With the fast growth of 5G/6G networks and AI/ML applications, serial link data rates continue to increase due to high-speed communication and large bandwidth demands. Recently the IEEE 802.3 has established a 200 Gbps, 400Gbps, 800 Gbps and 1.6 Tbps Ethernet task force 802.3dj. The new task force is aiming at 200 Gbps per lane link rate, doubled from the 100 Gbps per lane rate.

A decade ago, the semiconductor industry successfully updated signaling formats from NRZ to PAM4 during the transition from 25 Gbps to 50 Gbps link rates. To offset the signal-to-noise ratio penalty caused by higher modulation levels, forward error correction (FEC) has become an essential part of the solution for PAM4 systems. This paper follows and builds from two previous papers: “What is FEC and how do I use it?”¹ and “100+ Gbps Ethernet Forward Error Correction (FEC) Analysis)”², and provides updates for the next generation Ethernet rate, 200+ Gbps per lane.

In order to study what is needed and what has been adopted for the next Ethernet speed node of 200 Gbps per lane, this paper investigates different FEC schemes such as end-end, concatenated, and segmented FECs, and how these different FEC schemes affect signal integrity and performance in different end applications. 

With the latest decision made within the IEEE 802.3dj task force, in which the Hamming (128,120) inner code has been adopted as a part of the FEC solution for 200 G/s per lane PAM4 optics, concatenated FEC modeling and performance analysis have become key to multiple-part link system analysis including the optical channel and two or more electrical channels. 

Since inner code, miss-correction is highly undesirable for overall concatenated FEC performance, its cause, impact, and mitigation schemes are investigate in. Furthermore, soft decision decoding is recommended to achieve better coding gain. To break the long burst errors and improve concatenated code performance, there are multiple interleaving schemes proposed for inner code sublayer.

The proposal claims that the inner Hamming code (128, 120) with the above three interleaving functions could relax the optical BER target from 2.4e-4 to 4.8e-3, more than one order of magnitude.

REFERENCES

1. C. Liu, “What is FEC, and How Do I Use It?”, Signal Integrity Journal, July 1, 2019.
2. C. Liu, “100+ Gb/s Ethernet Forward Error Correction (FEC) Analysis,” Signal Integrity Journal, July 9, 2019.

The paper referenced here received the Best Paper Award at DesignCon 2024. To read the entire DesignCon 2024 paper, download the PDF.