Multiband Digital Predistortion for HPA Spectral Regrowth Control
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Solution Overview
Problem
Conventional RF transmitters face challenges in managing non-linear distortion in high-power amplifiers (HPAs) due to high sampling rate requirements and inefficiencies in broadband applications, particularly when operating near saturation, leading to spectral regrowth and in-band distortion.
Innovation Solution
Implementing multiband digital predistortion (mDPD) that segments the signal spectrum into multiple frequency sub-bands, compensating for both in-band and cross-band distortions, thereby reducing sampling rate requirements and enhancing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single-band DPD is applied on the full signal spectrum, then non-linear distortion compensation is achieved, but sampling rates must be four to eight times the full signal bandwidth which increases cost and complexity
Solution Approach 1:
The patent divides the wideband input signal into multiple narrowband sub-signals using a segmenter, where each sub-signal corresponds to a specific frequency sub-band. This segmentation allows each sub-band to be processed independently by separate DPD processors, reducing the sampling rate requirement from four to eight times the full bandwidth to a manageable rate suitable for narrowband processing, while still achieving comprehensive distortion compensation across the entire spectrum through combination of processed sub-signals
2Use of energy by moving object
If high-power amplifier is driven near saturation to achieve power efficiency, then power efficiency is improved, but non-linear distortion increases causing spectral regrowth and in-band distortion
Solution Approach 1:
The patent applies digital predistortion processing to each narrowband sub-signal before the signals are combined and amplified by the HPA. By pre-compensating each sub-band for the expected non-linear distortion that will occur when the HPA operates near saturation, the system maintains power efficiency while minimizing the generation of spectral regrowth and in-band distortion. The predistorted sub-signals, when processed by the saturated HPA, produce minimal overall distortion
3Reliability
If multi-band DPD is implemented to compensate for cross-band interactions, then linearization performance is improved, but processing complexity increases
Solution Approach 1:
The patent segments the broadband signal into multiple narrowband sub-signals that can be processed in parallel by separate DPD processors. Each processor handles only its assigned sub-band, significantly reducing individual processing complexity compared to processing the entire broadband signal simultaneously. The segmenter and combiner coordinate these parallel processing streams, achieving comprehensive linearization including cross-band interaction compensation while maintaining manageable processing complexity through the divide-and-conquer approach
Data Source
AI summary
Techniques are described for implementing multiband digital predistortion in a broadband transmitter in a manner that provides effective compensation of non-linear distortion arising from integration of a high-power amplifier (HPA). Embodiments segment the signal spectrum of a transmit signal into multiple sub-band signals and apply non-linear distortion compensation separately and concurrently for each sub-band signal. The resulting multi-band digital predistortion (mDPD) compensates both for in-band distortion and for distortions from non-linear interactions between the frequency sub-bands. The disclosed mDPD can provide enhanced performance features, such as handling of memory effects, reduced sampling rate requirements for DPD components, and minimizing detrimental spectral regrowth at the HPA output.