Digital Predistortion Initialization for Wideband High-Power Amplifiers
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Solution Overview
Problem
Existing digital predistortion (DPD) methods face challenges in determining filter coefficients for nonlinear high-power amplifiers (HPAs), especially in wideband applications with strong nonlinearities, leading to distortion and interference.
Innovation Solution
A multi-step method using a nonlinear filter with adaptive coefficients, determined through an iterative process with multi-tone signals, to reduce intermodulation distortions and compensate for nonlinearities in HPAs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional DPD methods are used to determine filter coefficients, then the system complexity remains low, but the distortion compensation fails for strong nonlinearities and wideband applications
Solution Approach 1:
The initialization process is divided into multiple steps: first determining initial filter coefficients using a simplified linear method, then refining them through iterative adaptation. This segmentation allows the complex problem to be solved in manageable stages, achieving reliable distortion compensation without overwhelming system complexity.
Solution Approach 2:
The method performs preliminary determination of filter coefficients using a linear least-squares approach before applying iterative refinement. This preliminary action provides a good starting point that converges faster and more reliably, especially for wideband and strong nonlinearity scenarios where traditional methods fail.
2Ease of manufacture
If linear least-squares method is used to solve for filter coefficients, then the calculation is simple, but the method fails for nonlinear DPD applications
Solution Approach 1:
The coefficient determination is segmented into two phases: an initial linear least-squares phase that provides a closed-form solution for simplicity, followed by an iterative adaptation phase that handles the nonlinearities. This segmentation combines the advantages of both simple calculation and accurate nonlinearity compensation.
Solution Approach 2:
The linear least-squares method is applied as a preliminary step to obtain initial coefficients before nonlinear iterative refinement. This preliminary linear solution provides a computationally simple starting point that is then enhanced to handle strong nonlinearities and wideband conditions.
3Power
If DPD is applied to operate HPAs in nonlinear region for high output power, then the power efficiency improves, but the output signal becomes distorted with intermodulation and harmonic distortion
Solution Approach 1:
The DPD applies preliminary anti-action by pre-distorting the input signal with opposite characteristics to the HPA's nonlinear response. The filter coefficients are determined through iterative adaptation to minimize intermodulation distortion, allowing the HPA to operate in its nonlinear region for high power efficiency while the DPD pre-compensates for the resulting distortions.
4Adaptability or versatility
If DPD filter coefficients are not properly initialized, then the system remains simple, but the distortion compensation is not robust to different waveforms and frequencies
Solution Approach 1:
The initialization method uses dynamic iterative adaptation to adjust filter coefficients based on the actual HPA response to multi-tone test signals. This dynamic approach makes the DPD robust to different waveforms and frequencies by adapting to the specific characteristics of the HPA and input signal, rather than relying on fixed predetermined coefficients.
Data Source
AI summary
An apparatus and method are provided for digital predistortion of an electrical signal to pre-compensate for nonlinear distortions in a nonlinear channel (e.g., a nonlinear channel including a high-power amplifier). The digital predistortion processor includes a nonlinear filter. Filter coefficients are determined using a modified input electrical signal having multiple simultaneous tones, using an iterative process which adapts the modified input electrical signal to reduce levels of intermodulation distortions in a modified output electrical signal.