Digital Predistortion Adaptation Across Wide Frequency Offsets
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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, especially with the introduction of 5G NR, where higher bandwidths and complex modulation schemes lead to nonlinear effects and efficiency issues due to envelope tracking, making it difficult to maintain linearity and power amplifier efficiency.
Innovation Solution
The implementation of predistortion systems that adapt and reuse predistortion functions optimized for one frequency range or transmit chain state for different ranges and states, using adaptation circuitry to adjust for frequency offsets and gain changes, allowing for efficient compensation of nonlinear effects without additional calibration or learning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple predistortion functions are stored for different frequency ranges and transmit chain states, then predistortion effectiveness across wide bandwidths is improved, but device complexity and memory requirements increase
Solution Approach 1:
The patent implements a universal predistortion function that can operate across multiple frequency ranges and transmit chain states by incorporating frequency offset compensation and gain adjustment mechanisms. Instead of storing separate predistortion functions for each frequency range, the system uses a single base predistortion function that is dynamically adapted through frequency offset estimation and gain adjustment, allowing one function to serve multiple purposes across different operating conditions.
Solution Approach 2:
The system changes parameters (frequency offset and gain) of an existing predistortion function to adapt it for different frequency ranges and transmit chain states. By estimating the frequency offset between the calibration signal and the actual transmit signal, and adjusting the predistortion function accordingly through gain modification, the system can effectively handle different operating conditions without requiring separate stored functions for each scenario.
2Manufacturing precision
If predistortion functions are optimized for specific frequency ranges, then linearity is improved for those ranges, but performance deteriorates when operating outside the optimized range
Solution Approach 1:
The patent makes the predistortion function dynamic by incorporating frequency offset estimation and gain adjustment capabilities. The system continuously estimates the frequency offset between the calibration signal and the actual transmit signal, and dynamically adjusts the predistortion function's gain parameter accordingly. This dynamic adaptation allows the system to maintain optimal linearity performance across varying frequency ranges and transmit chain states, rather than being fixed to a single optimized range.
3Measurement precision
If calibration is performed for each frequency range and transmit chain state, then predistortion accuracy is improved, but calibration time and system complexity increase
Solution Approach 1:
The system performs preliminary calibration for a reference frequency range and transmit chain state, storing this base predistortion function for later use. During actual operation across different frequency ranges and states, the system estimates frequency offsets and adjusts the pre-calibrated function accordingly, avoiding the need to perform time-consuming calibration procedures for each individual frequency range and state combination.
Data Source
AI summary
Systems, circuitries, and methods for predistorting a digital signal in a transmit chain based on a predistortion function are provided. A method includes shifting a center frequency of an input signal by an offset to generate an adapted signal; predistorting the adapted signal based on a predistortion function to generate a predistorted adapted signal; reverting the shifting of the center frequency of the predistorted adapted signal by the offset to generate a predistorted signal; and causing transmission of the predistorted signal by a transmit chain.