Görünür ışık haberleşmesi için kanal modelleme ve nitelendirme: içmekan, araçsal ve sualtı kanallar

Despite the increasing attention on visible light communications (VLC) systems, there is a lack of proper visible light (VL) channel models. This is a serious concern since channel modeling is the very first step for efficient, reliable, and robust VLC system design. This dissertation focuses on channel modeling and characterization study for indoor, vehicular and underwater VLC. Our study is based on Zemax®; a commercial optical and illumination design software. Although the main purpose of such software is optical system design, we take advantage of the ray tracing features of this software which allows an accurate description of the interaction of rays emitted from the lighting source within a specified confined space. The simulation environment is created in Zemax® and enables us to specify the geometry of the environment, the objects within as well as the specifications of the sources (i.e., LEDs) and receivers (i.e., photodiodes). For a given number of rays and the number of reflections, the non-sequential ray tracing tool calculates the detected power and path lengths from source to detector for each ray. These are then imported to Matlab® and processed to yield the channel impulse response (CIR). In contrary to existing works which are mainly limited to ideal Lambertian sources and purely diffuse reflections, our approach is capable to obtain CIRs for any non-ideal sources as well as specular and mixed specular-diffuse reflections. Furthermore, we can precisely reflect the presence of objects and wavelength-dependent reflection characteristics of surface materials in channel study. In the first part of this thesis, we propose a realistic indoor channel modeling approach and carry out a detailed channel characterization study. We also investigate the effect of user mobility and receiver orientation on CIRs. In the second part of this thesis, we present VLC channel models for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) taking into account the asymmetrical pattern of headlamp and street lights, reflections from road surfaces and weather conditions. We further develop a closed-form path loss expression for V2V VLC channel for different weather conditions. In the last part of this thesis, we carry out a detailed underwater optical channel modeling and characterization study taking into account the reflection characteristics of the sea surface and sea bottom as well as the water characteristics, i.e., extinction coefficient, and scattering phase function of particles. We develop a closed-form path loss expression as an explicit function of water type, beam divergence angle and receiver aperture diameter and validate the accuracy of the proposed expression through Monte Carlo simulation results.