ABSTRACT
The widespread use of light-emitting diodes (LEDs) and cameras in vehicular environments provides an excellent opportunity for optical camera communication (OCC) in intelligent transport systems. OCC is a promising candidate for the Internet of Vehicles (IoV), and it uses LEDs as the transmitter and cameras as the receiver. However, the mobility of vehicles has a significant detrimental impact on the OCC system's performance in vehicular environments. In this paper, a traffic light that uses multiple-input multiple-output (MIMO) technology serves as the transmitter, and the receiver is a camera mounted on a moving vehicle. The impact of vehicle mobility on the vehicular MIMO-OCC system in the transportation environment is then examined using precise point spread function (PSF) analysis. The experimental results are used to evaluate the proposed PSF. A good agreement between the laboratory's recorded videos and this PSF model's simulations is observed. Moreover, the signal-to-noise ratio (SNR) and signal-to-interference-plus-noise ratio (SINR) values are evaluated. It is shown that they are greatly influenced by the vehicle's speed, direction of motion, and position of the camera. However, since the angular velocity in a typical transportation environment is low, it does not have a significant impact on the performance of the vehicular OCC systems.
ABSTRACT
Due to its spatial modulation feature and potential applications, optical camera communication (OCC) has gained significant attention in recent years for a range of applications including underwater. Nonetheless, due to the low frame rates of the camera, the OCC data rate is rather low, which is why multiple-input-multiple-output (MIMO) has been adopted to compensate. In MIMO systems, however, the signal from one light emitting diode (LED) may result in interference on the image sensor (i.e., the camera) resulting in inter-pixel interference (IPI). This paper presents a comprehensive model of the underwater OCC (UOCC) and experimentally verifies its performance under IPI by comparing signal to interference and noise ratio (SINR). The effect of distance between LEDs according to LED diameter D on signal to interference ratio (SIR) is presented and results indicate that coastal water has the SIR gain â¼2.5â dB for the link span of 1 to 6 m, and for harbor water channel length from 0.4 to 1.4 m the gain increased from â¼2 to â¼5â dB for d of 2D compared with d of 0.5D.
ABSTRACT
Corrections are given for errors in the presentation of equations in J. Opt. Soc. Am. A34, 1187 (2017)JOAOD60740-323210.1364/JOSAA.34.001187.
ABSTRACT
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 effect of turbulence on the UOWC system 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 water to obtain the PDF. Results show that lognormal distribution closely matches the measured PDF for a range of link spans. In UOWC systems, the link span is one of the main factors influencing fluctuations of the received optical power, and it has not been thoroughly investigated. In this work, the scintillation index and turbulence-induced power loss are obtained for a range of turbulence strengths and transmission link spans. Finally, we show that there is a good agreement between the experimental and simulated results.
ABSTRACT
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.
ABSTRACT
In recent years, interest in medical application of lasers especially as a surgical alternative is considerably increasing due to their distinct advantages such as non-contact intervention, bacteriostasis, less traumatization, minimal invasiveness, decreased bleeding and less heat damage. The present study aimed to evaluate the temperature changes and the consequent released thermal stress in cortical bone caused by an Erbium:yttrium aluminum garnet (Er:YAG) laser (Fideliss 320A, Fotona Inc., Deggingen, Germany) during osteotomy, using mathematical computation by means of Maple software, version 9.5 (Maplesoft, a division of Waterloo Maple Inc., Canada). The results obtained here were compared with the experimental measurements using Er:YAG laser in the osteotomy clinics. A bone slab with thickness of 1 mm was simulated in Maple software. Then, an Er:YAG laser emitting 100 µs pulses at a wavelength of 2940 nm were modeled. Two different clinical settings of the Er:YAG laser with 200 mJ and 400 mJ energies, both with 100 µs exposure and 500 µs silence were studied. To investigate the temperature distribution in the cortical bone, the time-dependent heat conduction equations were defined and solved in the Maple software. Finally, by defining the heat distribution function in the Maple, thermal stress in the bone was investigated. Results of the computations showed that, on the bone irradiated area (center of the bone surface) the maximum temperature rise was 0.8°C and 1.6°C, for 200 mJ and 400 mJ Er:YAG laser exposure, respectively. The temperature rise reached to its minimum at radial distances of 1.2 cm from the point of irradiated area for 200 mJ laser while it was 1.5 cm for 400 mJ laser. For 200 mJ laser the maximum derived radial (σ rr ), axial (σ zz ) and azimuthally (σ θθ ) stress components were 0.20, 0.16 and 0.08 MPa, respectively. While, for 400 mJ laser the maximum derived σ rr , σ zz and σ θθ stress components were 0.39, 0.31 and 0.16 MPa, respectively. These results confirm that use of 100 µs Er:YAG laser pulses with 500 µs silence at 200 and 400 mJ energies minimizes thermal tissue damage for the laser osteotomies, without continued water cooling (irrigation) on the exposed area.
ABSTRACT
In this paper a hybrid modulation scheme based on pulse position modulation (PPM) and binary phase shift keying subcarrier intensity modulation (BPSK-SIM) schemes for free-space optical communications is proposed. The analytical bit error rate (BER) performance is investigated in weak and saturated turbulence channels and results are verified with the simulation data. Results show that performance of PPM-BPSK-SIM is superior to BPSK-SIM in all turbulence regimes; however, it outperforms 2-PPM for the turbulence variance σ(1)(2)>0.2. PPM-BPSK-SIM offers a signal-to-noise ratio (SNR) gain of 50 dB in the saturation regime compared to BPSK at a BER of 10(-6). The SNR gain in comparison to PPM improves as the strength of the turbulence level increases.
