ADC/DAC resolution tolerance improvement by implementing probabilistic shaping distribution in PAM and QAM modulation schemes

Abstract

In this paper, we simulated the ADC/DAC resolution tolerance improvement by implementing probabilistic shaping (PS) distributions in PAM and QAM modulation schemes for 400G and 800G transmissions. We compared PS- and uniformdistributed PM-16QAM, PM-32QAM, and PM-64QAM performance in 800G coherent transmission in FR links. The PS distribution scheme is based on Maxwell-Boltzmann distribution, and 0.1378 FEC overhead is chosen. We demonstrate that for any of these modulation schemes the post-BER (post-FEC bit-error rate) performance is more sensitive to ADC resolution. Moreover, the application of PS distribution can offer us 0.5-dB improvement in received optical power (ROP) for LDPC-coded PM-16QAM and 0.7-dB improvement for PM-32QAM, while PM-64QAM can get 0.6-dB improvement in ROP. For PAM transmission, we simulated a 4-channel CWDM 400G transmission system with wavelengths 1271 nm, 1291 nm, 1311 nm, and 1331 nm for 4-PAM modulation scheme. The PS distribution scheme we used in PAM is exponential distribution, and the FEC overhead is also 0.1378. We demonstrated that the pre-SER (pre-FEC symbol-error rate) performance is also more sensitive to the ADC resolution compared to DAC resolution. Therefore, the PS LPDCcoded modulation represents a great candidate to improve the system performance and reduce the cost.