Effect of Link Misalignment in the Optical-Internet of Underwater Things

Abstract

Underwater wireless optical communication (UWOC) enables high-speed links in water for the optical Internet of Underwater Things (O-IoUT) networks. O-IoUT provides various marine applications, including ocean exploration, environmental monitoring, and underwater navigation. O-IoUT typically utilizes light-emitting diodes (LEDs) and different laser diodes (LDs) such as green/blue lasers to achieve efficient data communication in the underwater environment.The high-speed optical communication is limited up to a few tens of meters due to underwater channel impairments and misalignment between the transmitter (Tx) and the receiver (Rx). UWOC provides high-speed communications only in the line of sight conditions, and a small misalignment between the Tx and the Rx can degrade the system performance. In an attempt to understand and minimize this misalignment issue, we investigate how received power in a UWOC system depends on the transmitted beam's divergence angle. Simulation results are provided to show the effectiveness of the study by comparing the plane, Gaussian, and spherical beams. Monte Carlo simulations are utilized to determine the maximum allowable lateral offset between Tx and Rx for a given Tx divergence angle. The results provide an overview and design-based trade-off between different parameters such as lateral offset, the power received, and bandwidth of the channel. The proposed method improves not only the maximum allowed link-span but also the bandwidth of the channel for a given transmission distance.

Performance Analysis and Design Considerations of the Shallow Underwater Optical Wireless Communication System with Solar Noises Utilizing a Photon Tracing-Based Simulation Platform

“…The propagation distance between two interaction events is defined as step size ∆s with its probability distribution function (PDF) based on the Beer Law: p(∆s) = c(λ)e −c(λ)∆s , then ∆s can be simplified and randomly chosen as ∆s = −InR 5 /c(λ), in which R 5 represents another RV, c(λ) is the water attenuation coefficient. As shown in Figure 3, the weight of photon after each interaction is used to update as W n+1 = W n α n+1 0 , where α 0 = b(λ)/c(λ) [23]. The new direction is described by the scattering polar angle θ s , which can be derived using the Henyey Greenstein scattering phase functions (HG-SPF), ξ(θ s , φ s ) [24].…”

Storage Capabilities in Underwater Wireless Sensor Networks for Energy Balancing and Channel Alignment

“…The estimation is done posterior to calculations of data transfer where relationship which influence the fluctuations such as channel response, back off time are not considered and only statistical characteristics are alone inferred. In [8] discussion on the influence of misalignment with optical communication has been studied considered beam divergence in transmitter. The maximum allowable offset calculation has also been done in varying in underwater channel via simulations to validate the bandwidth and its corresponding distance of transmission.…”

Parameter Optimization for an Underwater Optical Wireless Vertical Link Subject to Link Misalignments

“…For instance, [23] presented a theoretical and experimental study of the effect of displacement in the Rx position and the inclination angle with respect to the main optical axis on the detected signal. The effect of beam divergence angle on the received power was investigated in [24], taking into consideration the Tx-Rx lateral offset. Also, for the case of turbid waters, [25] studied the effect of Rx angular misalignments and its field-of-view (FoV) on the received signal.…”