Opt Express. 2023 May 8;31(10):16812-16832. doi: 10.1364/OE.489530.
In this paper, we propose and evaluate two spatial division transmission (SDT) schemes, including spatial division diversity (SDD) and spatial division multiplexing (SDM), for underwater visible light communication (UVLC) systems. Moreover, three pairwise coding (PWC) schemes, including two one-dimensional PWC (1D-PWC) schemes, i.e., subcarrier PWC (SC-PWC) and spatial channel PWC (SCH-PWC), and one two-dimensional PWC (2D-PWC) scheme are further applied for signal-to-noise ratio (SNR) imbalance mitigation in the UVLC systems using SDD and SDM with orthogonal frequency division multiplexing (OFDM) modulation. The feasibility and superiority of applying SDD and SDM with various PWC schemes in a practical bandlimited two-channel OFDM-based UVLC system have been verified through both numerical simulations and hardware experiments. The obtained results show that the performance of SDD and SDM schemes are largely determined by both the overall SNR imbalance and the system spectral efficiency. Moreover, the experimental results demonstrate the robustness of SDM with 2D-PWC against bubble turbulence. Specifically, SDM with 2D-PWC can obtain bit error rates (BERs) under the 7% forward error correction (FEC) coding limit of 3.8 × 10 with a probability higher than 96% for a signal bandwidth of 70 MHz and a spectral efficiency of 8 bits/s/Hz, achieving an overall data rate of 560 Mbits/s.
本文提出并评估了两种适用于水下可见光通信（UVLC）系统的空分传输（SDT）方案，包括空分分集（SDD）和空分复用（SDM）。此外，还进一步应用了三种成对编码（PWC）方案，包括两种一维 PWC（1D-PWC）方案，即子载波 PWC（SC-PWC）和空间信道 PWC（SCH-PWC），以及一种二维 PWC（2D-PWC）方案，用于减轻采用正交频分复用（OFDM）调制的 SDD 和 SDM 中 SNR 不平衡的影响。通过数值仿真和硬件实验验证了在实际带限的基于两通道 OFDM 的 UVLC 系统中应用各种 PWC 方案的 SDD 和 SDM 的可行性和优越性。结果表明，SDD 和 SDM 方案的性能主要取决于总体 SNR 不平衡和系统频谱效率。此外，实验结果还证明了 2D-PWC 对气泡湍流具有鲁棒性。具体而言，2D-PWC 的 SDM 可以在 70MHz 信号带宽和 8bits/s/Hz 频谱效率下，在 7%前向纠错（FEC）编码限制下达到 3.8×10-3 的误码率（BER），概率高于 96%，实现了 560 Mbits/s 的总数据速率。
