Constellation Design for Multi-color Visible Light Communications

In this paper, we propose a novel high dimensional constellation design scheme for visible light communication (VLC) systems employing red/green/blue light emitting diodes (RGB LEDs). It is in fact a generalized color shift keying (CSK) scheme which does not suffer efficiency loss due to a constrained sum intensity for all constellation symbols. Crucial lighting requirements are included as optimization constraints. To control non-linear distortion, the optical peak-to-average-power ratio (PAPR) of LEDs is individually constrained. Fixing the average optical power, our scheme is able to achieve much lower bit-error rate (BER) than conventional schems especially when illumination color is more "unbalanced". When cross-talks exist among the multiple optical channels, we apply a singular value decomposition (SVD)-based pre-equalizer and redesign the constellations, and such scheme is shown to outperform post-equalized schemes based on zero-forcing or linear minimum-mean-squared-error (LMMSE) principles. To further reduce system BER, a binary switching algorithm (BSA) is employed the first time for labeling high dimensional constellation. We thus obtains the optimal bits-to-symbols mapping.

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