Joint SIC and power allocation for a multi-user paired UWOC-NOMA system in a turbulence environment.

This paper proposes a staircase joint optimization scheme (SJOS) with alternating diagonal interference cancellation and power allocation in an underwater wireless optical communication system based on nonorthogonal multiple access (UWOC-NOMA) with the multi-user paired. The scheme employs the directional iteration to alternatively optimize the subproblems of the interference cancellation and the power allocation. Furthermore, a one-way sorting algorithm based on the alternating diagonal interference cancellation and power allocation subalgorithm based on the conjugate gradient method are presented to solve the two subproblems, respectively. Simulation results show that the algorithm effectively reduces the average outage probability of the system with fast convergence, even with an increase in the number of paired users.

Modeling and performance analysis of underwater wireless optical absorption, scattering, and turbulence channels employing Monte Carlo-multiple phase screens.

The absorption, scattering, and turbulence effects have a significant impact on the performance of underwater wireless optical communication (UWOC). Therefore, it is crucial to consider seawater's optical parameters comprehensively when designing UWOC systems. So far, most studies on the UWOC channel have separately modeled the absorption and scattering, and turbulence of seawater, and furthermore, the continuous phase perturbations caused by turbulence are neglected to simplify the model when modeling turbulence channels. Hence, this paper simultaneously considers the absorption, scattering, and turbulence effects of seawater and proposes a UWOC channel modeling method that combines Monte Carlo simulation with multiple phase screen approaches. Subsequently, the impacts of different systems and channel conditions on system performance are explored, and simulation results indicate that as the turbidities and turbulence intensities of the seawater increase, the probability density function of received light signal intensity becomes more dispersed. The turbulence introduces an increase in path loss of approximately 5 dB compared to its absence. Furthermore, the channel impulse response (CIR) is obtained, where the turbulence effects cause a 50% decrease in the CIR peak and the noticeable temporal spread.

Modeling and performance analysis of oblique underwater optical communication links considering turbulence effects based on seawater depth layering.

Underwater wireless optical communication (UWOC) has been introduced to support emerging high-speed and low latency underwater communication applications. Most of the current studies on UWOC assume that the water temperature and salinity are constant, which can be justified only for horizontal links. In fact, as the temperature and salinity of seawater change with increasing depth, the seawater at different depths is bound to exhibit different optical properties. This implies that for the same link length, the communication system with the transmitter and receiver at different depths, will exhibit different performances. This paper first proposes an oblique optical link model considering turbulence effects, which is based on the layering of temperature and salinity with depth in realistic ocean water. Subsequently, the performance of the optical communication system with vertical and oblique links is analysed by adopting the oceanic power spectrum and seawater data from different ocean areas measured by the global ocean observation buoy, Argo. Our simulation shows that the performance of the underwater optical communication system is worse when the optical transmitter is located at the mixed layer than at the thermocline. When the transmitter is at the thermocline, the communication quality of the system will be worse at environments that temperature and salinity vary more slowly. When the tilt angle of the optical link in the vertical direction is less than 10°, the oblique link can be treated as a vertical link with the same link length.