Decoding of 10-G Optics-Based 50-Gb/s PAM-4 Signal Using Simplified MLSE

A simplified maximum likelihood sequence estimation (MLSE) based on Viterbi algorithm has been proposed. Experimental results show that compared with the conventional MLSE, the proposed algorithm saves the multiplication by 25% with no sensitivity penalty when the memory length of MLSE is 2 both in the 25 Gb/s nonreturn to zero and 50 Gb/s four-level pulse-amplitude modulation (PAM-4) transmission systems. In order to further reduce the number of multiplications in the 50 Gb/s PAM-4 transmission system, we use 75 taps of feed-forward equalization to equalize the received PAM-4 signal into duo-binary PAM-4 (DB-PAM-4) signal and then use MLSE with the memory length of 1 to decode, which improves the sensitivity performance by 1.8 dB and reduces the computing complexity by ~98% compared with conventional MLSE (L = 4) method. As a result, a 10-km C-band transmission of 50 Gb/s PAM-4 signal is achieved using optical transceivers with a combined 3-dB bandwidth of ~8 GHz, and only 107 multiplications are required by using our proposed simplified algorithm for equalization.