Underwater Optical Wireless Communications, Networking, and Localization: A Survey (1803.02442v1)

Abstract: Underwater wireless communications can be carried out through acoustic, radio frequency (RF), and optical waves. Compared to its bandwidth limited acoustic and RF counterparts, underwater optical wireless communications (UOWCs) can support higher data rates at low latency levels. However, severe aquatic channel conditions (e.g., absorption, scattering, turbulence, etc.) pose great challenges for UOWCs and significantly reduce the attainable communication ranges, which necessitates efficient networking and localization solutions. Therefore, we provide a comprehensive survey on the challenges, advances, and prospects of underwater optical wireless networks (UOWNs) from a layer by layer perspective which includes: 1) Potential network architectures; 2) Physical layer issues including propagation characteristics, channel modeling, and modulation techniques 3) Data link layer problems covering link configurations, link budgets, performance metrics, and multiple access schemes; 4) Network layer topics containing relaying techniques and potential routing algorithms; 5) Transport layer subjects such as connectivity, reliability, flow and congestion control; 6) Application layer goals and state-of-the-art UOWN applications, and 7) Localization and its impacts on UOWN layers. Finally, we outline the open research challenges and point out the future directions for underwater optical wireless communications, networking, and localization research.

• The paper presents a comprehensive layered analysis of underwater optical wireless networks, outlining network architectures and addressing critical physical and data link challenges.
• The paper employs advanced modeling techniques such as the Beer-Lambert law, radiative transfer equations, and Monte Carlo simulations to characterize absorption, scattering, and turbulence effects.
• The paper identifies key future research directions including hybrid system integration, cross-layer optimization, and innovative localization strategies to bridge theory with real-world applications.

Survey on Underwater Optical Wireless Communications, Networking, and Localization

Underwater Optical Wireless Communications (UOWCs) represent a significant advancement over traditional acoustic and radio frequency (RF) communications in underwater environments, offering potential for supporting high-speed data transmissions with low latency. The survey conducted by Saeed et al., titled "Underwater Optical Wireless Communications, Networking, and Localization: A Survey," provides a thorough examination of the challenges, developments, and prospects of UOWCs through a comprehensive layer-by-layer investigation of Underwater Optical Wireless Networks (UOWNs).

Layered Analysis of UOWNs

1. Network Architectures

The authors delineate potential network architectures for UOWNs which can operate in both ad hoc and infrastructure-based modes. Ad hoc networks capitalize on dynamic routing without pre-installed infrastructure, whereas infrastructure-based networks rely on Optical Access Points (OAPs) or Optical Base Stations (OBSs), forming localized wireless networks. This approach underlines the importance of novel architectural designs given the UOWC's directional light propagation and limited range.

2. Physical Layer Challenges

The survey underscores the pivotal physical layer considerations, addressing underwater optical propagation characteristics—such as absorption, scattering, and turbulence. Detailed attention is given to the significance of choosing optimal wavelengths, particularly within the 450-550 nm range (blue and green light), which features reduced attenuation. This section highlights modeling methodologies for UOWC channels, including Beer-Lambert law, radiative transfer equation, and Monte Carlo simulations.

3. Data Link Layer: Link Configuration and Access

Saeed et al. detail various UOWC link configurations, such as Line-of-Sight (LoS), Non-Line-of-Sight (NLoS), and Retro-Reflective Links, pertinent for managing the trade-off between communication range and coverage span. Furthermore, they explore multiple access schemes, including TDMA, FDMA, CDMA, and explore the prospects of NOMA and WDMA, pivotal for improving network throughput and spectral efficiency.

4. Network Layer: Routing Protocols

The authors discuss relaying and routing protocols necessary for extending communication range and enhancing network connectivity in UOWNs. Protocols such as location-based routing and cross-layer design strategies are noted for their potential to enhance packet delivery given the inherent short-range communication limitations of UOWC.

5. Transport Layer Considerations

They address issues related to transport layer, such as connectivity, reliability, and flow control, emphasizing the necessity of innovative protocols responsive to challenges posed by the underwater environment's dynamic and limited connectivity scenarios.

6. Applications and Localization

This section articulates applications of UOWNs ranging from environmental monitoring and ocean sampling to military surveillance. The discussion extends to localization strategies essential for effective operation in UOWNs, emphasizing the unsuitability of traditional GPS and bringing new focus to optical-based localization approaches.

Open Challenges and Future Directions

The survey concludes by outlining open research challenges and potential future avenues. Notably, these include the need for more robust channel models, the integration of cross-layer designs, innovative energy harvesting solutions, and practical implementations that bridge the existing gap between theory and real-world applications.

In envisioning the future of UOWNs, the paper advocates for continued research in hybrid systems that combine different carrier waves and in the burgeoning field of the Internet of Underwater Things (IoUTs), leveraging UOWCs for improved connectivity and system performance underwater.

This survey serves as a comprehensive guide for continued research and development in the field of UOWCs, providing valuable insights for experienced researchers working toward advancing underwater networking capabilities.