PON Frame Guard Symbols for Modulation Format Transition Errors

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Solution Overview

Problem

Downstream passive optical networks face errors near frame boundaries due to mismatched modulation formats between transmitted and received signals, leading to increased bit error rates, particularly when using decision feedback equalizers or maximum likelihood sequence estimation equalizers.

Innovation Solution

Inserting guard symbols of a lower modulation format at the edges of frames of a higher modulation format to reduce bit error rates, which can be achieved by overwriting least significant bits of the higher modulation format symbols to convert them into the lower modulation format, or by interleaving codewords to distribute error clusters across multiple frames.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If modulation frames of different modulation formats are sent in the same frame structure, then communication versatility is improved, but bit error rate increases near frame boundaries

Engineering Contradiction:

Improvecommunication versatilityVSAvoidbit error rate

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies local quality by inserting guard symbols of a lower modulation format at specific positions (outer edges) within the frame structure. This creates a localized transition zone that helps receivers switch between different modulation formats smoothly, reducing errors at frame boundaries while maintaining the ability to communicate with multiple receiver types using different modulation formats.

Inventive Principle:

Principle #3Local quality

2Reliability

If guard symbols are inserted at frame edges to reduce errors, then reliability is improved, but frame overhead increases

Engineering Contradiction:

Improvebit error rateVSAvoidframe overhead

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent applies partial action by inserting guard symbols only at the outer edges of frames where modulation format transitions occur, rather than throughout the entire frame. This targeted approach provides sufficient error protection at critical transition points while minimizing the total number of guard symbols needed, thus reducing overhead while maintaining reliability.

Inventive Principle:

Principle #16Partial or excessive action

3Adaptability or versatility

If decision feedback equalizers are used to handle different modulation formats, then communication flexibility is improved, but error propagation near frame boundaries worsens

Engineering Contradiction:

Improvecommunication flexibilityVSAvoiderror propagation

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies beforehand cushioning by inserting guard symbols of a lower modulation format before the actual data transmission begins at frame boundaries. These guard symbols act as a cushion that allows decision feedback equalizers to adapt to the incoming signal format without causing error propagation, thereby maintaining communication flexibility while preventing error outbreaks at frame transitions.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS12081926B2Apparatus and a method for transmitting and receiving in a passive optical network

Publication Date: 2024.09.03 NOKIA SOLUTIONS & NETWORKS OY

AI summary

The method includes sending a first frame of a first modulation format that is suitable for a first group of receivers before sending a second frame of a second modulation format that is suitable for a second group of receivers, wherein the first modulation format is a higher modulation format than the second modulation format, and wherein the method further includes inserting into the first frame at least one symbol of the second modulation format at at least one outer edge of the first frame.