Design And Performance Improvement of an Underwater Visible Light Communication System Using Pam-4 and Adaptive Equalization

Abstract

Acoustic and radio-frequency links are the traditional choices for underwater communication, but both have real drawbacks: acoustic links are slow, and RF is absorbed almost immediately in water. Underwater optical wireless communication (UOWC) avoids both problems over short distances by carrying data on visible light. Most high-speed UOWC systems rely on FPGAs, laser diodes, or specialised hardware; this work instead builds and tests a link from low-cost, off-the-shelf parts: an Arduino transmitter and a Raspberry Pi receiver. A baseline On-Off Keying (OOK) link was built and tested first, reaching 5.33 Mbps. Once that baseline worked, the same hardware was reconfigured for 4-level Pulse Amplitude Modulation (PAM-4) with a small digital FIR equalizer at the receiver to counteract the channel’s low-pass behaviour. The equalized PAM-4 link reached 10.1–10.2 Mbps and decoded an extended test message with zero bit errors at an estimated SNR of 28.77 dB. Signal traces before and after equalization show the effect directly: the four PAM-4 levels overlap heavily without correction and separate into clean steps once equalized. The results show a low-cost, commodity-hardware UOWC link can gain substantial throughput and reliability by upgrading the modulation format and adding a lightweight equalizer, without changing the underlying electronics.