Forward Error Correction Challenges in 400G Device Test
White Papers
As data rates increase, so do the challenges of device design, validation, and test. The use of 4-level pulse amplitude modulation (PAM4) signaling has changed Ethernet test requirements. Due to the reduced signal to noise ratio (SNR), PAM4 links do not necessarily run error-free and require forward error correction (FEC). FEC is an advanced coding technique that sends the required information to correct errors through the link along with the payload data. The benefit of “forward” in FEC is that there is no need to retransmit information to correct errors detected at the receiver.
FEC is especially beneficial in applications where retransmissions are costly or impossible, such as one-way communication links and transitions to multiple receivers in data centers. The FEC technique controls errors in data transmissions over unreliable or noisy channels. FEC transforms transmitted data (message sequences) into code words that include redundant data. The receiver decoder uses the added redundancy to detect, and possibly correct, errors that may occur in the message, minimizing the need to retransmit.