Indoor visible light communication (VLC) has seen major growth in the last decade, reaching data rates in the Gbps range over 10 m distance. Its main limiting factors however are the low speed of the optoelectronic devices as well as the ambient noise reducing the system performance and reliability. The interference due to the artificial white light sources used for illumination in an indoor environment is one of the major noise sources challenging the performance of the VLC indoor channel. Since these noise sources operate at different frequencies, filtering their DC effect out does not eliminate their effect. This paper practically measures the noise power of the contemporary artificial light sources in an indoor visible light link to characterize their effect. The measurements show that thermal light sources cause a high noise power in a limited bandwidth of a few hundreds of Hz, while gas discharge lamps and dimmed semiconductor light sources have a much wider significant noise spectrum. An interference model to determine the overall noise power due to said sources is then deduced.
This paper proposes a low-complexity and energy-efficient light emitting diode (LED)-to-LED communication system for Internet of Things (IoT) devices with data rates up to 200 kbps over an error-free transmission distance up to 7 cm. The system is based on off-the-shelf red-green-blue (RGB) LEDs, of which the red sub-LED is employed as photodetector in photovoltaic mode while the green sub-LED is the transmitter. The LED photodetector is characterized in the terms of its noise characteristics and its response to the light intensity. The system performance is then analysed in terms of bandwidth, bit error rate (BER) and the signal to noise ratio (SNR). A matched filter is proposed, which optimises the performance and increases the error-free distance.
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