Factored Volterra Compensation for RF Nonlinear Distortion
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Solution Overview
Problem
Conventional linearization techniques for power amplifiers and analog-to-digital converters are limited in their ability to correct nonlinear distortion, especially in advanced RF systems with high instantaneous bandwidths, and require excessive signal processing resources, making them inefficient and costly.
Innovation Solution
The implementation of factored Volterra compensators, including multi-rate and oversampled Volterra compensators, which use higher-order Volterra kernels and adaptive processing algorithms to accurately model and correct nonlinear distortion across varying operating conditions, reducing computational complexity and resource requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional linearization techniques are used to correct nonlinear distortion, then some linearity improvement is achieved, but the correction range is limited and signal processing resources are excessively consumed
Solution Approach 1:
The patent segments the complex nonlinear distortion correction problem into multiple manageable components: (1) distortion detection module that identifies nonlinear distortion characteristics, (2) correction signal generation module that creates compensation signals, and (3) signal combination module that merges correction signals with original signals. This segmentation enables accurate linearity correction while reducing overall system complexity by handling each aspect separately with dedicated optimized modules
Solution Approach 2:
The patent applies preliminary action by pre-calculating and storing correction signals in lookup tables before actual signal processing occurs. The system pre-characterizes the nonlinear distortion behavior of power amplifiers and ADCs under various operating conditions, storing the inverse distortion characteristics in advance. During operation, the system simply retrieves pre-computed correction signals from memory rather than performing complex real-time calculations, significantly reducing signal processing resource requirements while maintaining high correction accuracy
2Measurement precision
If higher-order Volterra kernels are used to model nonlinear distortion, then correction accuracy improves, but computational complexity increases
Solution Approach 1:
The patent applies partial action by selectively implementing only the necessary higher-order Volterra kernel computations rather than calculating all possible kernel orders. The system dynamically determines which kernel orders are needed based on the specific distortion characteristics detected in the signal, computing only those kernels that provide meaningful correction. This approach achieves high modeling accuracy for the dominant distortion components while avoiding the excessive computational burden of calculating all higher-order kernels, thus resolving the contradiction between accuracy and complexity
3Use of energy by moving object
If power amplifiers operate at higher efficiency configurations, then energy efficiency improves, but linearity deteriorates due to increased nonlinearity
Solution Approach 1:
The patent converts the harmful nonlinearity generated by high-efficiency power amplifier operation into a beneficial correction signal. The system detects the specific nonlinear distortion patterns produced by the power amplifier operating in high-efficiency modes, generates inverse distortion signals that match these patterns, and combines them with the original signal. This approach allows the power amplifier to operate at high efficiency while the introduced nonlinearity is systematically canceled out, transforming what was previously a detrimental effect into a manageable and correctable characteristic
Solution Approach 2:
The patent implements feedback mechanisms where the output signal from the power amplifier is monitored, analyzed for nonlinear distortion characteristics, and used to generate appropriate correction signals. The system continuously measures the actual distortion behavior of the power amplifier under varying operating conditions and dynamically adjusts the correction signals accordingly. This closed-loop feedback approach enables the system to maintain high linearity accuracy even as the power amplifier operates in high-efficiency nonlinear regions, effectively decoupling efficiency performance from linearity performance
4Ease of manufacture
If traditional pre-distortion techniques with second-order or third-order polynomials are used, then implementation is simple, but accuracy is insufficient for high instantaneous bandwidth systems
Solution Approach 1:
The patent applies dynamics by transitioning from static polynomial coefficients to dynamic, adaptive correction parameters. The system continuously monitors operating conditions including temperature, input signal characteristics, and power amplifier state, and dynamically adjusts the Volterra kernel parameters and correction signals in real-time. This dynamic adaptation enables the system to maintain high correction accuracy across varying operating conditions and for high instantaneous bandwidth signals, whereas traditional fixed polynomial approaches fail to adapt to changing conditions
Data Source
AI summary
The present invention is a computationally-efficient compensator for removing nonlinear distortion. The compensator operates in a digital post-compensation configuration for linearization of devices or systems such as analog-to-digital converters and RF receiver electronics. The compensator also operates in a digital pre-compensation configuration for linearization of devices or systems such as digital-to-analog converters, RF power amplifiers, and RF transmitter electronics. The compensator effectively removes nonlinear distortion in these systems in a computationally efficient hardware or software implementation by using one or more factored multi-rate Volterra filters. Volterra filters are efficiently factored into parallel FIR filters and only the filters with energy above a prescribed threshold are actually implemented, which significantly reduces the complexity while still providing accurate results. For extremely wideband applications, the multi-rate Volterra filters are implemented in a demultiplexed polyphase configuration which performs the filtering in parallel at a significantly reduced data rate. The compensator is calibrated with an algorithm that iteratively subtracts an error signal to converge to an effective compensation signal. The algorithm is repeated for a multiplicity of calibration signals, and the results are used with harmonic probing to accurately estimate the Volterra filter kernels. The compensator improves linearization processing performance while significantly reducing the computational complexity compared to a traditional nonlinear compensator.