Digital Predistortion Adaptation for Frequency and Gain Changes
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Solution Overview
Problem
The challenge in wireless device transmit chains is to effectively predistort transmit signals across a wide range of bandwidths and frequency ranges, particularly in 5G NR systems, where high peak-to-power ratio signals reduce power amplifier efficiency and introduce nonlinear effects, leading to dispersive channels and inefficiencies in both envelope tracking and average power tracking modes.
Innovation Solution
The implementation of a predistortion system that adapts predistortion functions to compensate for frequency and gain changes by determining frequency offsets and gain ratios, allowing the reuse of predistortion functions across different frequency ranges and gain states without additional calibration, using adaptation and inverse adaptation circuitry to correct for these changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple predistortion functions are used to cover different frequency ranges and gain states, then predistortion accuracy is improved, but device complexity and calibration requirements increase
Solution Approach 1:
The patent implements a universal predistortion function that can operate across multiple frequency ranges and gain states by incorporating frequency offset and gain ratio determination circuits. This single function adapts to different operating conditions through real-time parameter estimation, eliminating the need for multiple separate predistortion functions while maintaining accuracy.
Solution Approach 2:
The system dynamically adjusts operating parameters (frequency offset and gain ratio) based on current transmit chain conditions. By changing these parameters in real-time rather than using fixed predistortion functions, the system achieves adaptability across different frequency ranges and gain states without requiring multiple predetermined functions.
2Adaptability or versatility
If multiple predistortion functions are stored for different frequency ranges, then coverage of wide bandwidth is improved, but memory requirements and calibration time increase
Solution Approach 1:
The system performs preliminary determination of frequency offset and gain ratio parameters before applying predistortion. This preliminary action allows the single predistortion function to be properly configured for the current operating conditions, enabling wide frequency range coverage without requiring pre-stored functions for each frequency band.
Solution Approach 2:
The transmit chain automatically determines its own frequency offset and gain ratio parameters through built-in determination circuits. This self-service capability eliminates the need for external calibration procedures for each frequency range, reducing calibration time while maintaining broad frequency coverage.
3Productivity
If predistortion is performed without adaptation to frequency offsets, then processing speed is improved, but predistortion effectiveness decreases in dispersive channels
Solution Approach 1:
The system implements a feedback mechanism where frequency offset and gain ratio are continuously determined from the actual transmit chain operation and used to adjust the predistortion function in real-time. This feedback loop maintains predistortion effectiveness in dispersive channels without significantly impacting processing speed, as the parameter determination is integrated into the existing signal flow.
Data Source
AI summary
Systems, circuitries, and methods for predistorting a digital signal in a transmit chain based on a predistortion function are provided in which the function is determined based on a first digital signal or a first transmit chain state. A method includes: receiving a second digital signal that is input to the transmit chain, wherein the transmit chain is characterized by a present transmit chain state; performing a first operation on the second digital signal to generate an adapted digital signal, wherein the first operation is based on either a relationship between the first digital signal and the second digital signal, or a relationship between the first transmit chain state and the present transmit chain state; predistorting the adapted digital signal based on the predistortion function; and performing a second operation on the predistorted adapted signal, wherein the second operation corresponds to an inverse of the first operation.