Joint Multicarrier Pre-Distortion for Repeater Nonlinearities
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Satellite communication systems face significant challenges due to nonlinearities in communication channels, particularly in multiple carrier systems where joint amplification leads to spurious inter-modulation products and distortions such as adjacent-channel interference and intersymbol interference, resulting in performance degradation and inefficiencies in power and spectral usage.
Innovation Solution
A method and system utilizing a gateway transmitter that applies pre-distortion to digital signals before frequency division multiplexing, using polynomial functions with coefficients computed via a direct learning approach, to mitigate nonlinearities in communication channels. This involves modulating digital signals on multiple carriers, distorting symbols based on a pre-distortion function, and iteratively updating coefficients based on feedback from receivers to enhance non-linearity compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If joint amplification of multiple carriers is used to save payload mass and reduce hardware complexity, then device complexity and payload mass are reduced, but spurious inter-modulation products and distortions occur causing performance degradation
Solution Approach 1:
The patent applies digital pre-distortion at the gateway transmitter before signal transmission to anticipate and compensate for the nonlinear distortions that will occur during joint amplification on the satellite. By pre-compensating the signals with inverse distortion characteristics, the system maintains link performance while utilizing joint amplification to reduce payload complexity
Solution Approach 2:
The patent implements an iterative feedback mechanism where the gateway transmitter receives feedback signals from the satellite or ground stations about the actual channel conditions and distortion levels. This feedback is used to continuously update and refine the pre-distortion coefficients, ensuring optimal compensation for the nonlinearities in the communication channel
2Reliability
If amplifier is operated in linear region to avoid nonlinear distortions, then link performance is maintained, but power efficiency is reduced compared to single carrier operations
Solution Approach 1:
The patent applies digital pre-distortion at the gateway transmitter before signal transmission to anticipate and compensate for the nonlinear distortions that will occur during joint amplification on the satellite. By pre-compensating the signals with inverse distortion characteristics, the system maintains link performance while utilizing joint amplification to reduce payload complexity
Solution Approach 2:
The patent dynamically adjusts the pre-distortion coefficients based on the operating conditions, amplifier back-off levels, and channel characteristics. By optimizing these parameters, the system can operate the amplifier in a more efficient nonlinear region while maintaining performance through compensation, thereby improving power efficiency compared to conservative linear operation
3Object-affected harmful factors
If large guard-band between carriers is used to avoid adjacent-channel interference, then spectral efficiency is reduced, but interference from other carriers is minimized
Solution Approach 1:
The patent applies digital pre-distortion at the gateway transmitter before signal transmission to anticipate and compensate for the nonlinear distortions that will occur during joint amplification on the satellite. By pre-compensating the signals with inverse distortion characteristics, the system maintains link performance while utilizing joint amplification to reduce payload complexity
Solution Approach 2:
The patent converts the harmful inter-modulation products and adjacent-channel interference caused by joint amplification into beneficial information by measuring the actual distortion characteristics and using them to compute accurate pre-distortion coefficients. The previously harmful nonlinear effects become the basis for precise compensation, allowing tight carrier spacing without performance degradation
4Object-affected harmful factors
If single carrier techniques are used to avoid inter-modulation products, then spectral efficiency is reduced, but nonlinear distortions are avoided
Solution Approach 1:
The patent applies digital pre-distortion at the gateway transmitter before signal transmission to anticipate and compensate for the nonlinear distortions that will occur during joint amplification on the satellite. By pre-compensating the signals with inverse distortion characteristics, the system maintains link performance while utilizing joint amplification to reduce payload complexity
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
A method, carried out by a gateway transmitter (400), aims at compensating the nonlinearities of a communication channel (500) comprising a repeater (510). A plurality of digital signals is modulated (s10) on a plurality of carriers, wherein symbols of the constellation diagram used for modulation of each carrier are distorted in accordance with a pre-distortion function. The modulated signals are then frequency division multiplexed (s20), and sent (s30) for transmission, through the communication channel (500), to at least one receiver (600). The pre-distortion function involves a plurality of polynomial functions, each of which taking as input the symbols from all the carriers. The polynomial functions' coefficients, called "pre-distortion coefficients", are computed according to a direct learning approach, performed jointly for the plurality of carriers. The pre-distortion coefficients are iteratively updated based on received signals being fed back from a receiver (600). The invention also relates to transmitters and computer programs.