Zhou Yanting, Zhang Junwei, Lu Chao, Ghassemlooy Zabih, Guo Changjian
Opt Express. 2024 Feb 26;32(5):8081-8091. doi: 10.1364/OE.516562.
A digital pre-distortion (DPD) scheme based on an adaptive-memory-length look-up table (AML-LUT) is proposed and experimentally demonstrated in a four-level pulse amplitude modulation (4-PAM) underwater optical wireless communication (UOWC) system. By implementing adaptive memory length for each pattern in the AML-LUT-based DPD, the size of the AML-LUT can be significantly reduced without sacrificing performance compared to both the full-size LUT and the multi-symbol simplified look-up table (MSS-LUT)-based DPDs. The performance of the proposed AML-LUT-based DPD is experimentally evaluated for a 625 Mbit/s 4-PAM UOWC over 1 m transmission length. Experimental results show that compared with the full-size LUT with a memory length of 7 (LUT-7)-based DPD, the proposed AML-LUT-based DPD (i) incurs a marginal power penalty of 0.5 dB at both the 7% hard-decision forward error correction (HD-FEC) and KP4-FEC threshold limits, while simultaneously reducing the implementation complexity (i.e., the LUT size) by 93%; (ii) achieves comparable transmission performance compared to the MSS-LUT-based DPD, while reducing the implementation complexity by 89%; and (iii) shows great potential for high-speed, low-complexity and memory-efficient intensity modulation and direct detection (IM/DD) UOWC and short-reach optical interconnects.
提出了一种基于自适应存储长度查找表（AML-LUT）的数字预失真（DPD）方案，并在四电平脉冲幅度调制（4-PAM）水下光无线通信（UOWC）系统中进行了实验验证。通过在基于AML-LUT的DPD中为每个模式实现自适应存储长度，与全尺寸查找表和基于多符号简化查找表（MSS-LUT）的DPD相比，AML-LUT的大小可以显著减小，而不会牺牲性能。针对1 m传输长度的625 Mbit/s 4-PAM UOWC，对所提出的基于AML-LUT的DPD的性能进行了实验评估。实验结果表明，与基于存储长度为7的全尺寸查找表（LUT-7）的DPD相比，所提出的基于AML-LUT的DPD：（i）在7%硬判决前向纠错（HD-FEC）和KP4-FEC阈值限制下，功率代价仅为0.5 dB，同时实现复杂度（即查找表大小）降低了93%；（ii）与基于MSS-LUT的DPD相比，实现了相当的传输性能，同时实现复杂度降低了89%；（iii）在高速、低复杂度和内存高效的强度调制与直接检测（IM/DD）UOWC和短距离光互连方面显示出巨大潜力。
