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In Hossain’s presentation today, it was mentioned that the clipping probability was set to about the target DER. I did not comment on that due to the expected length of the other Q&A. In my experience, ADC clipping is a source of large errors that have a high probability of creating errors. Moreover, clipping events are often related to low-frequency effects such as baseline wander and/or long runs of outer symbols. Thus the errors created are correlated and can severely impact the FEC performance. As a result, in practice, gain control loops for ADC drive to have much lower probability of clipping than the allowed BER; I’ve never seen anything higher than 1e-6 in FEC-aware receivers, and even 1e-9 is common. I think the high clipping probability also allows signals with large peak-to-average ratio at the ADC input, which may explain why Tx equalization is not used. When Tx equalization is used together with the CTLE, the distribution would be more bounded and allow for much lower clipping probability for a given quantization noise. The straw polls did not include the detail of clipping probability; We need to adopt a value. I would recommend starting with a moderately conservative assumption of 3 orders of magnitude below DER0. Further analysis would be required and welcome. </Adee> To unsubscribe from the STDS-802-3-B400G-ELEC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-B400G-ELEC&A=1 |
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