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- Optical processor based on a-SiC technology for spectral data error controlPublication . Vieira, Manuel; Vieira, Manuela; Vaz da Silva, V; Louro, PaulaThe SiC optical processor for error detection and correction is realized by using double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Data shows that the background act as selector that pick one or more states by splitting portions of the input multi optical signals across the front and back photodiodes. Boolean operations such as exclusive OR (EXOR) and three bit addition are demonstrated optically with a combination of such switching devices, showing that when one or all of the inputs are present the output will be amplified, the system will behave as an XOR gate representing the SUM. When two or three inputs are on, the system acts as AND gate indicating the present of the CARRY bit. Additional parity logic operations are performed by use of the four incoming pulsed communication channels that are transmitted and checked for errors together. As a simple example of this approach, we describe an all optical processor for error detection and correction and then, provide an experimental demonstration of this fault tolerant reversible system, in emerging nanotechnology.
- Light memory function in a double pin SiC devicePublication . Vaz da Silva, V; Vieira, Manuela; Vieira, Manuel; Louro, Paula; Barata, ManuelA double pi'npin heterostructure based on amorphous SiC has a non linear spectral gain which is a function of the signal wavelength that impinges on its front or back surface. An impulse of a configurable length and amplitude is applied to a 390 nm LED which illuminates one of the sensor surfaces, followed by a time period without any illumination after which an input signal with a different wavelength is impinged upon the front surface. Results show that the intensity and duration of the impulse illumination of the surfaces influences the sensor's response with different output for the same input signal. This paper studies this effect and proposes an application as a short term light memory. (C) 2015 Elsevier B.V. All rights reserved.
- Optical signal processing for data error detection and correction using a-SiCH technologyPublication . Vieira, Manuel; Vieira, Manuela; Silva, V.; Louro, Paula; Costa, JoãoIn this paper, we explore the nonlinear properties of SiC multilayer devices under UV irradiation to design an optical processor for error detection and correction, that enables reliable delivery of spectral data of four-wave mixing over unreliable communication channels. The SiC optical processor for error detection and correction is realized by using a SiC pin/pin photodetector with UV biased optical gating elements. The relationship between the optical inputs and the corresponding digital output levels is established. Data shows that the optical bias act as a selector that picks one or more states by splitting portions of the input multi optical signals across the front and back photodiodes. Boolean operations are demonstrated optically, additional parity logic operations are performed and checked for errors together. As an example we describe an all-optical processor for error detection and correction and then, provide an experimental demonstration of this fault tolerant reversible system. An intuitive representation with a 4 bit original string coloured message and the transmitted 7 bit string, the parity matrix, the encoding and decoding processes and the design of SiC syndrome generators are presented.
- Direct Color Sensor, Optical Amplifier and Demux Device Integrated on a Single Monolithic SiC PhotodetectorPublication . Vieira, Manuela; Louro, Paula; Vieira, Manuel; Costa, João; Fernandes, MiguelA pi'n/pin a-SiC:H voltage and optical bias controlled device is presented and its behavior as image and color sensor, optical amplifier and demux device is discussed. The design and the light source properties are correlated with the sensor output characteristics. Different readout techniques are used. When a low power monochromatic scanner readout the generated carriers the transducer recognizes a color pattern projected on it acting as a direct color and image sensor. Scan speeds up to 10(4) lines per second are achieved without degradation in the resolution. If the photocurrent generated by different monochromatic pulsed channels is readout directly, the information is demultiplexed. Results show that it is possible to decode the information from three simultaneous color channels without bit errors at bit rates per channel higher than 4000 bps. Finally, when triggered by light of appropriated wavelength, it can amplify or suppress the generated photocurrent working as an optical amplifier (C) 2009 Published by Elsevier Ltd.
- Indoor positioning and intuitive advertising using visible light communicationPublication . Vieira, Manuela; Vieira, Manuel; Louro, Paula; Fantoni, Alessandro; Vieira, PedroThis paper researches the applicability of an intuitive advertising system for large indoor environments using Visible Light Communication (VLC). This VLC based positioning system includes the use of the visible light signal to light the space and to transmit the information for travelers’ positioning and of advertising campaigns in the surroundings. White RGB-LEDs, whose original function is providing illumination, are used as transmitters due to the ability of each individual chip to switch quickly enough to transfer data. This functionality is used for communication where the multiplexed data can be encoded in the emitting light. The light signals emitted by the LEDs positioned in the area of the advertising campaign are interpreted directly by the customers’ receivers. A SiC optical sensor with light filtering and demultiplexing properties receives the modulated signals containing the ID and the geographical position of the LED and other information, demultiplexes and decodes the data and locates the mobile device in the environment. Different layouts are analysed: square and hexagonal meshes are tested, and a 2D localization design, demonstrated by a prototype implementation, is presented. The key differences between both topologies are discussed. For both, the transmitted information, indoor position and motion direction of the customer are determined. The results showed that the LED-aided VLC navigation system enables to determine the position of a mobile target inside the network, to infer the travel direction as a function of time and to interact with information received.
- An optical processor for data error detection and correction using a (9,5) binary code generator and the syndrome decoding processPublication . Vieira, Manuel; Vieira, Manuela; Louro, Paula; Silva, Vítor; Costa, JBased on a-SiC:H technology, we present an optical processor for data error detection and correction using a suitable (9,5) Hamming binary code generator and the syndrome decoding process. The optical processor consists of an a-SiC:H double p-i-n photodetector with two ultraviolet light biased gates. The relationship between the optical inputs (transmitted data) and the corresponding output levels (the received data) is established and decoded. Results show that under irradiation the device acts as an active filter. Under front irradiation the magnitude of the short wavelength is quenched and in the long wavelength range is enlarged, while the opposite happens under back lighting. Parity bits are generated and stored simultaneously with the data word. Parity logic operations are performed and checked for errors together. An all-optical processor for error detection and correction is presented to provide an experimental demonstration of this fault tolerant reversible system. Two original coloured string messages, having 4- and 5- bits, respectively, are analyzed and the transmitted 7- or 9- bit string, the parity matrix, the encoding and decoding processes, are explained. The design of SiC syndrome generators for error correction is tested.
- Wayfinding services in crowded buildings through visible lightPublication . Vieira, Manuela; Vieira, Manuel; 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.
- 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.
- Geolocation and communication in unfamiliar indoor environments through visible lightPublication . Vieira, Manuela; Vieira, Manuel; Louro, Paula; Fantoni, Alessandro; Vieira, PedroTo support people’s wayfinding activities in unfamiliar indoor environments, a method able to generate ceiling landmark route instructions using Visible Light Communication (VLC) is proposed. The system is composed of several transmitters (ceiling luminaries) which send the map information and path messages required to wayfinding. Mobile optical receivers, using joint transmission, extracts theirs location to perform positioning and, concomitantly, the transmitted data from each transmitter. Bidirectional communication between the emitters and the receivers is available in strategic optical access point. Typical scenarios are simulated and include finding places and guiding users across different floors. 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, the modulated light signal, containing the ID and the 3D geographical position of the transmitter and wayfinding information, is received by SiC photodetectors 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. The coded light signals 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 and hexagonal topologies are tested, and a 3D localization design, demonstrated by a prototype is presented. Uplink transmission is implemented and the 3D best route to navigate through venue calculated. The results show 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 optimize the route towards a static or dynamic destination.