RF Power Amplifier Nonlinear Model for Dynamic Predistortion
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Solution Overview
Problem
Modern communication systems face challenges in reducing power loss and distortion in radiofrequency power amplifiers used in mobile radio base stations, particularly due to the nonlinear transfer response of these components, which leads to spectral broadening and interference with adjacent channels.
Innovation Solution
A method is developed to accurately determine a model of the radiofrequency power amplifier's nonlinear dynamic transfer response with a system that accounts for memory effects, allowing for dynamic and flexible calculation of predistortion coefficients, enabling operation in a nonlinear range while minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the radiofrequency power amplifier is operated in a nonlinear range to improve efficiency and reduce costs, then power efficiency is improved, but signal distortion and spectral broadening increase
Solution Approach 1:
The patent applies digital predistortion by pre-processing the input signal before it enters the power amplifier. A predistorter circuit generates a distorted version of the input signal that compensates for the expected nonlinearities of the amplifier. This preliminary action allows the amplifier to operate in its nonlinear efficient range while the predistortion cancels out the resulting distortion, maintaining signal quality.
Solution Approach 2:
The patent employs feedback mechanisms to measure and compensate for amplifier nonlinearities. By monitoring the actual output signal and comparing it with the expected output, the system adjusts the predistortion coefficients dynamically. This feedback loop enables continuous optimization of the predistortion to match the amplifier's actual characteristics, resolving the contradiction between efficiency and distortion.
2Object-generated harmful factors
If the power amplifier is dimensioned to operate in a linear range to avoid intermodulation, then signal distortion is reduced, but device complexity and cost increase
Solution Approach 1:
The patent introduces a predistorter as an intermediary component between the signal source and the power amplifier. This intermediary circuit performs the function of linearization by applying inverse nonlinearities to the input signal. Instead of designing the amplifier itself to be linear (which would increase its complexity and cost), the predistorter handles the linearization task externally, keeping the amplifier simple and efficient.
3Object-generated harmful factors
If digital predistortion is applied to compensate for amplifier nonlinearities, then signal distortion is reduced, but computational complexity increases
Solution Approach 1:
The patent optimizes the predistortion by adjusting key parameters such as the order of the nonlinear model and the number of predistortion coefficients. Instead of using a complex high-order model that would require excessive computational resources, the system finds an optimal balance by changing these parameters. The model order is selected to provide sufficient distortion compensation while keeping the computational burden manageable for real-time operation.
Data Source
AI summary
An electrical network having a nonlinear transfer response is approximated with a system with memory. The system with memory being approximated in the frequency domain and subsequently being expanded in the time domain. A transfer response of the system being approximated to a transfer response of the electrical network in a range of a system bandwidth corresponding to an input signal bandwidth. The resulting model has adjustable parameters and can readily be implemented in the form of a dynamically linear filter and a static nonlinearity (B2) connected thereto.