Pre-Fec And Post-Fec Ber As Criteria For Optimizing Wireline Transceivers

Forward-error-correction (FEC) codes have become an integral part of high-speed wireline links. Signal-to-noise ratio, minimum mean-squared error, and pre-FEC BER are common performance metrics used to design and optimize link parameters, such as the tap coefficients in feed-forward and decision-feedback equalizers. This paper shows that the equalizer parameters found by conventional methods do not necessarily minimize post-FEC BER due to the unaccounted-for negative impact of DFE error propagation on FEC performance. However, the introduction of 1/(1+D) pre-coding eliminates long error bursts so that both pre-FEC and post-FEC BER are minimized with the same equalizer coefficients. These observations may have implications on the architecture and optimization of wireline transceivers.