Abstract

In this paper, we first utilize the interleaved single-carrier frequency division multiplexing (I-SC-FDM) scheme with a novel sparse weight-initiated deep neural network (SWI-DNN) equalizer for underwater optical communication (UWOC) systems. In addition to the superior characteristics of I-SC-FDM over the original OFDM and localized SC-FDM (L-SC-FDM), such as lower peak-to-average power ratio (PAPR) and lower computational complexity, the implementation of a special sparse weight-initiated (SWI) structure can significantly reduce the necessary training epochs up to 10.3%, which enables the proposed SWI-DNN equalizer to outperform the traditional random weight-initiated DNN equalizer. Besides, further pruning operation can dramatically enhance the final sparsity of the SWI-DNN equalizer to 96.88% at the expense of an inappreciable performance penalty, thereby effectively saving occupied computing resources. Following this, a data rate of up to 660 Mbps over a 90-m underwater transmission can be achieved in a standard 50-m swimming pool, with a relatively low received optical power of −31.12 dBm (at the BER of 3.8 × 10⁻³). Such a data rate is 17.9% higher than that obtained with a common hybrid time-frequency domain (TFD) equalizer. Moreover, the computational complexity of the SWI-DNN equalizer after pruning operation is only 11.83% of that of the hybrid TFD equalizer and can still support a 625-Mbps transmission. This is the first time to employ I-SC-FDM combined with an SWI-DNN equalizer for long-distance high-speed UWOC transmission, and it can be highly beneficial to the cost-sensitive and power-sensitive systems in future deployment.

200-m/500-Mbps underwater wireless optical communication system utilizing a sparse nonlinear equalizer with a variable step size generalized orthogonal matching pursuit

Yizhan Dai, Xiao Chen, Xingqi Yang, Zhijian Tong, Zihao Du, Weichao Lyu, Chao Zhang, Hao Zhang, Haiwu Zou, Yongxin Cheng, Dongfang Ma, Jian Zhao, Zejun Zhang, and Jing Xu
Opt. Express 29(20) 32228-32243 (2021)

90-m/560-Mbps underwater wireless optical communication utilizing subband multiple-mode full permutation CAP combined with an SNR-weighted detector and multi-channel DFE

Wenmin Ge, Zihao Du, Chengye Cai, Guangbin Song, Sitong Qin, Haipeng Wang, Tianhao Zhang, and Jing Xu
Opt. Express 31(8) 13154-13168 (2023)

Underwater wireless optical communication utilizing low-complexity sparse pruned-term-based nonlinear decision-feedback equalization

Chao Fei, Ruilin Chen, Ji Du, Yuan Wang, Jiahan Tian, Guowu Zhang, Junwei Zhang, Xiaojian Hong, and Sailing He
Appl. Opt. 61(22) 6534-6543 (2022)

56-m/3.31-Gbps underwater wireless optical communication employing Nyquist single carrier frequency domain equalization with noise prediction

Xiao Chen, Weichao Lyu, Zejun Zhang, Jian Zhao, and Jing Xu
Opt. Express 28(16) 23784-23795 (2020)

100 m/500 Mbps underwater optical wireless communication using an NRZ-OOK modulated 520 nm laser diode

Jiemei Wang, Chunhui Lu, Shangbin Li, and Zhengyuan Xu
Opt. Express 27(9) 12171-12181 (2019)