Adaptive Cartesian Predistortion for Transmitter Linearization
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Solution Overview
Problem
Existing wireless transmitters, particularly those in cellular communication systems like WCDMA, face challenges in achieving linearization due to amplifier nonlinearities, which are not adequately addressed by factory-calibrated predistortion lookup tables under varying operational conditions such as temperature, voltage, and frequency changes.
Innovation Solution
A method and apparatus for adaptive Cartesian transmitter linearization using a predistorter with compensation lookup tables that are updated based on real-time feedback from a receiver, employing iterative adaptation algorithms to minimize distortion and adapt to changing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If factory-calibrated predistortion lookup tables are used, then initial linearization is achieved, but adequate linearization under varying operational conditions (temperature, voltage, frequency) cannot be maintained
Solution Approach 1:
The patent implements a feedback mechanism where the receiver measures the transmitted signal and feeds back information about signal quality metrics (such as error vector magnitude) to the predistorter. This feedback loop enables the system to detect deviations from optimal linearization performance and trigger updates to the lookup tables, thereby maintaining reliable linearization under varying operational conditions.
Solution Approach 2:
The patent transitions from static factory-calibrated lookup tables to dynamic, adaptively updated lookup tables. The system continuously monitors performance and updates the predistortion parameters in real-time based on current operational conditions, making the linearization system dynamic rather than static, thus maintaining effectiveness across temperature, voltage, and frequency variations.
2Reliability
If adaptive predistortion with real-time LUT updates is implemented, then linearization performance under varying conditions is maintained, but device complexity and computational requirements increase
Solution Approach 1:
The patent implements selective updating of lookup table entries rather than complete re-calibration. The system updates only those LUT entries that have become inaccurate due to operational condition changes, based on feedback from the receiver. This partial action approach maintains linearization performance while reducing the computational burden and complexity compared to full re-calibration.
Solution Approach 2:
The patent performs preliminary factory calibration to establish initial lookup tables that provide adequate linearization under nominal conditions. This preliminary action reduces the burden on the adaptive system, which only needs to make incremental adjustments from this pre-established baseline rather than starting from scratch, thereby reducing overall system complexity.
3Reliability
If factory calibration is performed, then initial predistortion parameters are established, but aging and environmental changes cause predistortion inadequacy over time
Solution Approach 1:
The patent implements continuous monitoring and periodic updating of predistortion parameters through the feedback loop. The receiver continuously measures signal quality and triggers LUT updates when degradation is detected, ensuring that the useful action of linearization continues effectively over the entire operational lifetime of the transmitter, counteracting the effects of aging and environmental changes.
Solution Approach 2:
The system performs self-adjustment by using its own transmitted signal as the test signal and using the receiver feedback to automatically update its predistortion parameters. This self-service capability eliminates the need for external re-calibration equipment or manual intervention, allowing the system to maintain adequate linearization performance throughout its operational life by autonomously adapting to aging and environmental changes.
Data Source
AI summary
A Cartesian transmitter and a method of linearizing a Cartesian transmitter. In one embodiment, the transmitter includes: (1) a transmit chain configured to receive an input signal having in-phase and quadrature components and having a predistorter configured to employ at least one compensation lookup table to carry out in-phase and quadrature compensation predistortion with respect to the input signal, a combiner configured to combine outputs of the predistorter and a nonlinear element configured to process an output of the combiner, (2) a receiver coupled to the transmit chain and (3) predistortion compensation circuitry associated with the receiver and configured to update the at least one compensation lookup table based on the input signal and a signal from the receiver.