Decision Feedback Equalizer with Marginal Symbol Suppression

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Solution Overview

Problem

Conventional decision feedback equalizers in digital data transmission systems can exacerbate errors through recursive feedback, leading to burst errors, particularly in multilevel and multidimensional modulation techniques like 4-PAM and QAM, due to the compounding of post-cursor intersymbol interference.

Innovation Solution

A burst error limiting symbol detector system that includes a symbol detector circuit, a feedback equalizer circuit, and a feedback modification circuit to prevent marginal detected symbols from entering the feedback loop, using intermediate values or original symbol values instead of adjusted feedback values when the corrected sample signal falls within marginal threshold windows.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional decision feedback equalizer is used to cancel post-cursor intersymbol interference, then equalization performance is improved, but burst errors are exacerbated due to recursive feedback

Engineering Contradiction:

Improveequalization performanceVSAvoidburst errors

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary mechanism (feedback modification circuit) between the symbol detector and feedback equalizer that detects marginal symbols and substitutes them with intermediate values before they enter the feedback loop. This mediator prevents harmful marginal symbols from propagating through the recursive feedback system while maintaining the beneficial equalization performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the feedback parameter by substituting marginal symbol values with intermediate values (e.g., zero or averaged values) before feeding them back to the equalizer. This parameter modification prevents the amplification of errors through the recursive feedback system while preserving the equalization function.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If feedback equalizer uses detected symbols for cancellation, then intersymbol interference is reduced, but error propagation occurs through recursive feedback

Engineering Contradiction:

Improvesymbol detection accuracyVSAvoiderror propagation

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent applies preliminary action by detecting marginal symbols before they enter the feedback loop and substituting them with intermediate values in advance. This preemptive measure prevents error propagation before it can occur through the recursive feedback system.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The feedback modification circuit acts as an intermediary that filters detected symbols before they are used in the feedback cancellation process. It identifies problematic marginal symbols and replaces them with safe intermediate values, preventing error propagation while maintaining accurate symbol detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If marginal symbols are fed back to feedback equalizer, then feedback loop maintains continuity, but distortion is compounded leading to burst errors

Engineering Contradiction:

Improvefeedback loop continuityVSAvoiddistortion compounding

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The patent changes the feedback parameter by replacing marginal symbol values with intermediate values (such as zero or averaged values) before they are fed back to the equalizer. This parameter substitution maintains the continuity of the feedback loop while preventing the compounding of distortion that would occur with marginal symbols.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful marginal symbols into beneficial intermediate values that maintain feedback loop continuity without causing distortion compounding. By substituting marginal symbols with neutral intermediate values, the system transforms a harmful element into a benign one that preserves system stability.

Inventive Principle:

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

Data Source

PatentUS7522663B2Burst error limiting feedback equalizer system and method for multidimensional modulation systems

Publication Date: 2009.04.21 STMICROELECTRONICS INT NV

AI summary

A burst error limiting symbol detector system includes a symbol detector circuit responsive to a corrected sample signal for detecting multilevel or multidimensional symbols encoded in the corrected sample signal with reference to a plurality of associated thresholds. A feedback equalizer circuit provides a feedback equalizer signal for cancelling undesired distortion in an input signal. A summing circuit is responsive to the input signal and the feedback equalizer signal to provide the corrected sample signal to the symbol detector circuit. A feedback modification circuit is responsive to the corrected sample being within one of a plurality of valid symbol windows to feed back the detected symbol to the feedback equalizer and is responsive to the corrected sample being within one of plurality of marginal threshold windows to feed back a corresponding intermediate value to the feedback equalizer.