TDMA FEXT Channel Estimation in DSL Systems
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Solution Overview
Problem
In DSL systems, far-end crosstalk (FEXT) interference limits data rates due to increased training time and stronger signal levels, especially at higher frequency bands, making existing FEXT compensation methods less effective.
Innovation Solution
A DSLAM is configured to allocate specific time slots for FEXT channel estimation, where training symbols are transmitted on one subscriber line while the other line is quiet, and feedback symbols are received to estimate FEXT levels, improving estimation speed and performance using a time division multiple access (TDMA) approach.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FEXT training signal is sent during sync symbol with orthogonal sequence modulation, then FEXT channel estimation can be performed, but training time increases and FEXT level becomes stronger than received data signal
Solution Approach 1:
The patent segments the FEXT estimation process into two distinct phases: upstream FEXT estimation using upstream training symbols, and downstream FEXT estimation using downstream training symbols. This segmentation allows each phase to be optimized independently, reducing overall training time while maintaining estimation accuracy.
Solution Approach 2:
The patent performs preliminary FEXT channel estimation during the training phase before actual data transmission begins. By establishing FEXT channel estimates in advance using dedicated training symbols, the system avoids the need for continuous FEXT estimation during data transmission, thereby reducing training time overhead.
2Productivity
If orthogonal sequence modulation is used for FEXT training signal, then multiple subscriber lines can be trained simultaneously, but FEXT level becomes stronger and equalizer training fails
Solution Approach 1:
The patent extracts and separates the FEXT estimation function from the main data transmission process. By using dedicated FEXT training symbols transmitted during upstream and downstream phases, the system isolates FEXT estimation from data signal reception, allowing accurate FEXT measurement even when FEXT levels are high without interfering with normal data operations.
Solution Approach 2:
The patent introduces FEXT training symbols as intermediary signals that facilitate FEXT channel estimation without using the actual data signals. These intermediary training symbols are specifically designed for FEXT measurement purposes, allowing the system to estimate FEXT channels without the harmful effects of strong FEXT interfering with data reception.
3Power
If high frequency band edge is increased to 100 MHz or higher, then channel capacity increases, but FEXT becomes relatively stronger and training problem worsens
Solution Approach 1:
The patent implements periodic FEXT training at specific intervals during upstream and downstream transmission phases. By periodically inserting FEXT training symbols at predetermined intervals rather than continuously, the system maintains accurate FEXT channel estimates for high frequency operations while minimizing the impact of strong FEXT on data transmission.
Data Source
AI summary
A method of far-end crosstalk (FEXT) channel estimation in a digital subscriber line (DSL) system, wherein the DSL system comprises a first subscriber line and a second subscriber line, the method comprising allocating a plurality of time slots, wherein the plurality of time slots comprises a first period and a second period, wherein the first period precedes the second period, and wherein each of the first and second periods comprises at least one time slot, transmitting at least one training symbol in the first period onto the second subscriber line in a downstream direction while no transmission is made on the first subscriber line, receiving at least one feedback symbol in the second period from the first subscriber line in an upstream direction, and estimating a level of downstream FEXT from the second subscriber line into the first subscriber line based on the at least one feedback symbol.