Subsampled Linearization for Power Amplifier Digital Predistortion
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Solution Overview
Problem
Existing digital predistortion systems face challenges in determining accurate digital predistorter coefficients due to the bandwidth mismatch between the transmit chain and the observation receiver, which limits their ability to capture non-linear effects outside the desired transmit bandwidth.
Innovation Solution
A method that involves calibrating digital predistorter coefficients by sweeping the receiver LO frequency in steps to cover the full transmit bandwidth, using regularization coefficients for robustness, and storing these coefficients in a database for later inference and application during runtime, even with partial information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the observation receiver bandwidth is reduced to match the input signal bandwidth, then the receiver complexity and power consumption are reduced, but the ability to capture non-linear effects outside the desired transmit bandwidth is lost
Solution Approach 1:
The system performs preliminary calibration by sweeping the receiver LO frequency across the full transmit bandwidth to capture complete non-linear effects. This pre-captured data is stored and later used to inform DPD coefficient selection, allowing the receiver to operate with limited bandwidth during normal transmission while maintaining accurate linearization capability.
Solution Approach 2:
The system transitions from a single-dimensional bandwidth constraint to a multi-dimensional solution space by introducing time-domain calibration phases. During these phases, the receiver temporarily expands its effective measurement bandwidth through LO frequency sweeping, capturing non-linear effects that are then processed to create a comprehensive model for DPD operation during normal transmission.
2Measurement precision
If the receiver LO frequency is swept across the full transmit bandwidth during calibration, then complete channel information is obtained for accurate DPD design, but the calibration time and power consumption increase
Solution Approach 1:
The calibration process is segmented into discrete LO frequency steps that sweep across the transmit bandwidth. At each step, the system captures specific frequency segments of the output signal. This segmented approach allows systematic collection of complete channel information while enabling efficient processing and storage of calibration data for later DPD coefficient determination.
3Measurement precision
If digital predistorter coefficients are determined for the entire transmit bandwidth, then linearization accuracy across the full bandwidth is improved, but the computational complexity and data storage requirements increase
Solution Approach 1:
Instead of using a single uniform DPD coefficient set for the entire bandwidth, the system determines multiple coefficient sets, each optimized for specific frequency segments or operating conditions. The appropriate coefficient set is selected based on the current operating point, allowing high linearization accuracy across the full bandwidth while managing complexity through localized optimization.
Solution Approach 2:
The system dynamically selects DPD coefficients from a pre-computed database based on real-time operating conditions inferred from subsampled output measurements. This dynamic adaptation allows the DPD to maintain optimal linearization performance across varying operating points without requiring complex real-time computation of coefficient sets.
Data Source
AI summary
Disclosed are implementations that include a method comprising applying at least one input signal to a power amplification system, that includes a transmit chain with a power amplifier (PA) producing output with non-linear distortions, to produce at least one output signal, and measuring at least one observed signal of the output signal using an observation receiver coupled to an output of the transmit chain, the observation receiver having a receive bandwidth smaller than a transmit chain bandwidth of the transmit chain. Measuring the at least one observed signal includes measuring multiple frequency segments of output signal. The method further includes determining one or more sets of digital predistortion coefficients based on the measured multiple frequency segments of the at least one output signal, with each of the sets of digital predistortion coefficients being associated with a respective set of operating conditions of the power amplification system.