Adaptive Predistortion for RF Amplifiers with Burst Data
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Solution Overview
Problem
Predistortion systems in time-division duplex (TDD) air-interface face challenges with adaptive predistortion performing poorly due to amplifier nonlinearity variations during burst periods and power restrictions in mobile stations, leading to inefficient spectral and constellation error performance.
Innovation Solution
The implementation of three techniques: adaptation using a smaller subset of samples, selective application of digital predistortion under high power conditions, and adaptation of less than all predistortion coefficients, which can be applied independently or combined, to improve predistortion efficiency and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive predistortion is applied continuously over the entire burst period, then spectral performance is improved, but power consumption increases
Solution Approach 1:
The patent applies adaptive predistortion to only a subset of samples within the burst period rather than continuously processing all samples. This partial application maintains adequate spectral performance while significantly reducing the computational load and power consumption of the predistortion system.
Solution Approach 2:
The burst period is segmented into different regions, with adaptive predistortion applied selectively to specific segments (such as high-power regions) rather than uniformly across the entire burst. This segmentation allows the system to focus computational resources where they are most needed.
2Reliability
If digital predistortion is applied at all power levels, then linearization performance is improved, but power consumption increases
Solution Approach 1:
The patent applies digital predistortion selectively based on local conditions - specifically, only when the amplifier operates in high-power regions where nonlinearity is most problematic. Low-power regions are excluded from predistortion processing, optimizing the trade-off between linearization performance and power consumption.
Solution Approach 2:
The system dynamically changes the operational parameter of the predistortion function based on the input signal power level. A threshold mechanism is employed where predistortion is enabled only when the signal exceeds a certain power level, adapting the processing intensity to the actual nonlinear distortion risk.
3Measurement precision
If all predistortion coefficients are adapted continuously, then predistortion accuracy is improved, but computational complexity and power consumption increase
Solution Approach 1:
The patent extracts and processes only the most critical predistortion coefficients rather than adapting all coefficients continuously. By identifying and focusing on the subset of coefficients that have the greatest impact on predistortion accuracy, the system reduces computational complexity while maintaining adequate performance.
Solution Approach 2:
Instead of adapting all predistortion coefficients for every sample, the system applies coefficient adaptation partially - only to selected coefficients and only during specific conditions (such as high-power regions). This partial adaptation strategy reduces the overall computational burden while preserving essential predistortion functionality.
Data Source
AI summary
Apparatus and methods control predistortion of an RF transmitter. A base station or a mobile station can utilize predistortion to improve linearity characteristics of the RF power amplifier. When used effectively, predistortion limits spectral growth such that the amplified signal complies with regulatory requirements. With respect to bursty signals, specific improvement techniques are disclosed. A first technique is related to adaptation using only a smaller subset of samples of a burst. A second technique is related to selective application of digital predistortion, such as, only under high power conditions for a power amplifier. A third technique is directed to adaptation of less than all of the coefficients. These improvements permit the use of a smaller and less expensive amplifier for a given power class and can lengthen battery life for a mobile unit.