Browsing by Author "Wilfert, Otakar"
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- Consumer LED lamp with ODAC technology for high-speed visible light communicationsPublication . Figueiredo, Mónica; Ribeiro, Carlos; Dobesch, Ales; Alves, Luís N.; Wilfert, OtakarOptical digital-to-analog converters (ODACs) were recently proposed to mitigate the non-linear characteristic of light emitting diodes (LEDs) and to simplify the transceiver in optical wireless communication systems. This paper describes the implementation and performance of an ODAC lamp built with commercial phosphor coated LEDs. It is shown to have sufficient performance to cope with data-rates compatible with those recommended for Ultra HD quality internet download speed (25Mbps), despite the very low bandwidth of these LEDs. Also, the structure of a low-cost and high-speed OFDM-based Visible Light Communication transceiver, based on commercial LEDs and off-the-shelf components, is presented. This solution does not require D/A conversion or complex LED driving circuitry in the transmitter, which are usually seen as limiting factors to the deployment of high-speed VLC systems in the consumer LED lighting market.
- ODAC-based traffic lights for intelligent transport systemsPublication . Dobesch, Ales; Alves, Luis Nero; Wilfert, Otakar; Ribeiro, Carlos GasparThe optical digital to analog converter (ODAC) concept is introduced to be used in an intelligent transportation system (ITS). The paper explores the performance of ODAC adapted into a traffic light head in order to enable transferring information from the infrastructure to the vehicle (I2V). The performance of such a scenario is shown by reconstructing error as a function of emitter placement, LED’s half power angle (HPA) and receiver’s field of view (FOV). The obtained results reveal that ODAC performance strictly depends on geometrical deployment. Moreover, increasing signal frequency additionally introduces noticeable signal distortion.
- Optical digital to analog conversion performance analysis for indoor set-up conditionsPublication . Dobesch, Aleš; Alves, Luis Nero; Wilfert, Otakar; Ribeiro, Carlos GasparIn visible light communication (VLC) the optical digital to analog conversion (ODAC) approach was proposed as a suitable driving technique able to overcome light-emitting diode’s (LED) non-linear characteristic. This concept is analogous to an electrical digital-to-analog converter (EDAC). In other words, digital bits are binary weighted to represent an analog signal. The method supports elementary on–off based modulations able to exploit the essence of LED’s non-linear characteristic allowing simultaneous lighting and communication. In the ODAC concept the reconstruction error does not simply rely upon the converter bit depth as in case of EDAC. It rather depends on communication system set-up and geometrical relation between emitter and receiver as well. The paper describes simulation results presenting the ODAC’s error performance taking into account: the optical channel, the LED’s half power angle (HPA) and the receiver field of view (FOV). The set-up under consideration examines indoor conditions for a square room with 4 m length and 3 m height, operating with one dominant wavelength (blue) and having walls with a reflection coefficient of 0.8. The achieved results reveal that reconstruction error increases for higher data rates as a result of interference due to multipath propagation.