Browsing by Author "Vieira, Manuel Augusto"
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- Bidirectional data transfer in VLC linksPublication . Louro, Paula; Vieira, Manuela; Vieira, Manuel AugustoVisible Light communication is a data transmission technology that uses the LED lighting infrastructure to simultaneously illuminate and communicate. The ubiquitous existence of LED lamps opened a new opportunity for addressing VLC communication in many indoor communication scenarios. The motivation for the application presented in this paper is the modern, efficient management of warehouses supported by autonomous navigation robots that grab goods and deliver the items at the packaging station. This functionality demands bi-directional communication among infrastructures and vehicles. In this paper we propose links for Infrastructure-To-Vehicle (I2V), Vehicle-ToInfrastructure (V2I) and Vehicle-To-Vehicle (V2V) to perform indoors, bi-directional communication for robot navigation in automated warehouses. In this work it is proposed a bidirectional communication system between a static infrastructure and a mobile robot (I2V). The LED lamps of the warehouse illumination system are used to lighten the space, and to transmit information about position and about racks content. The mobile robots communicate with the infrastructure (V2I) to transmit information on the items that are being removed and carried to the packaging station. The communication among the autonomous robots (V2V) provides information on the number of items intended to be collected when the vehicles are in the same lane, possibly with the purpose of collecting the same items. Different codification schemes are proposed to establish the V2I, I2V and V2V links. Tri-chromatic white LEDs with the red and blue chips modulated at different frequencies and a photodetector based on a-SiC:H/a-Si:H with selective spectral sensitivity are used at the emitter and receiver. Position information is provided by each LED lamp to the autonomous vehicle by adequate modulation of the RGB emitters. The decoding strategy is based on accurate calibration of the output signal. Different scenarios were designed and tested. Requirements related to synchronous transmission and flickering were addressed to enhance the system performance.
- Bidirectional visible light communicationPublication . Louro, Paula; Vieira, Manuela; Vieira, Manuel AugustoVisible light communication (VLC) is a data transmission technology that uses the LED lighting infrastructure to simultaneously illuminate and communicate. The ubiquitous existence of LED lamps opened a new opportunity for addressing VLC in many indoor communication scenarios. The motivation for the presented application is the efficient management of warehouses supported by autonomous navigation robots that grab goods and deliver them at the packaging station. This functionality demands bidirectional communication between infrastructures and vehicles. We propose links for infrastructure-to-vehicle (I2V), vehicle-to-infrastructure (V2I), and vehicle-to-vehicle (V2V) to perform indoors, bidirectional communication. A bidirectional communication system between a static infrastructure and a mobile robot (I2V) is proposed. The LED lamps of the warehouse illumination system are used to lighten the space and to transmit information on position and racks’ contents. The mobile robots communicate with the infrastructure (V2I) to transmit information on the items that are being removed and carried to the packaging station. The communication among robots (V2V) provides information on the number of items intended to be collected when the vehicles are in the same lane. The proposed coding schemes are used as modulation for the ON-OFF keying method. Trichromatic white LEDs and a photodetector based on a-SiC:H/a-Si:H with selective spectral sensitivity are used at the emitter and receiver. Position information is provided by each LED lamp to the vehicle by adequate modulation of the RGB emitters. The decoding strategy is based on accurate calibration of the output signal. Different scenarios were designed and tested. Requirements related to synchronous transmission and flickering were addressed to enhance the system performance. The decoding task is discussed using a bit parity error control methodology to ensure simultaneous detection and correction of bit errors. The consequent increase of bit error rate in the VLC transmission is discussed in the I2V link.
- Capacitive effects in pinpin photodiodesPublication . Fantoni, Alessandro; Fernandes, Miguel; Louro, Paula; Vieira, Manuel Augusto; Vieira, ManuelaThe application of a-SiC:H/a-Si:H pinpin photodiodes for optoelectronic applications as a WDM demultiplexer device has been demonstrated useful in optical communications that use the WDM technique to encode multiple signals in the visible light range. This is required in short range optical communication applications, where for costs reasons the link is provided by Plastic Optical Fibers. Characterization of these devices has shown the presence of large photocapacitive effects. By superimposing background illumination to the pulsed channel the device behaves as a filter, producing signal attenuation, or as an amplifier, producing signal gain, depending on the channel/background wavelength combination. We present here results, obtained by numerical simulations, about the internal electric configuration of a-SiC:H/a-Si:H pinpin photodiode. These results address the explanation of the device functioning in the frequency domain to a wavelength tunable photo-capacitance due to the accumulation of space charge localized at the bottom diode that, according to the Shockley-Read-Hall model, it is mainly due to defect trapping. Experimental result about measurement of the photodiode capacitance under different conditions of illumination and applied bias will be also presented. The combination of these analyses permits the description of a wavelength controlled photo-capacitance that combined with the series and parallel resistance of the diodes may result in the explicit definition of cut off frequencies for frequency capacitive filters activated by the light background or an oscillatory resonance of photogenerated carriers between the two diodes. (C) 2013 Elsevier B.V. All rights reserved.
- Cooperative self-localization and wayfinding services through visible light communicationPublication . Vieira, Manuela; Vieira, Manuel Augusto; Louro, Paula; Fantoni, Alessandro; Vieira, PedroA Visible Light Communication (VLC) cooperative system that supports guidance services and uses an edge/fog based architecture for wayfinding services is presented. The integrated dynamic navigation system consists of multiple transmitters (luminaries) which transmit the map information and path messages necessary for wayfinding. The luminaires used for downlink transmission are equipped with one of two types of controllers: mesh controllers or cellular controllers, which, respectively, forward messages to other devices in the vicinity or to the central manager. Mobile optical receivers, collect the data, extracts theirs location to perform positioning and, concomitantly, the transmitted data from each transmitter. Uplink transmission is implemented and the best route to navigate through venue calculated. Each luminaire, through VLC, reports its geographic position and specific information to the users, making it available for use. Bidirectional communication is implemented and the best route to navigate through venue calculated. Buddy wayfinding services are also considered. Results indicate that the system is able to perform not just the self-localization, but also infer the travel direction and interact with it, optimizing the route to a static or dynamic destination.
- Cooperative vehicular systems: crossroad management through visible lightPublication . Vieira, Manuel Augusto; Vieira, Manuela; Louro, Paula; Vieira, PedroInformation and communication technologies enable optoelectronic cooperative vehicular systems with bi-directional communication, where vehicles communicate with other vehicles, road infrastructures, traffic lights, and vulnerable road users. We use the concept of request/response for the management of a trajectory in a two-way-two-way traffic lights controlled crossroad, using visible-light communication (VLC). The connected vehicles receive information from the network (Infrastructure to Vehicle, I2V), interact with each other (Vehicle to Vehicle, V2V) and with the infrastructure (Vehicle to Infrastructure, V2I), using a request distance and pose estimation concept. In parallel, an intersection manager (IM) coordinates the crossroad and interacts with the vehicles (I2V) using the response distance and the pose estimation concepts. The communication is performed through VLC using the street lamps and the traffic signaling, to broadcast the information. Data are encoded, modulated, and converted into light signals emitted by the transmitters. Tetra-chromatic white sources are used, providing a different data channel for each chip. As receivers and decoders, SiC wavelength division multiplexer (WDM) devices, with light filtering properties, are considered. A simulated vehicle-to-everything (V2X) traffic scenario is presented, and a generic model of cooperative transmission is established. The primary objective is to control the arrival of vehicles to the intersection and schedule them to cross over at time instants that minimize delays. A phasing traffic flow is developed as a proof of concept (PoC). The simulated/experimental results confirm the cooperative VLC architecture. Results show that the communication between connected cars is optimized using a request/response concept and that pose analysis is an important issue to control driver’s behavior in a crossroad. The block diagram conveys that the vehicle’s behavior (successive poses) is influenced by the maneuver permission, by the I2V messages and also by the intersection redesigned layout and presence of other vehicles. An increase in the traffic throughput with least dependency on infrastructure is achieved.
- Cooperative vehicular visible light communication in smarter split intersectionsPublication . Vieira, Manuel Augusto; Vieira, Manuela; Louro, Paula; Vieira, PedroThis paper addresses the issues related to the Visible Light Communication (VLC) usage in vehicular communication applications. We propose a Visible Light Communication system based on Vehicle-to-Vehicle, Vehicle-to-Infrastructure and Infrastructure-to-Vehicle communications able to safely manage vehicles crossing through an intersection leveraging Edge of Things facilities. By using the streetlamps, street lights and traffic signaling to broadcast information, the connected vehicles interact with one another and with the infrastructure. By using joint transmission, mobile optical receivers collect data at high frame rates, calculate their location for positioning and, concomitantly, read the transmitted data from each transmitter. In parallel with this, an intersection manager coordinates traffic flow and interacts with the vehicles via Driver Agents embedded in them. A communication scenario is stablished and a “mesh/cellular” hybrid network configuration proposed. Data is encoded, modulated and converted into light signals emitted by the transmitters. As receivers and decoders, optical sensors with light filtering properties, are used. Bidirectional communication between the infrastructure and the vehicles is tested. To command the passage of vehicles crossing the intersection safely queue/request/response mechanisms and temporal/space relative pose concepts are used. Results show that the short range mesh network ensures a secure communication from street lamp controllers to the edge computer through the neighbor traffic light controller with active cellular connection and enables peer-to-peer communication, to exchange information between V-VLC ready connected cars. The innovative treatments for the congested intersections are related with the introduction of the split intersection. In the split intersection a congested two-way-two-way traffic light controlled intersection was transformed into two lighter intersections which facilitate a smoother flow with less driver delay by reducing the number of vehicle signal phases. Based on the results, the V-VLC system provides direct monitoring of critical points including queue formation and dissipation, relative speed thresholds and inter-vehicle spacing, increasing safety.
- Decoding techniques for indoors navigation using VLCPublication . Louro, Paula; Vieira, Manuela; Vieira, Manuel AugustoIn recent years, devices with wireless communication capabilities have generated a growing interest in indoor navigation. Indoor localization and proximity detection is becoming increasingly attractive due to the emergence of the Internet of Things (IoT) and the inherent end-to-end connectivity of billions of devices. In a closed space, GPS has poor, unreliable performance, requiring alternative techniques and wireless technologies. In this paper, we propose the use of Visible Light Communication (VLC) to support guidance and communication for signaling in an indoor environment. Research focuses mainly on the development of navigation VLC systems, transmission of control data information, and decoding techniques. The communication system uses RGB white LEDs as emitters and pinpin photodiodes with selective spectral sensitivity as receivers. Downlink communication is established between the infra-structure and the mobile user. The decoding strategy is based on accurate calibration of the output signal and uses bit error control methods to reduce the BER of the system. In this paper, we will describe the coding schemes and decoding algorithms, as well as the characteristics of transmitters and receivers.
- DEMUX devices based on a-SiC:HPublication . Fantoni, Alessandro; Louro, Paula; Vieira, Manuel Augusto; Silva, T.; Vieira, ManuelaIn this paper we present results about the functioning of a multilayered a-SiC:H heterostructure as a device for wavelength-division demultiplexing of optical signals. The device is composed of two stacked p-i-n photodiodes, both optimized for the selective collection of photogenerated carriers. Band gap engineering was used to adjust the photogeneration and recombination rates profiles of the intrinsic absorber regions of each photodiode to short and long wavelength absorption and carrier collection in the visible spectrum. The photocurrent signal using different input optical channels was analyzed at reverse and forward bias and under steady state illumination. This photocurrent is used as an input for a demux algorithm based on the voltage controlled sensitivity of the device. The device functioning is explained with results obtained by numerical simulation of the device, which permit an insight to the internal electric configuration of the double heterojunction.These results address the explanation of the device functioning in the frequency domain to a wavelength tunable photocapacitance due to the accumulation of space charge localized at the internal junction. The existence of a direct relation between the experimentally observed capacitive effects of the double diode and the quality of the semiconductor materials used to form the internal junction is highlighted.
- Detection of change in fluorescence between reactive cyan and the yellow fluorophores using a-SiC:H multilayer transducersPublication . Louro, Paula; Vaz da Silva, V; Vieira, Manuel Augusto; Vieira, ManuelaThe transducer consists of a semiconductor device based on two stacked -i-n heterostructures that were designed to detect the emissions of the fluorescence resonance energy transfer between fluorophores in the cyan (470 nm) and yellow (588 nm) range of the spectrum. This research represents a preliminary study on the use of such wavelength-sensitive devices as photodetectors for this kind of application. The device was characterized through optoelectronic measurements concerning spectral response measurements under different electrical and optical biasing conditions. To simulate the fluorescence resonance energy transfer (FRET) pairs, a chromatic time-dependent combination of cyan and yellow wavelengths was applied to the device. The generated photocurrent was measured under reverse and forward bias to read out the output photocurrent signal. A different wavelength-biasing light was also superimposed. Results show that under reverse bias, the photocurrent signal presents four separate levels, each one assigned to the different wavelength combinations of the FRET pairs. If a blue background is superimposed, the yellow channel is enhanced and the cyan suppressed, while under red irradiation, the opposite behavior occurs. So, under suitable biasing light, the transducer is able to detect separately the cyan and yellow fluorescence pairs. An electrical model, supported by a numerical simulation, supports the transduction mechanism of the device.
- Dynamic VLC navigation system in crowded buildingsPublication . Vieira, Manuela; Vieira, Manuel Augusto; Louro, Paula; Fantoni, Alessandro; Vieira, PedroThis paper investigates the applicability of an intuitive risk of transmission wayfinding system in public spaces, virtual races, indoor large environments and complex buildings using Visible Light Communication (VLC). Typical scenarios include: finding places, like a particular shop or office, guiding users across different floors, and through elevators and stairs. The system is able to inform the users, in real time, not only of the best route to the desired destination, through a route without clusters of users, but also of crowded places. Data from the sender is encoded, modulated and converted into light signals emitted by the transmitters. Tetra chromatic white sources are used providing a different data channel for each chip. At the receiver side, the modulated light signal, containing the ID and the 3D geographical position of the transmitter and wayfinding information, is received by a SiC optical sensor with light filtering and demultiplexing properties. Since lighting and wireless data communication is combined, each luminaire for downlink transmission becomes a single cell, in which the optical Access Point (AP) is located in the ceiling and the mobile users are scattered across the overlap discs of each cell, underneath. The light signals emitted by the LEDs are interpreted directly by the receivers of the positioned users. Bidirectional communication is tested. The effect of the location of the Aps is evaluated and a 3D model for the cellular network is analyzed. In order to convert the floorplan to a 3D geometry, a tandem of layers in a orthogonal topology is used, and a 3D localization design, demonstrated by a prototype implementation, is presented. Uplink transmission is implemented, and the 3D best route to navigate through venue is calculated. Buddy wayfinding services are also considered. The results showed that the dynamic VLC navigation system enables to determine the position of a mobile target inside the network, to infer the travel direction along the time, to interact with received information and to optimize the route towards a static or dynamic destination.