15 research outputs found
Communications and sensing of illumination contributions in a power led lighting system
Abstract — In recent years, LED technology emerged as a prime candidate for the future illumination light source, due to high energy efficiency and long life time. In addition, LEDs offer a superior flexibility in terms of colors and shapes, which leads to a potentially infinite variety of available light patterns. In order to create these patterns via easy user interaction, we need to sense the local light contribution of each LED. This measurement could be enabled through tagging of the light of each LED with unique embedded IDs. To this end, we propose a new modulation and multiple access scheme, named as codetime division multiple access- pulse position modulation (CTDMA-PPM): a form of PPM which is keyed according to a spreading sequence, and in which the duty cycle is subject to pulse width modulation (PWM) according to the required lighting setting. Our scheme considers illumination constraints in addition to the communication requirements and, to our best knowledge, it has not been addressed by other optical modulation methods. Based on the proposed modulation method and multiple access schemes, we develop a system structure, which includes illumination sources, a sensor receiver and a control system. Illumination sources illuminate the environment and transmit information, simultaneously. According to our theoretical analysis, this system structure could support a number of luminaries equal to the size of the CDMA codebook times the dimming range. I
The DarkLight Rises: Visible Light Communication in the Dark
Visible Light Communication (VLC) emerges as a new wireless communication technology with appealing benefits not present in radio communication. However, current VLC designs commonly require LED lights to emit shining light beams, which greatly limits the applicable scenarios of VLC (e.g., in a sunny day when indoor lighting is not needed). It also entails high energy overhead and unpleasant visual experiences for mobile devices to transmit data using VLC. We design and develop DarkLight, a new VLC primitive that allows light-based communication to be sustained even when LEDs emit extremely-low luminance. The key idea is to encode data into ultra-short, imperceptible light pulses. We tackle challenges in circuit designs, data encoding/decoding schemes, and DarkLight networking, to efficiently generate and reliably detect ultra-short light pulses using off-the-shelf, low-cost LEDs and photodiodes. Our DarkLight prototype supports 1.3-m distance with 1.6-Kbps data rate. By loosening up VLC\u27s reliance on visible light beams, DarkLight presents an unconventional direction of VLC design and fundamentally broadens VLC\u27s application scenarios
MIMO MC-CDMA systems over indoor optical wireless communication channels
Optical wireless communication systems offer a number of advantages over their radio frequency counterparts. The advantages include freedom from fading, freedom from spectrum regulations and abundant bandwidth. The main limitations of optical wireless systems include background noise attributed to natural and artificial light sources and multipath propagation. The former degrades the signal to noise ratio while the latter limits the maximum achievable data rate. This thesis investigates the use of transmit power adaptation in the design of optical wireless spot-diffusing systems to increase the power associated with the main impulse response components, resulting in a compact impulse response and a system that is able to achieve higher data rates. The work also investigates the use of imaging diversity receivers that can reject the background noise components received in directions not associated with the signal. The two techniques help improve the optical wireless system performance. The multibeam transmitter and the multi-detector angle diversity receiver or imaging receiver form a multiple input multiple output (MIMO) system. The work also investigates additional methods that can improve the performance such as transmitter beam angle adaptation, and improved modulation and coding in the form of multi-carrier code division multiple access (MC-CDMA). Furthermore, the work investigates the robustness of a link design that adopts the combination of these methods in a realistic environment with full mobility.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Performances de l'optique sans fil pour les réseaux de capteurs corporels
This thesis deals with the performance of optical girelles communications for body area networks (BAN) as an alternative solution to the radiofrequency one, in the context of mobile healthcare monitoring. After presenting the main characteristics of a BAN using the radiofrequency technology, specifically in the UWB band, we explain the advantages of the optical wireless technology. Diffuse propagation based on infrared technology is then considered for BAN, exploiting optical reflections from environment surfaces. Several optical wireless channel modeling methods are introduced, and we consider two solutions for the link between two on-body nodes: a classical method named “one reflection model”, used to estimate performance variations, and a ray-launching method, used to take into account a great amount of optical reflections. Considering several scenarios, we determine the outage probability, and show that the diffuse optical wireless technology is able to achieve an on-body link, with the data rates and the quality of service required by health monitoring applications, for a transmitted power far lower than the limit defined in standards. Then, we evaluate the theoretical performance, in terms of error probability, of an optical wireless BAN, considering the optical code division multiple access technique. Finally, we show that a BAN using optical wireless technology is theoretically feasible, regarding a health monitoring application, and considering the mobility of the patient in indoor environment.Cette thèse aborde les performances d’un réseau corporel utilisant la technologie optique sans fil, comme alternative aux radiofréquences. L’application visée concerne la télésurveillance de patients mobiles, en milieu hospitalier. Après avoir défini les principales caractéristiques des réseaux corporels radiofréquences, notamment dans le cas de l’ultra large bande, nous présentons les avantages à utiliser la technologie optique sans fil. Nous considérons ensuite cette technologie en infrarouge, avec une méthode de propagation dite diffuse, exploitant les réflexions des rayons optiques dans l’environnement du réseau corporel. Les différentes méthodes de modélisation d’un canal optique diffus sont introduites, et nous utilisons deux types de méthodes pour modéliser le canal entre deux noeuds portés : un modèle classique dit « à une réflexion », permettant d’évaluer rapidement des variations de performances, et une méthode de lancer de rayon pour considérer un grand nombre de réflexions. En utilisant différents scénarios, ainsi que la notion de probabilité de rupture, nous montrons que l’optique diffuse permet de réaliser un lien corporel, pour les débits et la qualité de service requise par une application de télésurveillance médicale, et pour une puissance de transmission très inférieure à la limite imposée par la sécurité oculaire. Finalement, nous étudions les performances théoriques d’un réseau corporel en optique diffuse en termes de probabilité d’erreur, avec une gestion de l’accès multiple réalisé par répartition de codes optiques. Nous concluons qu’un réseau de capteurs corporels en optique diffuse est théoriquement réalisable, pour une application médicale de surveillance de patients mobiles dans l’environnement
Adaptation techniques in optical wireless communications
The need for high-speed local area networks to meet the recent developments
in multimedia and video transmission applications has recently focused interest
on optical wireless communication. Optical wireless systems boast some
advantages over radio frequency (RF) systems, including a large unregulated
spectrum, freedom from fading, confidentiality and immunity against
interference from electrical devices. They can satisfy the dual need for mobility
and broadband networking. However, optical wireless links are not without
flaws. They are affected by background noise (artificial and natural light
sources) and suffer from multipath dispersion. The former can degrade the
signal-to-noise ratio, while the latter restricts the maximum transmission rate
available.
The aim of this thesis is to investigate a number of techniques to overcome
these drawbacks and design a robust high-speed indoor optical wireless system
with full mobility. Beam delay and power adaptation in a multi-spot diffusing
system is proposed in order to increase the received optical signal, reduce the
delay spread and enable the system to operate at higher data rates. The thesis
proposes employing angle diversity receivers and imaging diversity receivers as
in order to reduce background noise components. Moreover, the work
introduces and designs a high-speed fully adaptive optical wireless system that
employs beam delay, angle and power adaptation in a multi-spot diffusing
configuration and investigates the robustness of the link design in a realistic
indoor office. Furthermore, a new adaptive optical wireless system based on a
finite vocabulary of stored holograms is introduced. This method can effectively
optimise the spots’ locations and reduce the design complexity of an adaptive
optical wireless system. A fast adaptation approach based on a divide-andconquer
methodology is proposed and integrated with the system to reduce the
time required to identify the optimum hologram. The trade-off between complexity and performance enhancement of the adaptive finite holograms
methods compared with the original beam power and angle adaptation is
investigated
Otimização do fronthaul ótico para redes de acesso de rádio (baseadas) em computação em nuvem (CC-RANs)
Doutoramento conjunto (MAP-Tele) em Engenharia Eletrotécnica/TelecomunicaçõesA proliferação de diversos tipos de dispositivos moveis, aplicações e serviços
com grande necessidade de largura de banda têm contribuído para o aumento
de ligações de banda larga e ao aumento do volume de trafego das
redes de telecomunicações moveis. Este aumento exponencial tem posto
uma enorme pressão nos mobile operadores de redes móveis (MNOs). Um
dos aspetos principais deste recente desenvolvimento, é a necessidade que as
redes têm de oferecer baixa complexidade nas ligações, como também baixo
consumo energético, muito baixa latência e ao mesmo tempo uma grande
capacidade por baixo usto. De maneira a resolver estas questões, os MNOs
têm focado a sua atenção na redes de acesso por rádio em nuvem (C-RAN)
principalmente devido aos seus benefícios em termos de otimização de performance
e relação qualidade preço. O standard para a distribuição de sinais
sem fios por um fronthaul C-RAN é o common public radio interface (CPRI).
No entanto, ligações óticas baseadas em interfaces CPRI necessitam de uma
grande largura de banda. Estes requerimentos podem também ser atingidos
com uma implementação em ligação free space optical (FSO) que é um sistema
ótico que usa comunicação sem fios. O FSO tem sido uma alternativa
muito apelativa aos sistemas de comunicação rádio (RF) pois combinam a
flexibilidade e mobilidade das redes RF ao mesmo tempo que permitem a
elevada largura de banda permitida pelo sistema ótico. No entanto, as ligações
FSO são suscetíveis a alterações atmosféricas que podem prejudicar
o desempenho do sistema de comunicação. Estas limitações têm evitado o
FSO de ser tornar uma excelente solução para o fronthaul. Uma caracterização
precisa do canal e tecnologias mais avançadas são então necessárias
para uma implementação pratica de ligações FSO. Nesta tese, vamos estudar
uma implementação eficiente para fronthaul baseada em tecnologia
á rádio-sobre-FSO (RoFSO). Propomos expressões em forma fechada para
mitigação das perdas de propagação e para a estimação da capacidade do
canal de maneira a aliviar a complexidade do sistema de comunicação. Simulações
numéricas são também apresentadas para formatos de modulação
adaptativas. São também considerados esquemas como um sistema hibrido
RF/FSO e tecnologias de transmissão apoiadas por retransmissores
que ajudam a alivar os requerimentos impostos por um backhaul/fronthaul
de C-RAN. Os modelos propostos não só reduzem o esforço computacional,
como também têm outros méritos, tais como, uma elevada precisão na estimação
do canal e desempenho, baixo requisitos na capacidade de memória
e uma rápida e estável operação comparativamente com o estado da arte
em sistemas analíticos (PON)-FSO. Este sistema é implementado num recetor
em tempo real que é emulado através de uma field-programmable gate
array (FPGA) comercial. Permitindo assim um sistema aberto, interoperabilidade,
portabilidade e também obedecer a standards de software aberto.
Os esquemas híbridos têm a habilidade de suportar diferentes aplicações,
serviços e múltiplos operadores a partilharem a mesma infraestrutura de
fibra ótica.The proliferation of different mobile devices, bandwidth-intensive applications
and services contribute to the increase in the broadband connections
and the volume of traffic on the mobile networks. This exponential growth
has put considerable pressure on the mobile network operators (MNOs). In
principal, there is a need for networks that not only offer low-complexity,
low-energy consumption, and extremely low-latency but also high-capacity
at relatively low cost. In order to address the demand, MNOs have given significant
attention to the cloud radio access network (C-RAN) due to its beneficial
features in terms of performance optimization and cost-effectiveness.
The de facto standard for distributing wireless signal over the C-RAN fronthaul
is the common public radio interface (CPRI). However, optical links
based on CPRI interfaces requires large bandwidth. Also, the aforementioned
requirements can be realized with the implementation of free space
optical (FSO) link, which is an optical wireless system. The FSO is an appealing
alternative to the radio frequency (RF) communication system that
combines the flexibility and mobility offered by the RF networks with the
high-data rates provided by the optical systems. However, the FSO links are
susceptible to atmospheric impairments which eventually hinder the system
performance. Consequently, these limitations prevent FSO from being an
efficient standalone fronthaul solution. So, precise channel characterizations
and advanced technologies are required for practical FSO link deployment
and operation. In this thesis, we study an efficient fronthaul implementation
that is based on radio-on-FSO (RoFSO) technologies. We propose closedform
expressions for fading-mitigation and for the estimation of channel
capacity so as to alleviate the system complexity. Numerical simulations
are presented for adaptive modulation scheme using advanced modulation
formats. We also consider schemes like hybrid RF/FSO and relay-assisted
transmission technologies that can help in alleviating the stringent requirements
by the C-RAN backhaul/fronthaul. The propose models not only
reduce the computational requirements/efforts, but also have a number of
diverse merits such as high-accuracy, low-memory requirements, fast and
stable operation compared to the current state-of-the-art analytical based
approaches. In addition to the FSO channel characterization, we present
a proof-of-concept experiment in which we study the transmission capabilities
of a hybrid passive optical network (PON)-FSO system. This is
implemented with the real-time receiver that is emulated by a commercial
field-programmable gate array (FPGA). This helps in facilitating an
open system and hence enables interoperability, portability, and open software
standards. The hybrid schemes have the ability to support different
applications, services, and multiple operators over a shared optical fiber
infrastructure
Radio Communications
In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks
Advanced Trends in Wireless Communications
Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics