Constellation Extension Projection for OFDM PAPR Reduction
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Solution Overview
Problem
OFDM signals have a high Peak-to-Average Power Ratio (PAPR), making them sensitive to nonlinearities in High Power Amplifiers, which leads to In-Band distortions and Out-Of-Band interference, and existing PAPR reduction techniques are not optimal for non-square constellation patterns used in emerging systems like ATSC 3.0.
Innovation Solution
The solution involves coding a stream of input data into a constellation of symbols, applying a constellation extension projection in an outward angular region, and modulating the symbols to reduce PAPR, with the angle of the projection determined by the constellation type and forward error correction coding rate, allowing for efficient PAPR reduction while maintaining low complexity in encoding and decoding processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If OFDM modulation is used to achieve robust signal transmission and frequency diversity, then reliability is improved, but peak-to-average power ratio increases causing nonlinear distortions and interference
Solution Approach 1:
The patent applies preliminary action by performing constellation extension on the modulated symbols before OFDM modulation. The constellation extension process extends the constellation points in outward angular regions before the signal is transformed to time domain, proactively reducing peak values before they can cause nonlinear distortions in the power amplifier.
Solution Approach 2:
The patent changes the parameters of the constellation pattern by extending constellation points to new positions in outward angular regions. This parameter change modifies the signal distribution in the complex plane, which translates to reduced peak values in the time domain signal, thereby reducing PAPR while maintaining the robustness benefits of OFDM.
2Object-generated harmful factors
If conventional PAPR reduction techniques are applied, then peak-to-average power ratio is reduced, but performance degrades for non-square constellation patterns
Solution Approach 1:
The patent applies local quality by treating different constellation patterns (square vs. non-square) with different extension strategies. The constellation extension is adapted to the specific geometry of the constellation pattern, with extension angles and regions tailored to the particular modulation scheme being used, thereby maintaining optimal performance across different constellation types.
Solution Approach 2:
The patent introduces dynamics by making the constellation extension adaptive to the specific modulation scheme and signal conditions. The extension parameters (angles, regions, magnitude) are dynamically adjusted based on the constellation pattern type and code rate, allowing the system to optimize PAPR reduction for each specific configuration rather than using a fixed approach.
3Loss of energy
If constellation extension projection is applied to reduce PAPR, then amplifier efficiency is improved, but encoding complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the constellation extension process into distinct stages: determining extension angles based on constellation type, identifying which constellation points require extension, applying extension only to those specific points, and then proceeding with standard OFDM modulation. This segmented approach reduces complexity compared to a monolithic PAPR reduction technique.
Data Source
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AI summary
Methods and apparatuses for processing a signal that is transmitted with a reduced peak to average power ratio are described. The processing includes applying (1650) a symbol constellation extension projection to at least one symbol in the constellation, the symbol constellation extension projection having an outward angular region from an original position for the at least one symbol in the constellation, the outward angular region defined by a value for an angle between a first boundary and a second boundary for the outward angular region, the value for the angle determined by a selection of the constellation used as part of the transmitted signal and a code rate used for encoding the stream of data.