Multirate Memory Polynomial Pre-Distortion for Saturated Power Amplifiers
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Solution Overview
Problem
High power amplifiers in satellite communications systems cause significant non-linear and memory effect distortions, leading to reduced throughput and performance, which existing pre-distortion techniques, such as symbol and sample pre-distortion, are unable to fully address effectively.
Innovation Solution
A multi-rate, iterative memory polynomial model is employed for pre-distorting digital signals before amplification to correct for these distortions, using a pre-distorter that models the high power amplifier and associated components, optimizing pre-distorter taps through iterative and gradient-based methods to minimize error vector magnitude (EVM).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high power amplifiers operate at or near saturation level to provide high throughput and increased efficiency, then power efficiency and throughput are improved, but non-linear distortions and memory effect distortions increase significantly
Solution Approach 1:
The patent applies pre-distortion processing before the signal enters the power amplifier. A pre-distorter modifies the input signal in advance to compensate for the expected non-linear distortions and memory effects that will occur during amplification. This preliminary action counteracts the harmful distortions before they are generated, allowing the amplifier to operate at saturation without degrading signal quality.
Solution Approach 2:
The patent employs an iterative adaptive algorithm that uses feedback from the actual amplifier output to continuously optimize the pre-distorter coefficients. The system measures the actual distortions produced by the amplifier and adjusts the pre-distortion parameters accordingly, creating a closed-loop control system that maintains optimal performance despite variations in amplifier characteristics.
2Use of energy by moving object
If high power amplifiers operate at or near saturation level to maximize power output, then power efficiency is improved, but memory effect distortions increase
Solution Approach 1:
The pre-distorter is configured to anticipate and compensate for memory effects by incorporating past signal samples into the distortion compensation calculation. The memory polynomial model uses historical signal information to predict and counteract the memory-dependent non-linearities that occur when the amplifier operates at high efficiency points.
Solution Approach 2:
The patent models the amplifier's memory effects by introducing memory-dependent parameters into the polynomial expansion. The memory polynomial model includes terms that account for the amplifier's state at previous time instances, allowing the pre-distorter to adapt its compensation strategy based on the dynamic operating conditions and maintain low distortion across varying power efficiency levels.
3Reliability
If existing pre-distortion techniques (symbol or sample pre-distortion) are used to correct distortions, then some distortion reduction is achieved, but performance and throughput are still limited
Solution Approach 1:
The patent transitions from traditional symbol-rate or low-rate sample pre-distortion to a multi-rate pre-distortion approach that operates at multiple sampling rates simultaneously. By processing signals at higher rates and incorporating memory effects across different time scales, the system achieves more comprehensive distortion correction while maintaining higher throughput capabilities through efficient multi-rate signal processing.
Solution Approach 2:
The patent implements a dynamic pre-distorter that adapts its processing rate and complexity based on the operating conditions. The iterative adaptive algorithm continuously updates the pre-distortion parameters in real-time, allowing the system to optimize the balance between distortion correction accuracy and processing throughput, thereby improving both reliability and productivity simultaneously.
Data Source
AI summary
A system and method for pre-distorting a digital signal in a digital communications system. The method includes converting digital bits to be transmitted to a series of symbols defining the bits and providing the symbols to a pulse shaping filter (PSF) that provides samples of the symbols at a predetermined sample rate. The method also includes providing the filtered samples to a pre-distorter that pre-distorts the samples, wherein pre-distorting the samples includes providing a non-linear transformation of the samples that is defined by pre-distorter taps, and providing the pre-distorted samples to a power amplifier to be transmitted, where pre-distorting the samples includes modeling the power amplifier and associated transmitter components using a degree three memory polynomial.