Heterogeneous integration of optical wireless communications within next generation networks

Unprecedented traffic growth is expected in future wireless networks and new technologies will be needed to satisfy demand. Optical wireless (OW) communication offers vast unused spectrum and high area spectral efficiency. In this work, optical cells are envisioned as supplementary access points within heterogeneous RF/OW networks. These networks opportunistically offload traffic to optical cells while utilizing the RF cell for highly mobile devices and devices that lack a reliable OW connection. Visible light communication (VLC) is considered as a potential OW technology due to the increasing adoption of solid state lighting for indoor illumination. Results of this work focus on a full system view of RF/OW HetNets with three primary areas of analysis. First, the need for network densication beyond current RF small cell implementations is evaluated. A media independent model is developed and results are presented that provide motivation for the adoption of hyper dense small cells as complementary components within multi-tier networks. Next, the relationships between RF and OW constraints and link characterization parameters are evaluated in order to define methods for fair comparison when user-centric channel selection criteria are used. RF and OW noise and interference characterization techniques are compared and common OW characterization models are demonstrated to show errors in excess of 100x when dominant interferers are present. Finally, dynamic characteristics of hyper dense OW networks are investigated in order to optimize traffic distribution from a network-centric perspective. A Kalman Filter model is presented to predict device motion for improved channel selection and a novel OW range expansion technique is presented that dynamically alters coverage regions of OW cells by 50%. In addition to analytical results, the dissertation describes two tools that have been created for evaluation of RF/OW HetNets. A communication and lighting simulation toolkit has been developed for modeling and evaluation of environments with VLC-enabled luminaires. The toolkit enhances an iterative site based impulse response simulator model to utilize GPU acceleration and achieves 10x speedup over the previous model. A software defined testbed for OW has also been proposed and applied. The testbed implements a VLC link and a heterogeneous RF/VLC connection that demonstrates the RF/OW HetNet concept as proof of concept

Interference mitigation through user association and receiver field of view optimization in a multi-user indoor hybrid RF/VLC illuminance-constrained network

In this paper we address interference mitigation through user association and receiver field of view (FOV) optimization in a multi-user indoor optical wireless communication (OWC) scenario. We explore several dynamic FOV receiver solutions including steerable (SDFOV) and non-steerable (DFOV) to optimize performance for multiple devices experiencing orientation dynamics. We compare their performance to a baseline fixed FOV receiver (FFOV). Through modeling and simulation we find that SDFOV receivers outperform DFOV by up to 2.6x and FFOV by up to 5.6x in terms of average minimum throughput gain using our test scenario. Similarly, DFOV receivers can achieve up to 2.2x gain over FFOV receivers. For multi-user environments, we compare the performance of coordinated versus distributed system control. Results show that in the worst case, the distributed greedy system performs on average 46%, 16%, and 57% below the coordinated system for SDFOV, DFOV, and FFOV, respectively at a reduced computational complexity compared to the centralized system. We also note that the performance gap in each system diminishes with increasing transmitter Lambertian order. This analysis is done under different room coverage achieved through optimizing the transmitted power to jointly maximize the minimum received power and the standard illuminance range probability at the working plane. Next, we show the impact of self- and random-human blockage at different Lambertian orders on the minimum and average user throughput values. Lastly, we show the gains from employing the hybrid RF/VLC network compared to a VLC-only mode for two different strategies: (1) minimum-throughput-enhancing and (2) sum-throughput-enhancing.https://ieeexplore.ieee.org/abstract/document/9300130Published versio

Identification of Small-Molecule Inhibitors of Neutral Ceramidase (nCDase) via Target-Based High-Throughput Screening

There is interest in developing inhibitors of human neutral ceramidase (nCDase) because this enzyme plays a critical role in colon cancer. There are currently no potent or clinically effective inhibitors for nCDase reported to date, so we adapted a fluorescence-based enzyme activity method to a high-throughput screening format. We opted to use an assay whereby nCDase hydrolyzes the substrate RBM 14-16, and the addition of NaIO4 acts as an oxidant that releases umbelliferone, resulting in a fluorescent signal. As designed, test compounds that act as ceramidase inhibitors will prevent the hydrolysis of RBM 14-16, thereby decreasing fluorescence. This assay uses a 1536-well plate format with excitation in the blue spectrum of light energy, which could be a liability, so we incorporated a counterscreen that allows for rapid selection against fluorescence artifacts to minimize false-positive hits. The high-throughput screen of >650,000 small molecules found several lead series of hits. Multiple rounds of chemical optimization ensued with improved potency in terms of IC50 and selectivity over counterscreen assays. This study describes the first large-scale high-throughput optical screening assay for nCDase inhibitors that has resulted in leads that are now being pursued in crystal docking studies and in vitro drug metabolism and pharmacokinetics (DMPK).National Cancer Institute https://doi.org/10.13039/100000054Stony Brook Cancer CenterPeer Reviewe

A hybrid radio frequency and broadcast visible light communication system

Abstract–Wireless network data consumption is experiencing drastic increases due to growing demands of mobile services and applications. Deployed networks using Radio Frequency (RF) communications are characterized by a shared medium, limited available spectrum and limited ability to scale with increasing demand. Directional communications, including Visible Light Communications (VLC), can limit contention in controlled environments and provide scalability through spatial reuse of the medium. This solution can provide massive aggregate data capacity in indoor scenarios if properly distributed. In this paper we propose an indoor hybrid system that integrates WiFi and VLC luminaries. Our system utilizes (i) broadcast VLC channels to supplement RF communications and (ii) a handover mechanism between WiFi and VLC to dynamically distribute resources and optimize system throughput. This approach offers the bandwidth density benefits of VLC, provides a non-intrusive RF back-channel, maintains compatibility with conventional RF devices, and demonstrates excellent scalability. Analytical and simulation results show improvements in aggregate performance (i.e., throughput and delay) of the hybrid, when compared to either system acting alone

Directional visible light communication signal enhancement using a varifocal micromirror with four degrees of freedom

We present the use of a micromirror to dynamically improve an optical wireless communiciations link. The signal-to-noise ratio (SNR) is improved by directing the output of a 675 nm laser diode modulated at 10 MHz toward a receiver and by varying the divergence of the output beam using a varifocal, tip-tilt-piston micromirror. The SNR has a dynamic range of 30 dB for a diffuse source, all by optimizing the overall shape and direction of the mirror

Directional visible light communication signal enhancement using a varifocal micromirror with four degrees of freedom

We present the use of a micromirror to dynamically improve an optical wireless communiciations link. The signal-to-noise ratio (SNR) is improved by directing the output of a 675 nm laser diode modulated at 10 MHz toward a receiver and by varying the divergence of the output beam using a varifocal, tip-tilt-piston micromirror. The SNR has a dynamic range of 30 dB for a diffuse source, all by optimizing the overall shape and direction of the mirror