Optical EngineeringIllumination design of a white-light-emitting diode wireless transmission system
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Conventional wireless communications make use of radio frequency. However, congestion and regulation of the spectrum have led to a search for alternatives. White-light-emitting diodes (WLEDs) can be modulated similarly to communications-wavelength infrared-light-emitting diodes. For WLEDs to be used for both wireless communication or an illumination, they have to be arranged in a manner that achieves a minimum signal power. To achieve this, an optimization routine has been created that optimizes the angular arrangement of the WLEDs to meet a predetermined illumination level. The irradiation profiles of the WLEDs are modeled for arbitrary tilt angles using a combination of theoretical expressions and experimental data. Lamps were created with 120 WLEDs each and implemented using the optimized angles. To demonstrate the use of the WLED wireless system in the transmission of audio signals, driving circuits were designed and implemented. The complete system was tested, and it is shown that the illumination levels meet the minimum required level. Characterization of the received signals shows a maximum ratio of bit energy to noise power density of 11.8 dB, corresponding to a bit error rate of 10-4.