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Gottfried (& others) – If you could put forward your preferred set of coefficients for the THP on long lines, I would like to double check our simulations. With the coefficients that were in your presentation, we are generally seeing MUCH worse results than you presented (using measured line models rather than your analytic models), and would like to check that we’re using the right forms. I want to make sure that what we’re seeing here is not the result of a “typo”.
When I look at other results, for example, Albert’s posting, the loss in performance due to the mismatch of a small set of THP coefficients relative to the actual impulse response is appearing significant – as Albert has pointed out.
If this continues to be the case, Seki’s earlier proposal (seki_1_0504.pdf) of an HDSL2-like coefficient exchange at startup (then fixing the coefficients) is becoming a more attractive alternative. The limiting the THP to a small set saves little hardware relative to the chip size, and seems to account for a significant robustness risk (at the least), or a much larger part of the performance margin budget than the hardware necessary to fix it would engender.
-george |