Desenho da camada DLL para sistemas de comunicação por luz visível

Mestrado em Engenharia Electrónica e TelecomunicaçõesWith the advent of the Information Age, communication systems have become the backbone of our society. The modern society strives to nd instant access to speci c sources of information to make time-constrained decisions. Therefore, the twenty- rst century is marked by a growing demand for bandwidth in wireless communications, as it allows users to communicate and access daily applications even from remote areas. Up to the present time, numerous breakthroughs in wireless communications were accomplished but mainly using the radio portion of the electromagnetic spectrum, which made RF to take the central role in today's communication systems. However, RF technology is a victim of its own success. Due to the tremendous increase in the number of mobile devices, RF technology cannot cope much longer with this market demand and will eventually reach a saturation point. VLC is a recently appealing technique in the eld of wireless communications that intends to complement RF technologies and is sought by many researchers as a viable alternative. VLC based on Light Emitting Diode (LED) takes advantage of these solid-state devices superior modulation capability to transmit data while assuring their lighting functionality. This work addresses the problem of achieving high bandwidth in a DLL design for OFDM based VLC broadcast systems and is inserted in a funded project called VLCLighting. The main objective of this dissertation work is to implement an e cient DLL in a Microblaze soft processor in a FPGA and to study its usage in a broadcast VLC system for lighting systems. Since two value added services were identi ed in the VLCLighting project, the proposed DLL aims at furnishing the adequate means to fragment and route those services requests while maintaining a continuous transmission ow that assures lighting and transceiver functionality. This work proposes a DLL design that was inspired in DVB and project OMEGA systems, able to describe the required amendments to full ll VLCLighting goals.Com a chegada da era da Informação, os sistemas de comunicação tornaram-se na espinha dorsal da nossa sociedade. A Sociedade Moderna esforça-se por ter acesso instantâneo a fontes de informação específicas para tomar decisões limitadas pelo tempo. Portanto, o século XXI está marcado pela crescente exigência da largura de banda nas comunicações sem fios, pois tal permite aos utilizadores comunicarem e acederem as aplicações a partir de áreas longínquas. Até ao momento, foram alcançados diversos avanços/descobertas na largura de banda das comunicações sem fos, mas tal tem sido conseguido usando o intervalo de radiofrequências (RF) do espectro eletromagnético e que fez com que o RF ficasse com o papel principal nos sistemas de comunicação de hoje. Contudo, a Tecnologia RF e vitima do seu próprio sucesso. Devido ao tremendo aumento do número de aparelhos de comunicação móveis, a tecnologia RF não pode lidar muito mais tempo com a exigência dos mercados e atingirá o seu ponto de saturação. VLC (Comunicação através de luz visivel) é uma tecnica recente muito apelativa no campo das comunicações sem-fios e que pretende ser um complemento à tecnologia RF, sendo considerada por muitos investigadores como uma alternativa viável. Esta dissertação discute o problema de se alcançar uma grande taxa de transmissão com a implementação de uma Data Link Layer (DLL) direccionada para sistemas VLC com modulação OFDM e está inserida num projecto financiado intitulado VLCLighting. O objectivo principal desta dissertação consiste na implementação de um DLL eficiente num processador Microblaze numa Field-Programmable Gate Array (FPGA) e no estudo da sua utilização em sistemas VLC para uso combinado em sistemas de iluminação. Uma vez que foram identificados dois serviços com valor acrescentado para serem incluídos no projecto VLCLighting, a proposta DLL pretende fornecer os meios necessários á fragmentação e encaminhamento das exigências dos serviços, enquanto se mantêm um fluxo contínuo de transmissão capaz de assegurar as funcionalidades de iluminação e comunicação. A presente dissertação propõe um desenho inspirado nos sistemas DVB e do projeto OMEGA, e descrevendo as alterações exigidas para satisfazer os objectivos do projecto VLCLighting

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

Enhanced carrierless amplitude and phase modulation for optical communication systems

This thesis develops and investigates enhanced techniques for carrierless amplitude and phase modulation (CAP) in optical communication systems. The CAP scheme is studied as the physical layer modulation technique due to its implementation simplicity and versatility, that enables its implementation as a single carrier (CAP) or multi-carrier technique (m-CAP). The effect of timing jitter on the error performance of CAP is first investigated. The investigation indicates that synchronization is a critical requirement for CAP receiver and as a result, a novel low-complexity synchronization algorithm is developed with experimental demonstration for CAP-based visible light communication (VLC) systems. To further reduce the overall link complexity, a fractionally-spaced equalizer (FSE) is considered to mitigate the effects of inter-symbol interference (ISI) and timing jitter. The FSE implementation, which eliminates the need for a separate synchronization block, is shown through simulation and VLC experimental demonstration to outperform symbol-spaced equalizers (SSE) that are reported in literature for CAP-based VLC systems. Furthermore, in this thesis, spectrally-efficient index modulation techniques are developed for CAP. The proposed techniques can be divided into two broad groups, namely spatial index CAP (S-CAP) and subband index CAP (SI-CAP). The proposed spatial index techniques leverage the fact that in VLC, multiple optical sources are often required. The spatial CAP (S-CAP) transmits CAP signal through one of Nt available LEDs. It is developed to reduce equalization requirement and improve the spectral efficiency of the conventional CAP. In addition to the bits transmitted through the CAP symbol, the S-CAP encodes additional bits on the indexing/spatial location of the LEDs. The generalised S-CAP (GS-CAP) is further developed to relax the S-CAP limitation of using a single LED per symbol duration. In addition to the S-CAP scheme, multiple-input multiple-output (MIMO) techniques of repetitive-coded CAP (RC-CAP) and spatial multiplexing CAP (SMux-CAP) are investigated for CAP. Low-complexity detectors are also developed for the MIMO schemes. A key challenge of the MIMO schemes is that they suffer power penalty when channel gains are similar, which occur when the optical sources are closely located. The use of multiple receivers and power factor imbalance (PFI) techniques are proposed to mitigate this power penalty. The techniques result in significant improvement in the power efficiency of the MIMO schemes and ensure that the spectral efficiency gain is obtained with little power penalty. Finally, subband index CAP (SI-CAP) is developed to improve the spectral efficiency of m-CAP and reduce its peak-to-average power ratio (PAPR). The SI-CAP encodes additional information bits on the selection of ‘active’ subbands of m-CAP and only modulate data symbols on these ‘active’ subbands. The error performance of the proposed SI-CAP is evaluated analytically and verified with computer-based simulations. The SI-CAP technique is also experimented for both VLC and step-index plastic optical fibre (SI-POF) communication links. The experimental results show that for a fixed power efficiency, SI-CAP achieves higher data rate compared tom-CAP. For example, at a representative bit error rate (BER) of 10-5, the SI-CAP achieves a data rate and power efficiency gain of 26:5 Mb/s and 2:5 dB, respectively when compared to m-CAP. In addition, an enhanced SI-CAP (eSI-CAP) is developed to address the complexity that arises in SI-CAP at higher modulation order. The results of the experimental demonstrations in VLC and 10 m SI-POF link shows that when compared with m-CAP, eSI-CAP consistently yields a data rate improvement of between 7% and 13% for varying values of the SNR

Spectrum and energy efficient digital modulation techniques for practical visible light communication systems

The growth in mobile data traffic is rapidly increasing in an unsustainable direction given the radio frequency (RF) spectrum limits. Visible light communication (VLC) offers a lucrative solution based on an alternative license-free frequency band that is safe to use and inexpensive to utilize. Improving the spectral and energy efficiency of intensity modulation and direct detection (IM/DD) systems is still an on-going challenge in VLC. The energy efficiency of inherently unipolar modulation techniques such as pulse-amplitude modulation discrete multitone modulation (PAM-DMT) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) degrades at high spectral efficiency. Two novel superposition modulation techniques are proposed in this thesis based on PAM-DMT and ACO-OFDM. In addition, a practical solution based on the computationally efficient augmented spectral efficiency discrete multi-tone (ASE-DMT) is proposed. The system performance of the proposed superposition modulation techniques offers significant electrical and optical power savings with up to 8 dB in the electrical signal-to-noise ratio (SNR) when compared with DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM). The theoretical bit error ratio (BER) performance bounds for all of the proposed modulation techniques are in agreement with the Monte-Carlo simulation results. The proposed superposition modulation techniques are promising candidates for spectrum and energy efficient IM/DD systems. Two experimental studies are presented for a VLC system based on DCO-OFDM with adaptive bit and energy loading. Micrometer-sized Gallium Nitride light emitting diode (m-LED) and light amplification by stimulated emission of radiation diode (LD) are used in these studies due to their high modulation bandwidth. Record data rates are achieved with a BER below the forward error correction (FEC) threshold at 7.91 Gb/s using the violet m-LED and at 15 Gb/s using the blue LD. These results highlight the potential of VLC systems in practical high speed communication solutions. An additional experimental study is demonstrated for the proposed superposition modulation techniques based on ASE-DMT. The experimentally achieved results confirm the theoretical and simulation based performance predictions of ASE-DMT. A significant gain of up to 17.33 dB in SNR is demonstrated at a low direct current (DC) bias. Finally, the perception that VLC systems cannot work under the presence of sunlight is addressed in this thesis. A complete framework is presented to evaluate the performance of VLC systems in the presence of solar irradiance at any given location and time. The effect of sunlight is investigated in terms of the degradations in SNR, data rate and BER. A reliable high speed communication system is achieved under the sunlight effect. An optical bandpass blue filter is shown to compensate for half of the reduced data rate in the presence of sunlight. This thesis demonstrates data rates above 1 Gb/s for a practical VLC link under strong solar illuminance measured at 50350 lux in clear weather conditions

Visible Light Optical Camera Communication for Electroencephalography Applications

Due to the cable-free deployment and flexibility of wireless communications, the data transmission in the applications of home and healthcare has shown a trend of moving wired communications to wireless communications. One typical example is electroencephalography (EEG). Evolution in the radio frequency (RF) technology has made it is possible to transmit the EEG data without data cable bundles. However, presently, the RF-based wireless technology used in EEG suffers from electromagnetic interference and might also have adverse effects on the health of patient and other medical equipment used in hospitals or homes. This puts some limits in RF-based EEG solutions, which is particularly true in RF restricted zones like Intensive Care Units (ICUs). As a recently developed optical wireless communication (OWC) technology, visible light communication (VLC) using light-emitting diodes (LEDs) for both simultaneous illumination and data communication has shown its advantages of free from electromagnetic interference, potential huge unlicensed bandwidth and enhanced data privacy due to the line transmission of light. The most recent development of VLC is the optical camera communication (OCC), which is an extension of VLC IEEE standard 802.15.7, also referred to as visible light optical camera communication (VL-OCC). Different from the conventional VLC where traditional photodiodes are used to detect and receive the data, VL-OCC uses the imaging camera as the photodetector to receive the data in the form of visible light signals. The data rate requirement of EEG is dependent on the application; hence this thesis investigates a low cost, organic LED (OLED)-driven VL-OCC wireless data transmission system for EEG applications