Digital Color Shift Keying With Multicolor LED Array

Color shift keying (CSK) is a visible light communication (VLC) intensity modulation scheme, which is outlined in IEEE 802.15.7, that transmits data imperceptibly through the variation of the color emitted by red, green, and blue light-emitting diodes (RGB LEDs). In this paper, digital CSK (DCSK) is presented, which represents CSK symbols by digitally controlled multiple multicolor LEDs to avoid the effect of LED nonlinearity. By using this scheme, the DCSK system using nine RGB LEDs can transmit IEEE 802.15.7 CSK constellations with an error-vector-magnitude (EVM) performance on an x-y chromaticity of 3%. The bit-error-rate (BER) evaluation of both the conventional and the proposed DCSK system shows that the DCSK system achieves similar BER to that of CSK with a linear variable current driver including predistortion, with taking into account optical wireless channels including the LED response, undesired color shift, and channel crosstalk by the practice characteristics of RGB LEDs, RGB bandpass filters, and photodiodes.