Abstract

A 60-GBaud intensity modulation and direct detection discrete Fourier transform spread (DFT-S) discrete multi-tone (DMT) transmission system employing low-density parity check- (LDPC-) encoded probabilistic shaping 16-ary quadrature amplitude modulation (PS-16QAM) is proposed and experimentally demonstrated. In contrast to classical probability-oriented PS schemes such as arithmetic distribution matching (ADM) and constant composition distribution matching (CCDM), the proposed one is performed based on a novel bit-weighted distribution matching (BWDM) algorithm having the advantage of simpler operations along with lower computation and hardware complexity, which merely relies on bit-class processing. As the key content of the BWDM, the bit weight intervention operation is utilized to enlarge the probability of bit ‘0’ in the first two out of four serial binary sequences before PS-16QAM mapping. Different from the labels indicating probability distribution in ADM and CCDM, the end product of the BWDM is a group of bits mapped from input data source, which can be seamlessly compatible with the following LDPC-based forward error correction. In our experiments, system performance is respectively investigated with three LDPC code rates (3/4, 5/6, and 9/10) as well as three PS parameter values (k = 4, 5, and 7), which leads to various symbol probability distribution. Compared with standard uniformly-distributed 16QAM, up to 0.407-dB shaping gain can be achieved to approach Shannon limit in the low signal-to-noise ratio region. Moreover, the experimental results show that appreciable receiver power sensitivity improvement can be obtained by the PS-16QAM DMT based on BWDM over 2-km standard single-mode fiber for short-reach optical interconnection. Additionally, the reference-based pre-equalization is equipped to compensate for the high frequency loss by ultra-wide signal bandwidth.

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