Spectral efficient and high data rate ring topology based UWOC system with carrier-free optical add-drop nodes

Area of Science:

• Underwater Wireless Optical Communication (UWOC)
• Optical Networking
• Data Transmission Technologies

Background:

• Underwater communication faces challenges from turbulence and limited connectivity.
• Existing systems often lack spectral efficiency and high data rates for demanding applications.
• The Internet of Underwater Things (IoUT) requires robust and high-performance communication solutions.

Purpose of the Study:

• To design and evaluate a spectral-efficient, high-data-rate UWOC system using a ring topology.
• To enable full-duplex data transmission between multiple optical add-drop nodes (OADNs).
• To assess system resilience against underwater bubbling-induced turbulence and node failures.

Main Methods:

• A ring topology UWOC system was designed for full-duplex data transmission at 20 Gb/s per node.
• Quadrature Phase Shift Keying (QPSK) for downlink (DL) and On-Off Keying (OOK) for uplink (UL) were employed.
• A pulse carver based on a dual-drive Mach-Zehnder modulator (DD-MZM) facilitated full-duplex transmission.
• The Gamma-Gamma channel model simulated underwater bubbling turbulence.
• Bit-error rate (BER) was analyzed for DL and UL channels under varying bubble rates.

Main Results:

• The system achieved the target forward-error correction (FEC) BER limit of 3.8 × 10⁻³ for both DL and UL channels.
• Performance remained within acceptable limits across different underwater bubble generation rates.
• The system demonstrated robustness, sustaining 80% node connectivity during single OADN failure and 100% during primary link failure.

Conclusions:

• The proposed ring topology UWOC system is spectral-efficient, high-data-rate, and capable of full-duplex communication.
• The system exhibits significant resilience to underwater channel impairments and network failures.
• This UWOC solution is a promising candidate for future high-speed, long-range Internet of Underwater Things (IoUT) applications.