Low-Complexity Digital Equalizers for High-Speed Underwater Optical Wireless Communication

Hundreds of Megabit per second (Mb/s) data transmission over a moderate range (10m) underwater optical wireless channel is implemented with 4-level pulse amplitude modulation scheme using an off-the-shelf light-emitting diode as the optical source and digital equalizers. In particular, the channel nonlinear distortion from light-emitting diode is considered and a matched model is developed. To mitigate these distortions under various 4-level pulse amplitude modulation signal baud rates, the Bit error rate (BER) and Signal-to-noise ratio (SNR) performances of the pre-, post- and matchedequalizers are evaluated and compared. The digital matched-equalizer bank is shown and verified to offer the best BER/SNR performance for 4-level pulse amplitude modulation signal using more than 200 MBaud rate. With the proposed equalizer, we have recorded the highest data rate of 600Mb/s at 20% FEC limit over 10m free-space underwater link.