DSL Vectoring Precoder Adaptation for Disorderly Leaving Events
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Solution Overview
Problem
In DSL systems, Disorderly Leaving Events (DLEs) cause significant Signal to Noise Ratio (SNR) drops and service interruptions due to outdated precoders that fail to cancel crosstalk effectively, especially at higher frequencies, leading to retraining interruptions that can last several seconds.
Innovation Solution
A fast channel tracking mechanism is introduced, where error samples from other lines are used to estimate updated channel coefficients, allowing for a modified downstream precoder that minimizes errors and avoids retraining, using the model H′=H+CΛH to quickly adapt to sudden impedance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the precoder remains unchanged after a DLE, then the system maintains simplicity and continuity, but the SNR drops significantly due to outdated channel characteristics
Solution Approach 1:
The system performs preliminary channel estimation using error samples before fully updating the precoder. By estimating the channel coefficients H' using the model H'=H+CΛH and applying this estimation proactively, the system prevents SNR degradation before it occurs, rather than reacting after degradation has happened.
Solution Approach 2:
The system uses error samples from CPEs as feedback to estimate the changed channel coefficients. This feedback mechanism allows the precoder to adapt to DLE conditions by continuously monitoring error rates and adjusting channel estimates accordingly, maintaining SNR without requiring complete precoder reconfiguration.
2Measurement precision
If full retraining is performed after a DLE, then the channel characteristics are updated accurately, but service interruption increases due to lengthy retrain time
Solution Approach 1:
The system segments the channel estimation process into two parts: using the original channel estimate H for most frequencies and adding only the reflected crosstalk component CΛH for affected frequencies. This segmentation allows accurate channel tracking without requiring complete retraining of all channel characteristics, significantly reducing retrain time while maintaining precision where needed.
Solution Approach 2:
Instead of performing full channel retraining, the system applies partial action by estimating only the changed portion of the channel (the reflected crosstalk) using error samples. This partial estimation is sufficient to maintain service quality without the time cost of complete retraining, especially for higher frequencies where full retraining is most impactful.
3Measurement precision
If error samples are collected from all CPEs, then the channel estimate is comprehensive, but the processing time and complexity increase
Solution Approach 1:
The system applies local quality by estimating channel coefficients selectively - using error samples from CPEs only for the reflected crosstalk component CΛH rather than processing all channel characteristics uniformly. This localized estimation approach maintains sufficient precision for affected frequencies while significantly reducing processing time and complexity compared to full-channel analysis.
Data Source
AI summary
Vector Control Entity and method therein for Disorderly Leaving Events, DLEs, causing Sudden Termination Change in a DSL system. The method comprises, when a DLE occurs on a line m in a vectored group of DSL lines, and the transmission on line m is, at least partly, continued: obtaining at least one error sample from CPEs connected to other lines in the vectored group of DSL lines, and calculating an estimate of the channel coefficients, H′, changed due to the DLE. The estimate is calculated based on the at least one error sample, and thus a channel estimate is provided. The method further comprises modifying a downstream precoder, based on the channel estimate, such that retraining of the other lines in the vectored group due to the DLE is avoided. The estimate of the channel coefficients is calculated based on the model H′=H+CΛH.