<p>An optical indoor positioning system using an optical receiver and camera is proposed. Compared with previous works in this field, our system improved the coverage without sacrificing accuracy. Thus, the proposed indoor positioning system is more suitable under environments with dense obstacles, such as warehouses, hospitals, and factories. Since the camera is deployed at the receiver side, the angle of arrival (AoA) can be estimated by recognizing the light source in an image. The optical receiver is able to measure received signal strength (RSS). Combining the information in AoA and RSS, the relative position of the receiver to the light source can be estimated. In this system, the position of the light source can be sent to the receiver applying visible light communication. Thus, both communication and positioning can be enabled using a single light-emitting diode on the transmitter side.</p>
The ocean surface has considerable impact on air-to-sea (or sea-to-air) imaging, lidar scanning, and optical communication. This surface is rarely smooth, of course, especially in the littoral region (due to a variety of impacts, from wind to ship wakes, etc.). Most current and previous methods for addressing this roughness and its impact on optical propagation are either fully statistical, totally theoretical, or are “mixed methods” based on a combination of statistical models and parametric-based physical models (our preferred approach). To better understand the statistical nature of the sea surface, experiments were performed in a 50 foot long wave tank capable of not only producing large scale, multi-frequency waves, but also wind driven waves over a range of velocities. High speed imaging (i.e., Photron FASTCAM Mini series<sup>(R)</sup>) of laser beam projection as well as spatial distribution of surface glint, scanned laser velocimetry measurements of the surface, and deflection statistics of the doubled Nd:YAG (532 nm) beam will all be utilized to produce statistical models of sea surface perturbations under various wind loads and larger scale wave forcing. These data, combined with our mixed model, will help us to measure, analyze, and understand the shape of the sea surface and assess its subsequent impact on optical propagation and specifically on aerial to underwater FSO communication links.
Proc. SPIE. 10770, Laser Communication and Propagation through the Atmosphere and Oceans VII
KEYWORDS: Turbulence, Ocean optics, Atmospheric propagation, Adaptive optics, Global system for mobile communications, Signal to noise ratio, Water, Laser beam propagation, Scintillation, Wave propagation
Reliable communication between aerial and undersea vehicles is a challenging issue because radio frequency signals are attenuated drastically in sea water while acoustic waves are not preferable in terrestrial links. Located in the transmittance windows of both sea water and the atmosphere, blue-green laser based free-space optical communication systems are capable of providing high speed, low latency data links for this very scenario. Apart from the absorbing and scattering attenuations in the air-water channel, another limiting factor impacting efficient laser beam propagation is the turbulence induced intensity fluctuations. Pure attenuation in sea water restricts the laser communication distance to ~100 meters, which will further reduce to ~10 meters in the presence of oceanic turbulence. Meanwhile, atmospheric turbulence can also substantially degrade the beam quality if the aerial vehicle is at high altitude. In this study, we focus our effort on the turbulence effects on beam propagation in the air-water two-stage links, not taking into account media attenuation or water surface distortions. Considering the complexity of the depth dependence of salinity and temperature in sea water and the altitude dependence of air refractive-index structure constant, we use numerical methods to simulate the beam propagation through the two-stage turbulence channel, which is modeled by discrete phase screens generated with parameterized atmospheric and oceanic turbulence power spectrums. On that basis, beam spread, area scintillation and SNR penalty at the receiver end are analyzed for the uplink as well as the downlink transmission.
In this study, a special class of nonuniformly correlated beams with radially symmetric coherence distributions, called
radial partially coherent beams (RPCBs), is numerically studied. By spatially modulating uniformly correlated phase
screens used for generating conventional Gaussian Schell-model beams, RPCBs with arbitrary distributions of degree of
coherence are produced. RPCBs whose degree of coherence decreases from the beam center along the radial direction
were found to self-focus in free-space propagation, leading to augmented optical intensity near the beam center.
Meanwhile, the scintillation mitigation ability of RPCBs remains significant. By means of wave optics simulation,
propagation properties of RPCBs in anisotropic non-Kolmogorov turbulence are analyzed. Simulation results show that,
under certain conditions RPCBs are still able to deliver improved performance in anisotropic non-Kolmogorov
turbulence. Moreover, due to the elliptical far-field irradiance pattern caused by anisotropy, a matched elliptic receiving
aperture can further reduce the turbulence-induced scintillation.