DSL Crosstalk Cancellation via Digital Filter
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Solution Overview
Problem
DSL communications are limited by crosstalk and narrow-band interference, which appear as both differential-mode and common-mode noise, affecting signal-to-noise ratio and data rate, and existing solutions require additional hardware or retraining of DSL links.
Innovation Solution
Implementing a digital filter at the receiving side of DSL modems with coefficients derived from autocorrelation and cross-correlation of common-mode and differential-mode signals during initialization and updated during active communication, to cancel crosstalk and RF interference without additional hardware or retraining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital filter with crosstalk cancellation is implemented, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The patent replaces physical hardware additions with digital signal processing algorithms. Specifically, it uses digital filtering techniques applied to the existing received signal to cancel crosstalk, substituting what would traditionally require additional physical cancellation hardware with computational methods implemented in the DSL modem's existing processing architecture.
Solution Approach 2:
The system uses its own received signal containing crosstalk to generate the cancellation filter coefficients through autocorrelation and cross-correlation calculations. The received signal itself serves as the source for creating the cancellation mechanism, eliminating the need for separate reference signals or additional hardware components.
2Object-affected harmful factors
If additional hardware is used for crosstalk cancellation, then crosstalk is reduced, but manufacturing cost increases
Solution Approach 1:
The patent eliminates the need for additional physical crosstalk cancellation hardware by implementing the cancellation function through digital signal processing algorithms in the existing modem architecture, thereby reducing manufacturing costs while maintaining effective crosstalk reduction.
Solution Approach 2:
The existing DSL modem processing architecture is made multi-functional by having it perform both standard signal reception and crosstalk cancellation using the same hardware resources, eliminating the need for dedicated cancellation hardware and reducing overall system cost.
3Object-affected harmful factors
If DSL link retraining is performed for crosstalk cancellation, then interference is reduced, but loss of time occurs
Solution Approach 1:
The patent calculates and applies crosstalk cancellation filter coefficients continuously during active communication without requiring periodic retraining interruptions. The system proactively maintains cancellation capability by using incoming signals to update coefficients in real-time, preventing interference buildup rather than reacting to it through retraining.
Solution Approach 2:
The crosstalk cancellation operates continuously during data transmission without interruption, maintaining interference reduction throughout the communication session rather than periodically resetting through retraining, thereby eliminating time loss while sustaining interference suppression.
4Measurement precision
If conventional crosstalk cancellation methods are used, then signal quality is improved, but adaptability to changing interference conditions deteriorates
Solution Approach 1:
The patent implements dynamic adaptation of crosstalk cancellation by continuously updating filter coefficients based on incoming signals during active communication. The system adapts to changing interference conditions in real-time rather than relying on static coefficients established during initialization, maintaining signal quality under varying channel conditions.
Solution Approach 2:
The system uses feedback from the received signals containing crosstalk to continuously refine the cancellation filter coefficients through correlation calculations. This feedback mechanism enables the system to automatically adapt to changing interference patterns and maintain optimal signal quality without manual intervention or retraining.
Data Source
AI summary
A digital subscriber line (DSL) modem that has a canceller digital filter for cancelling crosstalk and RF interference in a received DSL signal is disclosed. The modem includes common-mode sense circuitry and also differential-mode sense circuitry. Samples of the common-mode signal are acquired during a “quiet” period of initialization of the DSL modem, and samples of the differential-mode signal are acquired during live transmission of a DSL signal. An estimate of an autocorrelation function is obtained from the common-mode samples, and a cross-correlation of the common-mode samples and differential-mode samples is also estimated. Digital filter coefficients are derived from these estimates, based on the assumption that the common-mode samples acquired during the “quiet” phase represent crosstalk and RF interference present during differential-mode communications. The digital filter coefficients can also be updated during showtime of the DSL link, using an expanded number of samples of the common-mode and differential-mode signals.