Transmitter Nonlinear Equalizer for QAM Signal Distortion
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Solution Overview
Problem
Devices experience signal distortions when power is increased, particularly due to nonlinear distortions introduced by drivers and semiconductor optical amplifiers (SOAs), which affect the performance of high-order quadrature amplitude modulation (QAM) constellation transponders.
Innovation Solution
The implementation of a transmitter nonlinear equalizer (TNE) using a reduced set of bits and a look-up table (LUT) to pre-compensate for nonlinear distortions, allowing for efficient digital pre-compensation and reducing the size of the LUT to improve practical implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power is increased to improve signal transmission, then output power is improved, but signal distortion increases due to nonlinear effects
Solution Approach 1:
The patent applies digital predistortion by pre-modifying the signal before transmission. A lookup table stores predistortion coefficients that compensate for nonlinear effects, and these coefficients are applied to the signal in advance to counteract the distortion that will occur during high-power transmission through the SOA.
2Object-affected harmful factors
If a traditional look-up table is used for predistortion, then signal distortion is reduced, but device complexity and memory requirements increase
Solution Approach 1:
The patent extracts only the essential bits needed for predistortion by analyzing which bits contribute most significantly to signal distortion. Instead of using all bits from the QAM constellation, the method identifies and processes only the most significant bits that have the greatest impact on nonlinear distortion, reducing memory requirements while maintaining effectiveness.
Solution Approach 2:
The patent applies different processing to different parts of the signal by separating bits based on their significance. The most significant bits are processed through the reduced lookup table for predistortion, while less significant bits are handled differently or omitted, creating a non-uniform processing approach that optimizes performance for the most critical signal components.
Data Source
AI summary
A method, system and apparatus for mapping a symbol from a N-QAM constellation into a binary bit set, where N is the number of symbols in the constellation, and reducing the length of the binary bit set according to at least one property of nonlinear distortion by generating a lookup table (LUT) address from a LUT address generator, and adding the LUT address to a LUT of size smaller than N{circumflex over ( )}(2M+1), where 2M is the number of neighboring symbols to be stored.