A Study of Error Correction Codes for PAM Signals in Data Center Applications

A study is presented through simulation and experiment on the proposed forward error correction (FEC) codes for data centers using higher order pulse amplitude modulation (PAM). The results highlight the tradeoffs in the adopted FEC approach for a fixed transmission link. Reed-Solomon (RS) and Bose-Chaudhuri-Hocquenghem (BCH) codes are considered in data center applications due to the low latency requirement budgeted for the encoding and decoding processes. Using Monte-Carlo and semi-analytical simulations, the signal to noise ratio requirement of PAM-N is obtained for a 500-m fiber transmission link at 100 Gb/s. For latency requirement under 100 ns, short-block RS codes offer possibly low complexity implementation with a pre-FEC bit error rate (BER) threshold at 8.8×10^-5. On the other end, BCH codes provide higher coding gain up to 9.3 dB with a BER threshold at 2.5×10^-3 at the expense of potentially longer decoding delay and complexity. An experimental investigation at 25 Gb/s for PAM-4 signal is performed to measure the actual net coding gain of the system. Results show that the performance of RS(578 514) code is within 1 dB of both BCH(3456 3084) and BCH(2464 2056) with 15% and 23% reduction in complexity, respectively.