Multicarrier Predistortion for Nonlinear Satellite HPA Distortion
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Solution Overview
Problem
High-throughput satellite communication systems face challenges in mitigating nonlinear distortion when using high-power amplifiers (HPAs) that operate at or near saturation, leading to intermodulation distortion and adjacent channel interference, which reduces spectral efficiency and power efficiency.
Innovation Solution
A multicarrier data predistortion technique is employed to estimate and compensate for distortion by modifying transmission symbols, allowing for successful transmission through nonlinear satellite channels, enabling efficient operation of HPAs near saturation with minimal IMD-induced clustering, and allowing for simple linear receivers to decode individual carrier signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high-power amplifiers operate at or near saturation to improve power efficiency, then power efficiency is improved, but intermodulation distortion and adjacent channel interference increase
Solution Approach 1:
The patent applies predistortion techniques that pre-compensate for nonlinear distortion by introducing an equal but opposite distortion before the signal enters the HPA. This preliminary anti-action cancels out the intermodulation distortion generated when the HPA operates near saturation, allowing the system to maintain both high power efficiency and low distortion levels.
Solution Approach 2:
The system performs preliminary channelization and filtering of the composite signal before it enters the HPA. By pre-processing the signal to separate carriers and apply individual filtering, the system reduces intermodulation distortion at the source while maintaining efficient HPA operation near saturation.
2Weight of stationary object
If multiple carriers share a common HPA to improve payload mass efficiency, then payload mass efficiency is improved, but intermodulation distortion and adjacent channel interference worsen
Solution Approach 1:
The patent segments the composite signal into individual carrier components through channelization filtering before amplification. By separating the carriers in the frequency domain and applying individual filtering to each, the system reduces intermodulation distortion between carriers while maintaining the benefits of shared HPA operation for payload mass efficiency.
Solution Approach 2:
The system performs preliminary channelization and filtering operations before the signal enters the shared HPA. This pre-processing separates the carriers and applies appropriate filtering to each, preventing intermodulation distortion from occurring in the first place while allowing efficient sharing of the amplifier across multiple carriers.
3Object-generated harmful factors
If significant back-off is applied to mitigate nonlinear distortion, then intermodulation distortion is reduced, but amplification efficiency is lost
Solution Approach 1:
Instead of reducing the input power to the HPA (back-off) to avoid nonlinear distortion, the patent applies predistortion that pre-compensates for the expected distortion. This allows the HPA to operate at full power with high efficiency while the predistortion ensures that the output distortion is cancelled out, achieving both low distortion and high amplification efficiency.
4Area of stationary object
If high-order modulations are used to improve spectral efficiency, then spectral efficiency is improved, but susceptibility to nonlinear distortion increases
Solution Approach 1:
The patent applies predistortion techniques that pre-compensate for nonlinear distortion effects on high-order modulation signals. By introducing equal but opposite distortion before the HPA, the system protects the delicate constellation points of high-order modulations (like 16-APSK and 32-APSK) from degradation, enabling these spectrally efficient modulations to be used without suffering from nonlinear distortion.
Data Source
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AI summary
An approach for improved compensation for nonlinear distortion in multicarrier satellite systems is provided. Source reflecting encoded and modulated sequences of source data symbols are received. Each source signal is predistorted, and a transmit filter is applied to each predistorted source signal. Each filtered signal is translated to a carrier frequency, and the translated signals are combined into a composite signal for transmission via a multicarrier transponder. The final predistorted version of each source signal is generated via an iterative process of a number of stages, wherein, for a given stage and for each source signal, the process comprises: receiving a prior predistorted version of each source signal from a preceding stage; processing each prior predistorted source signal based on all of the received prior predistorted source signals, wherein the processing is performed based on a characterization of one or more characteristics of the multicarrier satellite transponder.