Demonstration of a Real-time UWOC System Using a Bandwidth Limited LED Based on Hardware and Software Equalization

In this work, we propose and experimentally demon-strate a real-time and cost-efficient underwater wireless optical communication (UWOC) system based on field programmable gate arrays (FPGAs) for practical application. A three-stage cascaded T-bridge equalizer (TCBE) is designed to enlarge 3 dB bandwidth of the light-emitting diode (LED). Also, a digital waveform shaping filter (DWSF) is proposed to assist the TCBE circuit by shortening the rise and fall time of the received waveform and adjusting equalization parameters to flexibly satisfy diverse communication scenarios. The 3 dB bandwidth of UWOC system is extended from 2.5 MHz to 44 MHz via TCBE. With the proposed scheme, a data rate of at least 50 Mbps with a bit error rate (BER) of ${8} \times {10}^{{-5}}$ without forward error correction (FEC) code can be guaranteed over an underwater channel of 1 m. On the basis of TCBE, the DWSF is capable of further reducing the BER by 15%, 22%, 26%, 28%, 95%, and 98% for the data rates of 10 Mbps, 20 Mbps, 30 Mbps, 40 Mbps, 45 Mbps, and 50 Mbps, respectively. The results show that the method can remarkably improve the performance of UWOC system, especially when data rates are greater than 40 Mbps.