Probabilistic Constellation Shaping Research Articles

Discrete multitone transmission for underwater optical wireless communication system using probabilistic constellation shaping to approach channel capacity limit.

Probabilistic constellation shaping (PCS) is utilized to approach the channel capacity limit in discrete multitone (DMT) transmission for underwater optical wireless communication (UOWC) system. A fixed quadrature amplitude modulation (QAM) format with various probabilistic distributions is individually allocated for different subcarriers to obtain achievable maximum channel capacity in accordance with the pre-estimated signal-to-noise ratio. By using a 450-nm directly modulated laser diode (LD) with an available modulation bandwidth of ∼2.75 GHz, DMT with PCS technique is experimentally realized with a net data rate of 18.09Gbit/s over 5m, 17.21Gbit/s over 25m, and 12.62Gbit/s over 35m underwater transmission, giving substantial capacity improvement of 32.22%, 30.03%, and 27.55%, respectively, in comparison with the widely used regular QAM formats in DMT with bit-power loading scheme. The figure of merit of the UOWC system in terms of entropy, generalized mutual information (GMI), and normalized GMI are also presented. To the best of our knowledge, this is the first time to employ PCS-QAM-DMT in a UOWC system, and it is also the highest data rate ever reported for a single LD in UOWC.

High-speed underwater wireless optical communications: from a perspective of advanced modulation formats [Invited

In this paper, recent advances in underwater wireless optical communication (UWOC) are reviewed for both LED- and LD-based systems, mainly from a perspective of advanced modulation formats. Volterra series-based nonlinear equalizers, which can effectively counteract the nonlinear impairments induced by the UWOC system components, are discussed and experimentally demonstrated. Both the effectiveness and robustness of the proposed Volterra nonlinear equalizer in UWOC systems under different water turbidities are validated. To further approach the Shannon capacity limit of the UWOC system, the probabilistic constellation shaping technique is introduced, which can overcome the inherent gap between a conventional regular quadrature amplitude modulation (QAM) format and the Shannon capacity of the channel. The experimental results have shown a significant system capacity improvement compared to the cases using a regular QAM.

25.4-Tb/s Transmission Over Transpacific Distances Using Truncated Probabilistically Shaped PDM-64QAM

Probabilistic constellation shaping (PCS), digital nonlinear compensation, and multirate spatially coupled low-density parity check codes are used to achieve 25.4-Tb/s transmission over 10 285 km EDFA-only straight-line testbed at 6.1 bits/symbol/Hz. The gain provided by PCS over standard 64QAM is investigated over transatlantic and transpacific distances. Moreover, the potential benefits of nonlinear compensation based on digital-backpropagation versus algorithm complexity are addressed.