Abstract
Commercial-off-the-shelf (COTS) devices enabled visible light communication (VLC) for Internet of things (IoT) applications has attracted extensive attentions from both academic and industrial communities, thanks to the pervasive deployments of light emitting diode (LED) lighting infrastructure. However, due to the limitation of frequency response and non-linearity of the commercial illuminating LED light consisting of multiple LED chips, the achievable data rate is far less than that provided by the experimental VLC system with a single LED with specialized devices, e.g., lens. To this end, we propose a power-of-2 arrangement scheme for LED chips to generate spatial summing modulation with low control complexity, and demonstrate its availability in an orthogonal frequency division multiplexing (OFDM) VLC system purely built upon COTS devices. It significantly differs from a conventional OFDM VLC system relying on digital-to-analog converter (DAC) and analog signal chain, which is complex and confined by LED's non-linearity, thanks to we design a novel digital-to-light converter (DLC) which can output 256 light intensities linearly and be directly controlled by the discrete digital signals generated by the OFDM modulator. An experimental demonstration with employing the QAM-OFDM modulation scheme successfully confirms the effectiveness of the proposed spatial summing VLC system, which can achieve low BERs of below the forward error correct (FEC) threshold of 3.8×10-3 for both QAM8 and QAM16 running transmission frequency of 300 kHz under a communication distance of 0.8 m. It demonstrates the promising potential for delivering a data rate at hundred kbps level with this novel spatial summing based OFDM VLC system, which is sufficient for many IoT applications.
Highlights
With the booming grows of Internet of Things (IoT) devices, the generated huge sensed data is far beyond the capacity of existing radio-frequency (RF) communication techniques
We propose a power-of-2 arrangement scheme for light emitting diode (LED) chips to generate spatial summing modulation with low control complexity, and demonstrate its availability in an orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) system purely built upon COTS devices
It significantly differs from a conventional OFDM VLC system relying on digital-to-analog converter (DAC) and analog signal chain, which is complex and confined by LED’s non-linearity, thanks to we design a novel digital-to-light converter (DLC) which can output 256 light intensities linearly and be directly controlled by the discrete digital signals generated by the OFDM modulator
Summary
With the booming grows of Internet of Things (IoT) devices, the generated huge sensed data is far beyond the capacity of existing radio-frequency (RF) communication techniques. In order to mitigate the LED non-linearity and improve the spectral efficiency, spatial summing (or grouped) modulation has been proposed in [11,12,13] for single carrier VLC systems recently. Spatial summing modulation can directly generate discrete light intensities which represent signal symbols by controlling the number of alight LED chips in an LED array with only "on"/"off" logic. This concise control logic alleviates the linearity constraints of the illuminating LED chips. Using the spatial summing modulation scheme to generate OFDM signals without the bother of LED non-linearity is exactly feasible and cost-effective.
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