DSL FEXT Estimation Using NEXT and Line Transfer Functions

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Solution Overview

Problem

Current DSL systems face challenges in accurately measuring and managing FEXT interference between lines without direct measurement, leading to inefficient spectrum use and performance limitations due to static management rules and assumptions about worst-case scenarios.

Innovation Solution

The method calculates FEXT interference using measurable NEXT interference and downstream channel transfer function data available at the upstream end of DSL loops, employing linear or logarithmic operations to approximate FEXT, which can be performed by a system controller like a DSL optimizer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If direct measurement of FEXT interference is performed, then measurement precision is improved, but device complexity and system disruption increase

Engineering Contradiction:

ImproveFEXT interference measurement accuracyVSAvoidmeasurement system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses NEXT interference measurement and downstream channel transfer function as intermediary measurements to indirectly determine FEXT interference. Instead of directly measuring FEXT, the system measures NEXT at the upstream end and combines it with channel transfer function data to calculate FEXT, thereby avoiding the complexity of direct FEXT measurement while maintaining accuracy

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct physical measurement of FEXT with a computational approach. By using the relationship FEXT ≈ NEXT × H (where H is the downstream channel transfer function), the system substitutes complex measurement hardware and procedures with mathematical calculation based on readily available data

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If static spectrum management rules are used, then system complexity is reduced, but adaptability and performance deteriorate

Engineering Contradiction:

Improvespectrum management complexityVSAvoidspectrum management adaptability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent implements dynamic spectrum management by continuously measuring NEXT interference and channel transfer functions during normal operation, then using these real-time measurements to calculate and adjust FEXT compensation. This dynamic approach replaces static worst-case assumptions with actual measured conditions, improving adaptability while maintaining manageable complexity through automated calculations

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system establishes a feedback loop where NEXT measurements and channel transfer function data are continuously collected, processed to determine FEXT interference, and used to adjust spectrum management decisions. This feedback mechanism enables the system to adapt to changing line conditions automatically, improving performance without requiring complex manual intervention

Inventive Principle:

Principle #23Feedback

3Reliability

If FEXT measurement and removal is implemented, then signal quality is improved, but loss of time and operational disruption increase

Engineering Contradiction:

Improvesignal qualityVSAvoidsystem operational time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent performs FEXT determination during normal system operation using data that is already being collected for other purposes (NEXT measurements and channel transfer functions). By utilizing these pre-existing measurements to calculate FEXT, the system determines interference levels without requiring separate measurement procedures, thus avoiding operational disruption and time loss

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses its own operational data (NEXT measurements and channel transfer functions that are already being collected during normal DSL operation) to determine FEXT interference. This self-service approach eliminates the need for external measurement equipment or specialized test procedures, maintaining continuous operation while improving signal quality

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS7593458B2FEXT determination system

Publication Date: 2009.09.22 ADAPTIVE SPECTRUM AND SIGNAL ALIGNMENT INC(US)

AI summary

Operational data is utilized to determine the FEXT interference induced by one line into the other DSL line. FEXT interference can be calculated using the NEXT interference measured between the two lines at the upstream ends of the loops and the downstream channel transfer function of one of the loops. Because the NEXT and transfer function constitute a linear time-invariant system, as does the FEXT interference between the lines, the NEXT interference and line transfer function can be multiplied (if in linear format) or added (if in logarithmic format) to approximate the FEXT interference between the lines. The collection of data, calculations and other functions performed in these techniques may be performed by a system controller, such as a DSL optimizer. An Xlog(u,n) quantity is a decibel-magnitude representation of the insertion-loss equivalent of FEXT transfer functions and is defined as the ratio of (1) a line u's source power into a matched load of 100 Ohms when no binder is present to (2) the power at the output of the subject line when line u is excited with the same source and the binder is present. Xlin(u,n) is the linear equivalent of Xlog(u,n). The Xlog(u,n) and Xlin(u,n) quantities may be represented in specific formats that assist in their use in DSL and other systems. When defined as a line's insertion loss, Xlin (or equivalently Xlog) does not include the effect of any transmit filter.