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- SiC multilayer photonic structures with self optical bias amplificationPublication . Vieira, Manuela; Vieira, Manuel Augusto; Louro, Paula; Fantoni, Alessandro; Barata, Manuel; Vaz da Silva, VCharacteristics of tunable wavelength pi'n/pin filters based on a-SiC:H multilayered stacked cells are studied both experimental and theoretically. Results show that the device combines the demultiplexing operation with the simultaneous photodetection and self amplification of the signal. An algorithm to decode the multiplex signal is established. A capacitive active band-pass filter model is presented and supported by an electrical simulation of the state variable filter circuit. Experimental and simulated results show that the device acts as a state variable filter. It combines the properties of active high-pass and low-pass filter sections into a capacitive active band-pass filter using a changing photo capacitance to control the power delivered to the load.
- 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.
- Stacked photo-sensing devices based on SiC alloys A non-pixelled architecture for imagers and demultiplexing devicesPublication . Vieira, Manuela; Louro, Paula; Fernandes, Miguel; Fantoni, Alessandro; Vieira, Manuel Augusto; Costa, JoãoIn this review paper different designs based on stacked p-i'-n-p-i-n heterojunctions are presented and compared with the single p-i-n sensing structures. The imagers utilise self-field induced depletion layers for light detection and a modulated laser beam for sequential readout. The effect of the sensing element structure, cell configurations (single or tandem), and light source properties (intensity and wavelength) are correlated with the sensor output characteristics (light-to-dark sensivity, spatial resolution, linearity and S/N ratio). The readout frequency is optimized showing that scans speeds up to 104 lines per second can be achieved without degradation in the resolution. Multilayered p-i'-n-p-i-n heterostructures can also be used as wavelength-division multiplexing /demultiplexing devices in the visible range. Here the sensor element faces the modulated light from different input colour channels, each one with a specific wavelength and bit rate. By reading out the photocurrent at appropriated applied bias, the information is multiplexed or demultiplexed and can be transmitted or recovered again. Electrical models are present to support the sensing methodologies.
- 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.
- Photodetector with integrated optical thin film filtersPublication . Vieira, Manuel Augusto; Vieira, Manuela; Louro, Paula; Vaz da Silva, V; Garção, A. S.This paper reports on optical filters based on a-SiC:H tandem pi'n/pin heterostructures. The spectral sensitivity is analyzed. Steady state optical bias with different wavelengths are applied from each front and back sides and the photocurrent is measured. Results show that it is possible to control the sensitivity of the device and to tune a specific wavelength range by combining radiations with complementary light penetration depths. The transfer characteristics effects due to changes in the front and back optical bias wavelength are discussed. Depending on the wavelength of the external background and irradiation side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. The output waveform presents a nonlinear amplitude-dependent response to the wavelengths of the input channels.
- Redesign of the trajectory within a complex intersection for visible light communication ready connected carsPublication . Vieira, Manuel Augusto; Vieira, Manuela; Louro, Paula; Vieira, PedroTo serve the changing needs of road traffic control, the road space and road structure surrounding an intersection have evolved into complex forms. The redesign of the trajectories, though complex, can be accomplished by the application of methods for navigation, guidance, and combination of expert knowledge of road traffic control of vehicles, using a concept of request/response in a two-way-to-way traffic light-controlled crossroad. The communication between the infrastructures and the vehicles (I2V), between vehicles (V2V), and from the vehicles to the infrastructures (V2I) is performed through visible light communication (VLC) using the street lamps and the traffic signaling to broadcast the information. Vehicle headlamps and taillights are used to transmit data to other vehicles or infrastructures allowing digital safety and data privacy. 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, silicon/carbon wavelength division multiplexer devices, with light filtering properties, are used. The primary objective is to control the arrival of vehicles to an intersection and schedule them to cross at times that minimize delays. A further objective is to allocate delays between left-turns and forward movements, moderating the speed and slot between vehicles traveling in these directions, maintaining a safe distance from one to another. Pedestrians and bicycles are incorporated. A I2V2V2I traffic scenario is established. A phasing traffic flow is developed as a proof of concept. The experimental results confirm the cooperative VLC architecture showing that communication between connected cars is optimized.
- Indoor wayfinding using visible light communicationPublication . Vieira, Manuela; Vieira, Manuel Augusto; Louro, Paula; Fantoni, Alessandro; Vieira, PedroOptical wireless communication has been widely studied during the last years in short-range applications. This paper investigates the applicability of an intuitive wayfinding system in complex buildings using Visible Light Communication (VLC). Typical scenarios include finding places, like a particular shop or office, guiding users across different floors, through elevators and stairs. 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 SiC photodetector with light filtering and demultiplexing properties. Since lighting and wireless data communication is combined, each luminaire for downlink transmission become a single cell, in which the optical access point (AP) is located in the ceiling and the mobile users are scattered within the overlap discs of each cells underneath. The light signals emitted by the LEDs are interpreted directly by the receivers of the users positioned underneath. The effect of the location of the Aps is evaluated and a model for the different cellular networks is analyzed. Orthogonal topologies are tested, 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 calculated. Buddy wayfinding services are also implemented. The results showed that the system make possible to determine the position of a mobile target inside the network, to infer the travel direction along the time and to interact with information received and to optimize the route towards a static or dynamic destination.
- Trajectory redesign within a complex intersection for VLC ready connected carsPublication . Vieira, Manuel Augusto; Vieira, Manuela; Louro, Paula; Vieira, PedroIn order to serve the changing needs of road traffic control, the road space and road structure surrounding an intersection have evolved into complex forms. Using a new concept of request/response in a two-way-to-way traffic light controlled crossroad, the redesign of the trajectories can be accomplished by the application of methods for navigation, guidance and combination of expert knowledge of vehicle road traffic control. In this work, the communication between the Infrastructures and the Vehicles (I2V), between vehicles (V2V) and from the Vehicles to the Infrastructures (V2I) is performed through Visible Light Communication (VLC), using the street lamps and the traffic signaling to broadcast the information. Vehicle headlamps are used to transmit data to other vehicles or infrastructures, allowing digital safety and data privacy. Data 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. As receivers and decoders, SiC Wavelength Division Multiplexer (WDM) devices, with light filtering properties, are considered. The primary objective is to control the arrival of vehicles to an intersection and schedule them to cross at times that minimize traffic delay. A further objective is to allocate delays between left-turns and forward movements, moderating the speed and slot between vehicles travelling in these directions, maintaining a safe distance from one to another. Pedestrians and bicycles are also incorporated. An I2V2V2I traffic scenario is proposed, and bidirectional communication between the infrastructure and the vehicles is tested, using the VLC request/response concept. A phasing traffic flow is developed as a proof of concept. The experimental results confirm the cooperative VLC architecture, showing that communication between connected cars and infrastructures can be optimized using the mentioned request/response concept. A significant increase in traffic throughput with the least dependency on infrastructure is achieved.
- 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.
- VLC-based geo-localization for automated logistics control using AVGsPublication . Louro, Paula; Rodrigues, João; Vieira, Manuela; Vieira, Manuel Augusto; Vieira, PedroIncreasing interest in indoor navigation has recently been generated by devices with wireless communication capabilities that enabled a wide range of applications and services. The rise of the Internet of Things (IoT) and the inherent end-to end connectivity of billions of devices is very attractive for indoor localization and proximity detection. Other fields, such as, marketing and customer assistance, health services, asset management and tracking, can also benefit from indoor localization. Different techniques and wireless technologies have been proposed for indoor location, as the traditional Global Positioning System (GPS) has a very poor, unreliable performance in a closed space. The work presented in this research proposes the use of an indoor localization system based on Visible Light Communication (VLC) to support the navigation and operational tasks of Autonomous Guided Vehicles (AVG) in an automated warehouse. The research is mainly focused on the development of the navigation VLC system, transmission of control data information and decoding techniques. As part of the communication system, trichromatic white LEDs are used as emitters and a-SiC:H/a-Si:H based photodiodes with selective spectral sensitivity, are used as receivers. Through the modulation of the RGB LEDs, the downlink channel establishes an infrastructure-to-vehicle link (I2V) and provides position information to the vehicle. The decoding strategy is based on accurate calibration of the output signal. Characterization of the transmitters and receivers, description of the coding schemes and decoding algorithms will be the focus of discussion in this paper.