating for a nonlinear distortion characteristic of a power amplifier is provided. The apparatus and method comprise an adaptation controller for determining polynomial coefficients by calculating an inverse nonlinear distortion characteristic of the power amplifier, and calculating complex predistortion gains for all possible amplitudes of an input signal using the determined polynomial coefficients; and a predistorter for receiving an input signal which is a combination of complex-modulated previous baseband input signal samples and current input signal samples, predistorting the input signal using the complex predistortion gains output from the adaptation controller, and outputting the predistorted input signal to the power amplifier.