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Yayın Channel modelling for indoor visible light communications(Royal Society Publishing, 2020-04-17) Miramirkhani, Farshad; Uysal, MuratVisible light communication (VLC) allows the dual use of light-emitting diodes (LEDs) for wireless communication purposes in addition to their primary purpose of illumination. As in any other communication system, realistic channel modelling is a key for VLC system design, analysis and testing. In this paper, we present a comprehensive survey of indoor VLC channel models. In order to set the background, we start with an overview of infrared (IR) channel modelling, which has received much attention in the past, and highlight the differences between visible and IR optical bands. In the light of these, we present a comparative discussion of existing VLC channel modelling studies and point out the relevant advantages and disadvantages. Then, we provide a detailed description of a site-specific channel modelling approach based on non-sequential ray tracing that precisely captures the optical propagation characteristics of a given indoor environment. We further present channel models for representative deployment scenarios developed through this approach that were adopted by the Institute of Electrical and Electronics Engineering (IEEE) as reference channel models. Finally, we consider mobile VLC scenarios and investigate the effect of receiver location and rotation for a mobile indoor user. This article is part of the theme issue ‘Optical wireless communication’.Yayın Channel modeling and characterization for VLC-based medical body sensor networks: trends and challenges(IEEE, 2021-11-15) Dönmez, Barış; Mitra, Rangeet; Miramirkhani, FarshadOptical Wireless Communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers, i.e., visible, Infrared (IR), and Ultraviolet (UV) bands. In this paper, we focus on indoor Visible Light Communication (VLC)-based Medical Body Sensor Networks (MBSNs) which allow the Light Emitting Diodes (LEDs) to communicate between on-body sensors/subdermal implants and on-body central hubs/monitoring devices while also serving as a luminaire. Since the Quality-of-Service (QoS) of the communication systems depends heavily on realistic channel modeling and characterization, this paper aims at presenting an up-to-date survey of works on channel modeling activities for MBSNs. The first part reviews existing IR-based MBSNs channel models based on which VLC channel models are derived. The second part of this review provides details on existing VLC-based MBSNs channel models according to the mobility of the MBSNs on the patient’s body. We also present a realistic channel modeling approach called site-specific ray tracing that considers the skin tissue for the MBSNs channel modeling for realistic hospital scenarios.Yayın Reordering of polystyrene gel due to multiple swelling in organic vapor fast transient fluorescence technique study(Elsevier Science SA, 2006-07-31) Erdoğan, Matem; Pekcan, Mehmet ÖnderReordering of disc-shaped polystyrene (PS) gels due to multiple swelling, under organic vapor was studied by using Fast Transient Fluorescence (FTRF) technique. Disc-sbaped polystyrene gels were prepared by free radical copolymerization (FRC) of styrene (S) with ethylene glycol dimethacrylate (EGDM) as a crosslinker. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P doped PS gels under chloroform vapor. After each swelling step, gels were left to dry in an oven at 30 degrees C for consecutive reswelling experiments. Decay curves of P were measured and pyrene lifetimes, tau, were determined. It was observed that tau values decreased as swelling recycles were repeated. It was observed that after the fifth swelling step, two different regimes appeared in the swelling processes in PS gels. Swelling time constant, tau(c), and cooperative diffusion coefficients, D-c were determined by using Li-Tanaka equation for each swelling step in both regimes. It was observed that D-c values decreased up to tenth swelling step and then remained unchanged in both regimes.
