Optical OFDM Receiver Nonlinearity Compensation via Digital Signal Processing

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Solution Overview

Problem

Optical OFDM systems face nonlinearity issues due to optical modulators, which affect signal quality and require costly solutions for compensation.

Innovation Solution

An optical OFDM receiver is designed with an optical down converter and a nonlinearity compensator that filters and demodulates electrical signals to address the distortion caused by optical modulators, eliminating the need for pre-distortion and enhancing modulation efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If optical modulators are used for converting baseband OFDM signal into optical signal band, then optical signal transmission is achieved, but nonlinearity distortion is introduced to the signal

Engineering Contradiction:

Improvesignal qualityVSAvoidnonlinearity distortion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful nonlinearity distortion into a measurable characteristic by capturing the distorted signal and processing it through an inverse discrete Fourier transform. The system then applies equalization techniques to compensate for the distortion, effectively converting the harmful nonlinearity into useful information for signal recovery and improvement.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent implements a feedback mechanism where the distorted optical signal is captured, converted to electrical signal, and processed through equalization algorithms. The equalized signal is then used to compensate for the nonlinearity effects, creating a closed-loop system that continuously corrects the distortion introduced by the optical modulator.

Inventive Principle:

Principle #23Feedback

2Reliability

If conventional solutions for compensating optical modulator nonlinearity are implemented, then signal distortion is reduced, but system cost increases

Engineering Contradiction:

Improvesignal qualityVSAvoidsystem cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces complex hardware-based nonlinearity compensation mechanisms with signal processing algorithms. Instead of using additional optical components or hardware equalizers, the system uses digital signal processing techniques including inverse discrete Fourier transform and equalization algorithms to achieve distortion compensation, thereby reducing system cost and complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the processing approach by applying inverse discrete Fourier transform and equalization parameters to the captured electrical signal. By adjusting equalization coefficients and processing parameters, the system achieves effective nonlinearity compensation without requiring additional hardware components, thus maintaining cost-effectiveness.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If pre-distortion techniques are used to compensate nonlinearity, then modulation efficiency is improved, but device complexity increases

Engineering Contradiction:

Improvemodulation efficiencyVSAvoidsystem complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

Instead of applying pre-distortion to the input signal before modulation, the patent applies post-equalization to the captured electrical signal after optical-to-electrical conversion. This inverted approach processes the signal in the reverse direction, using inverse discrete Fourier transform and equalization to compensate for nonlinearity effects, thereby achieving modulation efficiency improvement without adding complex pre-distortion hardware.

Inventive Principle:

Principle #13The other way round (Inversion)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively compensates for nonlinearity in optical modulators, improving signal robustness against channel distortion and increasing modulation efficiency without the need for pre-distortion, thus reducing costs and maintaining signal quality.

Implementation Method 1

an optical down converter converting the optical signal into an electrical signal

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS8521040B2Optical orthogonal frequency division multiplexing receiver and optical signal receiving method thereof

Publication Date: 2013.08.27 ELECTRONICS & TELECOMM RES INST

AI summary

Provided is an optical OFDM receiver. The optical OFDM receiver receives an optical signal dependent on the nonlinearity of a transmitter. The optical OFDM receives includes an optical down converter, a nonlinearity compensator, and an OFDM demodulator. The optical down converter converts the optical signal into an electrical signal. The nonlinearity compensator filters the electrical signal, for compensating distortion which is added to the optical signal when the transmitter performs optical modulation. The OFDM demodulator demodulates the distortion-compensated electrical signal in an OFDM scheme.