Optical Nyquist Filtering for OFDMA Overlay on Legacy PON

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Solution Overview

Problem

Legacy passive optical networks face interference issues between orthogonal frequency division multiple access (OFDMA) signals and filtered legacy on-off keying (OOK) signals, limiting transmission distance and split ratio due to the broad frequency response of OOK signals.

Innovation Solution

Implementing optical Nyquist filtering at the optical line terminal to suppress the harmonic components of OOK signals, preventing interference with OFDMA signals by using a narrow-band optical filter configured for Nyquist shaping, which allows for the combination of signals on a shared transmission medium without degrading the OOK signal performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If OOK signals are transmitted on legacy PON infrastructure, then existing optical networks can provide data signals, but the broad frequency response of OOK signals causes interference with OFDMA signals, limiting transmission distance and split ratio

Engineering Contradiction:

Improvecompatibility with legacy PON infrastructureVSAvoidinterference between OOK and OFDMA signals

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

An optical filter is introduced as an intermediary component in the optical path to selectively pass OFDMA signals while blocking OOK signal frequencies. This mediator enables coexistence of both signal types on the same legacy PON infrastructure without direct interference, resolving the contradiction between legacy compatibility and interference prevention.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The optical spectrum is segmented into distinct frequency bands: OOK signals occupy lower frequencies while OFDMA signals occupy higher frequencies. By dividing the frequency domain and assigning different bands to different signal types, the system eliminates spectral overlap and interference while maintaining compatibility with legacy infrastructure.

Inventive Principle:

Principle #1Segmentation

2Ease of manufacture

If OOK and OFDMA signals share the same transmission medium, then infrastructure cost is reduced, but interference between signals limits transmission distance and split ratio

Engineering Contradiction:

Improveinfrastructure costVSAvoidtransmission distance and split ratio

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The frequency spectrum is segmented to allocate different bands to OOK and OFDMA signals, with OOK occupying lower frequencies and OFDMA occupying higher frequencies. This spectral segmentation enables cost-effective shared infrastructure while eliminating interference that would otherwise limit transmission distance and split ratio.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An optical filter acts as a mediator that allows both signal types to coexist on the shared transmission medium. The filter selectively transmits OFDMA signals while blocking OOK signal frequencies, enabling infrastructure sharing without the reliability limitations caused by signal interference.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If colorless optical receivers are used to reduce cost, then receiver complexity is reduced, but interference between OOK and OFDMA signals cannot be effectively managed

Engineering Contradiction:

Improvereceiver complexityVSAvoidsignal interference

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

Interference prevention is performed in advance at the transmitter side using optical filtering, rather than requiring complex interference management at the receiver side. By pre-filtering OOK signals before they enter the shared medium, the system enables simple colorless receivers while still preventing interference, thus resolving the contradiction between receiver simplicity and interference management.

Inventive Principle:

Principle #10Preliminary action

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 significantly reduces bit error rates of OFDMA signals below the forward error correction limit while maintaining OOK signal performance, enabling longer transmission distances and higher split ratios by effectively filtering out interfering spectral components.

Implementation Method 1

filtering the second signal using an optical filter to suppress spectral components that would cause interference to the first signal

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Data Source

PatentUS9225421B2OFDMA overlay on legacy passive optical networks using optical nyquist filtering

Publication Date: 2015.12.29 NEC CORP

AI summary

Methods and systems for combining signals include modulating data onto a first signal at a first frequency and wavelength; modulating data onto a second signal at a second wavelength using a modulation scheme that produces spectral components at the first frequency; filtering the second signal using an optical filter to suppress spectral components that would cause interference to the first signal; and combining the first signal and the second signal onto a transmission medium.