Turbulence affects the performance of underwater wireless optical communications (UWOC). Although multiple scattering and absorption have been previously investigated by means of physical simulation models, still a physical simulation model is needed for UWOC with turbulence. In this paper, we propose a Monte Carlo simulation model for UWOC in turbulent oceanic clear water, which is far less computationally intensive than approaches based on computational fluid dynamics. The model is based on the variation of refractive index in a horizontal link. Results show that the proposed simulation model correctly reproduces lognormal probability density function of the received intensity for weak and moderate turbulence regimes. Results presented match well with experimental data reported for weak turbulence. Furthermore, scintillation index and turbulence-induced power loss versus link span are exhibited for different refractive index variations.

In advanced driver assistance systems to conditional automation systems, monitoring of driver state is vital for predicting the driver's capacity to supervise or maneuver the vehicle in cases of unexpected road events and to facilitate better in-car services. The paper presents a technique that exploits millimeter-wave Doppler radar for 3D head tracking. Identifying the bistatic and monostatic geometry for antennas to detect rotational vs. translational movements, the authors propose the biscattering angle for computing a distinctive feature set to isolate dynamic movements via class memberships. Through data reduction and joint time-frequency analysis, movement boundaries are marked for creation of a simplified, uncorrelated, and highly separable feature set. The authors report movement-prediction accuracy of 92%. This non-invasive and simplified head tracking has the potential to enhance monitoring of driver state in autonomous vehicles and aid intelligent car assistants in guaranteeing seamless and safe journeys.

Underwater optical wireless communications (UOWC) performance is affected by turbulence. However, not much research has been carried out to estimate the probability density function (PDF) of the received optical power. In this paper, we investigate the turbulence effect on UOWC using a new experimental setup with a variable link span in a water pool. Different turbulence levels are created by changing the temperature and the rate of an injected water flow in the pool in order to obtain the PDF. Results show that lognormal distribution fits well with the measured PDF up to the scintillation index value of 0.07. In UOWC systems the link span is one of the main factor influencing fluctuations of the received optical power, which has not been investigated. In this work, we obtain the scintillation index and turbulence induced power loss for a range of turbulence strengths and for a transmission link span of up to 12 m. Finally, we show that there is a good agreement between the experimental and simulated results.

In underwater optical wireless communications (UOWC) the link performance is greatly affected by the turbulence. Turbulence is due to the random variations of the refractive index of water, which leads to both intensity (i.e., fading) and phase fluctuation of the optical beam. The effects of turbulence on link performance depend on the choice of system parameters. In this paper, the effects of the transmission link span, divergence angle of the transmitted Gaussian beam, receiver's (Rx) aperture diameter and field of view (FOV) on the UOWC link performance under the turbulence condition is investigated. The results show that, lognormal and negative exponential distributions fit well with the probability density function of the received light intensity under weak-to-strong and saturated turbulence regimes or for a link span longer than 120 m. The goodness of fit test is performed to validate the conformity of the two distributions with the simulation results. The scintillation index (SI) variation as a function of the four mentioned parameters under different turbulence regimes is investigated. It is shown that, for a 100 m link span and under weak turbulence, while the effect of transmitter's FOV on SI is negligible, increasing the transmitter's divergence angle by 1.72º and decreasing the Rx's aperture diameter by 9.2 cm, increases the SI by 53 times and 77 times, respectively.