OFDM Digital Pre-Distortion for Lower IBO Power Amplifiers
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Solution Overview
Problem
Power amplifiers in OFDM-based communication systems are inefficient due to non-linearity, leading to high energy consumption and increased costs, and require large Input Back Off (IBO) to manage Peak-to-Average Power Ratios (PAPR), which affects Error Vector Magnitude (EVM) and spectral mask compliance.
Innovation Solution
A digital pre-distortion method that computes weighting coefficients based on vector metrics and data tables to perturb OFDM symbols before transmission, reducing PAPR and optimizing energy consumption while maintaining spectral mask compliance, without separately treating real and imaginary parts of complex symbols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If Power Amplifier operates at high power to increase signal coverage, then transmission power is improved, but non-linearity increases causing distortion and inefficiency
Solution Approach 1:
The patent applies digital pre-distortion to the OFDM symbols before transmission. By computing weighting coefficients based on vector metrics and consulting predetermined data tables, the system predistorts the signal to compensate for PA non-linearity in advance, allowing the PA to operate at higher power while maintaining signal integrity
Solution Approach 2:
The patent modifies the signal parameters by applying complex weighting coefficients to OFDM symbols. These weighting coefficients are determined based on vector metrics and predetermined data tables, changing the signal characteristics to pre-compensate for power amplifier non-linearity and enable efficient high-power operation
2Reliability
If Input Back Off is increased to maintain linearity, then signal distortion is reduced, but power amplifier efficiency decreases and energy consumption increases
Solution Approach 1:
The system performs digital pre-distortion before transmission by computing weighting coefficients from predetermined data tables based on vector metrics. This preliminary compensation allows the PA to operate at optimal efficiency points without requiring large input back-off, thereby reducing energy consumption while maintaining linearity
Solution Approach 2:
The patent replaces the mechanical/power-based solution of increasing input back-off with a digital signal processing approach. By substituting power reduction with computational pre-distortion, the system maintains signal linearity while preserving power amplifier efficiency and reducing energy consumption
3Loss of energy
If digital pre-distortion is applied to reduce PAPR, then power amplifier efficiency is improved, but computational complexity increases
Solution Approach 1:
The patent computes weighting coefficients in advance and stores them in predetermined data tables organized by Modulation Coding Schemes and subcarrier subsets. During transmission, the system only needs to compute vector metrics and perform table lookups, significantly reducing real-time computational complexity while maintaining PAPR reduction effectiveness
Solution Approach 2:
The patent divides the frequency spectrum into multiple subsets of subcarriers and creates separate weighting coefficients for each subset. This segmentation allows the system to manage computational complexity by processing different subcarrier groups independently and using predetermined data tables for each MCS and subset combination
4Object-affected harmful factors
If weighting coefficients are optimized for spectral mask compliance, then spectral requirements are met, but Error Vector Magnitude performance may deteriorate
Solution Approach 1:
The patent applies different weighting coefficients to different subsets of subcarriers based on their spectral positions. By consulting predetermined data tables that are specific to each MCS and subcarrier subset, the system optimizes local signal characteristics to meet spectral mask requirements in specific frequency regions while maintaining overall EVM performance
Solution Approach 2:
The system dynamically selects weighting coefficients from predetermined data tables based on the Modulation Coding Scheme and subcarrier subset. This parameter adaptation allows optimization of spectral mask compliance for different modulation schemes and frequency regions while maintaining acceptable EVM performance through selective application of weighting coefficients
Data Source
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AI summary
RivieraWaves It is provided a method designed, for OFDM-based communication systems, to slightly modify the signal to be emitted before the power amplifier input of the transmitter. The guiding idea is that the minimal IBO value for which the slightly modified signal still fulfills the standard requirements is inferior to the smallest IBO value for which the transmitted signal still meets the standard requirements in terms of EVM and spectral mask without implementing the proposed method.