Adaptive-memory-length look-up table (LUT)-based digital pre-distortion for IM/DD underwater wireless optical...

Area of Science:

• Optical Communications
• Signal Processing
• Wireless Networks

Background:

• Underwater optical wireless communication (UOWC) systems face challenges with signal distortion.
• Digital pre-distortion (DPD) is crucial for mitigating nonlinearities in intensity modulation and direct detection (IM/DD) systems.
• Existing DPD methods, like full-size look-up tables (LUTs) and multi-symbol simplified look-up tables (MSS-LUTs), can be complex and memory-intensive.

Purpose of the Study:

• To propose and experimentally demonstrate a novel adaptive-memory-length look-up table (AML-LUT)-based DPD scheme.
• To evaluate the performance and implementation complexity of the AML-LUT-based DPD in a 4-level pulse amplitude modulation (4-PAM) UOWC system.
• To compare the proposed AML-LUT DPD with existing DPD techniques in terms of performance and resource utilization.

Main Methods:

• Development of a DPD scheme utilizing an AML-LUT, where memory length is adaptively adjusted per pattern.
• Experimental setup for a 625 Mbit/s 4-PAM UOWC system over a 1-meter transmission.
• Evaluation of the AML-LUT DPD against full-size LUT (LUT-7) and MSS-LUT based DPDs, assessing power penalty and LUT size reduction.

Main Results:

• The AML-LUT-based DPD achieved a marginal 0.5 dB power penalty at 7% hard-decision forward error correction (HD-FEC) and KP4-FEC thresholds.
• Implementation complexity was reduced by 93% compared to LUT-7 DPD and 89% compared to MSS-LUT DPD.
• Comparable transmission performance was achieved with significantly lower complexity and memory requirements.

Conclusions:

• The proposed AML-LUT-based DPD offers a highly efficient solution for 4-PAM UOWC systems.
• This method significantly reduces implementation complexity and memory footprint without compromising system performance.
• The AML-LUT DPD shows strong potential for future high-speed, low-complexity, and memory-efficient UOWC and short-reach optical interconnects.