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- Footprint model in a navigation system based on visible light communicationPublication . Louro, Paula; Vieira, Manuela; Vieira, Manuel; Lima, Mirtes de; Rodrigues, João; Vieira, PedroIndoor navigation is hardly managed by the usual Global Positioning System (GPS) due to the strong attenuation of signals inside the buildings. Alternative based on RF optical, magnetic or acoustic signals can be used. Among the optical technologies, Visible Light Communication (VLC) provides good position accuracy. The proposed system uses commercial RGB white LEDs for the generation of the light, which is simultaneously coded and modulated to transmit information. The receiver includes a multilayered photodetector based on a-SiC:H operating in the visible spectrum. The positioning system includes multiple, identical navigation cells. Inside each cell, the optical pattern defined by the VLC transmitters establishes specific spatial regions assigned each to different optical excitations, which configures the footprint of the navigation cell. Demodulation and decoding procedures of the photocurrent signal measured by the photodetector are used to identify the input optical excitations and enable position recognition inside the cell. The footprint model is characterized using geometrical and optical assumptions, namely the Lambertian model for the LEDs and the evaluation of the channel gain of the VLC link. An algorithm to decode the information is established and the positioning accuracy is discussed. The experimental results confirmed that the proposed VLC architecture is suitable for the intended application.
- Cooperative vehicular communication systems based on visible light communicationPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Vieira, PedroThe use of visible light communication (VLC) in vehicular communication systems for vehicle safety applications is proposed. The system aims to ensure the communication between a LED-based VLC emitter and an on-vehicle VLC receiver. A traffic scenario is established. Vehicle-to-vehicle (V2V) and infrastructure-to-vehicle (12V) communications are analyzed. For the V2V communication study, the emitter was developed based on the vehicle headlights, whereas for the study of 12V communication system, the emitter was built based on streetlights. The VLC receiver is based on amorphous SiC technology and enhances the conditioning of the signal enabling to decode the transmitted information. Receivers are located at the rooftop of the vehicle, for 12V communications, and at the tails for V2V reception. Clusters of emitters, in a square topology, are used in the 12V transmission. The information and the ID code of each emitter in the network are sent simultaneously by modulating the individual chips of the trichromatic white LED. Free space is the transmission medium. An on-off code is used to transmit data. An algorithm to decode the information at the receivers is set. The proposed system was tested. The experimental results confirmed that the proposed cooperative VLC architecture is suitable for the intended applications.
- Bi-directional communication between infrastructures and vehicles through visible lightPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Vieira, PedroIn this paper a vehicular communication system that incorporates illumination, signaling, communications, and positioning functions is presented. The bidirectional 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 LEDs to broadcast the information. As receivers and decoders, pin/pin SiC Wavelength Division Multiplex (WDM) photodetectors, with light filtering properties, are being used. White polychromatic-LEDs are used for lighting and to implement the WDM. This allows modulating separate data streams on four colors which together multiplex to white light. A traffic scenario is proposed, along with the transmitter to receiver setup. The performance of a cooperative driving system is evaluated. To achieve cooperative vehicular communications (I2V2V2I2V), streams of messages containing the ID physical address of the emitters are used, transmitting a codeword that is received and decoded by the receivers. As a proof of concept, a I2V2V2IV traffic scenario is presented, bidirectional communication between the infrastructures and the vehicles is established and tested. The experimental results confirm that the cooperative vehicular VLC architecture is a promising approach concerning communications between road infrastructures and cars, fulfilling data privacy.
- Design of a transmission system for indoors navigation based on VLCPublication . Louro, Paula; Rodrigues, F.; Costa, João; Vieira, Manuel; Vieira, ManuelaIn this research we present a system based on Visible Light Communication (VLC) with the dual purpose of indoor positioning and data transmission. We propose a system based on RGB white LEDs and a pinpin phototetector based on a-SiC:H/a-Si:H to detect the optical signals transmitted y the modulated emitters of the LEDs. A unit navigation cell is defined and characterized by a unique identifier, and the concept is enlarged to adjacent cells. Within each cell, each spatial region is assigned by the optical pattern of the correspondent emitters. Besides, the positioning and navigation functionality, additional data transmission is also demonstrated using four different channels in each navigation cell. A specific codification scheme and decoding algorithm are proposed and discussed. Error control methodology is also presented to enhance the decoding process. In this research we present a system based on Visible Light Communication (VLC) with the dual purpose of indoor positioning and data transmission. We propose a system based on RGB white LEDs and a pinpin phototetector based on a-SiC:H/a-Si:H to detect the optical signals transmitted y the modulated emitters of the LEDs. A unit navigation cell is defined and characterized by a unique identifier, and the concept is enlarged to adjacent cells. Within each cell, each spatial region is assigned by the optical pattern of the correspondent emitters. Besides, the positioning and navigation functionality, additional data transmission is also demonstrated using four different channels in each navigation cell. A specific codification scheme and decoding algorithm are proposed and discussed. Error control methodology is also presented to enhance the decoding process.
- On the use of visible light communication in cooperative vehicular communication systemsPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Vieira, PedroThe paper proposes the use of Visible Light Communication (VLC) in Vehicular Communication Systems for vehicle safety applications. A smart vehicle lighting system that combines the functions of illumination, signaling, communications, and positioning is presented. The system aims to ensure the communication between a LED based VLC emitter and an on-vehicle VLC receiver. A traffic scenario is stablished. Vehicle-to-vehicle (V2V) and Infrastructure-to-Vehicle (I2V) communications are analyzed. For the V2V communication study, the emitter was developed based on the vehicle head lights, whereas for the study of I2V communication system, the emitter was built based on streetlights. The VLC receiver is used to extract the data from the modulated light beam coming from the white RGB-LEDs emitters. The VLC receiver is based on amorphous SiC technology and enhances the conditioning of the signal enabling to decode the transmitted information. The [p(SiC:H)/i(SiC:H)/n(SiC:H)/p(SiC:H)/i(Si:H)/n(Si:H)] tandem photodetectors are located at the roof-top of the vehicle, for I2V communications, and at the tails for V2V reception. Clusters of emitters, in a square topology, are used in the I2V transmission. The information and the ID code of each emitter in the network are sent, simultaneously, by modulating the individual chips of the trichromatic white LED. Free space is the transmission medium. An on-off code is used to transmit data. An algorithm to decode the information at the receivers is set. The proposed system was tested. The experimental results, confirmed that the proposed cooperative VLC architecture is suitable for the intended applications.
- Transmission of signals using white LEDs for VLC applicationsPublication . Louro, Paula; Silva, V.; Rodrigues, I.; Vieira, Manuel; Vieira, ManuelaIn this paper an integrated wavelength optical filter and photodetector for Visible Light Communication (VLC) is used. The proposed application uses indoor warm light lamps lighting using ultra-bright white LEDs pulsed at frequencies higher than the ones perceived by the human eye. The system was analyzed using two different types the white LEDs, namely, phosphor and trichromatic based LEDs. The signals were transmitted into free space and the generated photocurrent was measured by the pin-pin photodetector based on a-SiC:H/a-Si:H. This device operates in the visible spectrum, allowing thus the detection of the pulsed white light emitted by the LEDs. However, as it also works as a visible optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light, it is able to detect different wavelengths. This feature allows the detection of the individual components of the tri-chromatic white LED, which enlarges the amount of information transmitted by this type of white LED, when compared to the phosphor based LED. A capacitive optoelectronic model supports the experimental results and the physical operation of the device. A numerical simulation is presented.
- On-off keying transmitter design for navigation by visible light communicationPublication . Louro, Paula; Vieira, Manuela; Costa, João; Vieira, ManuelWhite LEDS revolutionized the field of illumination technology mainly due to the energy saving effects. Besides lighting purposes LEDs can also be used in wireless communication systems when integrated in Visible Light Communication (VLC) systems. Indoor positioning for navigation in large buildings is currently under research to overcome the difficulties associated with the use of GPS in such environments. The motivation for this application is also supported by the possibility of taking advantage of an existing lighting and WiFi infrastructure. In this work it is proposed an indoor navigation system based on the use of VLC technology. The proposed system includes trichromatic white LEDs with the red and blue chips modulated at different frequencies and a pinpin photodetector with selective spectral sensitivity. Optoelectronic features of both optical sources and photodetector device are analyzed. The photodetector device consists two pin structures based on a-SiC:H and a-Si:H with geometrical configuration optimized for the detection of short and large wavelengths in the visible range. Its sensitivity is externally tuned by steady state optical bias. The localization algorithm makes use of the Fourier transform to identify the frequencies present in the photocurrent signal and the wavelength filtering properties of the sensor under front and back optical bias to detect the existing red and blue signals. The viability of the system was demonstrated through the implementation of an automatic algorithm to infer the photodetector cardinal direction. A capacitive optoelectronic model supports the experimental results and explains the device operation.
- Vehicular visible light communicationin a two-way-two-way traffic light controlled crossroadPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Lima, Mirtes de; Vieira, PedroThe concept of request/response and relative pose estimation for the management of the trajectory is used, in a two-way-two-way traffic lights controlled crossroad, using Vehicular Visible Light Communication (V-VLC). The connected vehicles receive information from the network and interact with each other and with the infrastructure. In parallel, an Intersection Manager (IM) coordinates the crossroad and interacts with the vehicles using the temporal/space relative pose concepts. V-VLC is performed using the street lamps, the traffic signaling and the headlamps to broadcast the information. 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. Cooperative localization is realized in a distributed way with the incorporation of the indirect vehicle-to-vehicle relative pose estimation method. A phasing traffic flow is developed, as Proof of Concept (PoC) and a generic model of cooperative transmission is analysed. Results expresses that the vehicle’s behavior (successive poses) is mainly influenced by the manoeuvre permission and presence of other vehicles.
- Up/down link data transmission for indoor navigation based on visible light communicationPublication . Louro, Paula; Vieira, Manuela; Vieira, ManuelIndoor navigation based on Visible Light communication (VLC) are attractive solutions for Indoor Positioning Systems, as Global Positioning Systems signals are strongly absorbed by the buildings and other wireless solutions need to be used. In this work it is proposed an indoor navigation system based on VLC technology for assisting warehouse management with autonomous vehicles. The system is designed to establish bidirectional communication between a static infrastructure and the mobile picking robot. Data transmission uses white tri-chromatic LEDs as optical emitters, a dedicated photodetector with selective spectral sensitivity and different coding schemes designed to ensure synchronization between frames, to shield the decoding process from errors and to minimize flickering effects.
- Visible light communication in a traffic controlled Split intersectionPublication . Vieira, Manuel; 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. The redesign or split 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. A proposed innovative treatment for congested urban is the split intersection. It facilitates a smoother flow with less driver delay by reducing the number of vehicle signal phases. The success of converting to the split intersection is analyzed by using microsimulation. A phasing traffic flow is developed as a proof of concept. A Vehicle-to-Everything (V2X) traffic scenario is stablished and the experimental results confirm the cooperative Visible Light Communication (VLC) architecture showing that communication between connected bicycles and motor vehicles is optimized using a request/response concept. In this work, the communication between the infrastructures and the bicycles and motor vehicles, between vehicles and from the bicycles and motor vehicles to the infrastructures is performed through Visible Light Communication (VLC) using the street lamps and the traffic signaling to broadcast the information. 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) optical sensor, with light filtering properties, are used. The primary objective is to control the arrival of vehicles to an intersection and to schedule them to cross it at times that minimizes delays. A Vehicle-to-Everything (V2X) traffic scenario is stablished and bidirectional communication between the infrastructure and the vehicles is tested, using the VLC request/response concept.